Message-ID: <20160221130614.GA4511@GLSMBP.INI.CMU.EDU>
Date:	Sun, 21 Feb 2016 08:06:17 -0500
From:	"Gabriel L. Somlo" <somlo@....edu>
To:	"Michael S. Tsirkin" <mst@...hat.com>
Cc:	gregkh@...uxfoundation.org, robh+dt@...nel.org, pawel.moll@....com,
	mark.rutland@....com, ijc+devicetree@...lion.org.uk,
	galak@...eaurora.org, arnd@...db.de, lersek@...hat.com,
	ralf@...ux-mips.org, rmk+kernel@....linux.org.uk, eric@...olt.net,
	hanjun.guo@...aro.org, zajec5@...il.com, sudeep.holla@....com,
	agross@...eaurora.org, linux-api@...r.kernel.org,
	linux-kernel@...r.kernel.org, devicetree@...r.kernel.org,
	qemu-devel@...gnu.org, imammedo@...hat.com,
	peter.maydell@...aro.org, leif.lindholm@...aro.org,
	ard.biesheuvel@...aro.org, pbonzini@...hat.com, kraxel@...hat.com,
	ehabkost@...hat.com, luto@...capital.net, stefanha@...il.com,
	revol@...e.fr, matt@...eblueprint.co.uk, rth@...ddle.net
Subject: Re: [PATCH v8 1/4] firmware: introduce sysfs driver for QEMU's
 fw_cfg device

On Sun, Feb 21, 2016 at 10:30:26AM +0200, Michael S. Tsirkin wrote:
> On Thu, Jan 28, 2016 at 09:23:11AM -0500, Gabriel L. Somlo wrote:
> > From: Gabriel Somlo <somlo@....edu>
> > 
> > Make fw_cfg entries of type "file" available via sysfs. Entries
> > are listed under /sys/firmware/qemu_fw_cfg/by_key, in folders
> > named after each entry's selector key. Filename, selector value,
> > and size read-only attributes are included for each entry. Also,
> > a "raw" attribute allows retrieval of the full binary content of
> > each entry.
> > 
> > The fw_cfg device can be instantiated automatically from ACPI or
> > the Device Tree, or manually by using a kernel module (or command
> > line) parameter, with a syntax outlined in the documentation file.
> > 
> > Signed-off-by: Gabriel Somlo <somlo@....edu>
> > ---
> >  .../ABI/testing/sysfs-firmware-qemu_fw_cfg         |  58 ++
> >  drivers/firmware/Kconfig                           |  19 +
> >  drivers/firmware/Makefile                          |   1 +
> >  drivers/firmware/qemu_fw_cfg.c                     | 648 +++++++++++++++++++++
> >  4 files changed, 726 insertions(+)
> >  create mode 100644 Documentation/ABI/testing/sysfs-firmware-qemu_fw_cfg
> >  create mode 100644 drivers/firmware/qemu_fw_cfg.c
> > 
> > diff --git a/Documentation/ABI/testing/sysfs-firmware-qemu_fw_cfg b/Documentation/ABI/testing/sysfs-firmware-qemu_fw_cfg
> > new file mode 100644
> > index 0000000..e9e58d4
> > --- /dev/null
> > +++ b/Documentation/ABI/testing/sysfs-firmware-qemu_fw_cfg
> > @@ -0,0 +1,58 @@
> > +What:		/sys/firmware/qemu_fw_cfg/
> > +Date:		August 2015
> > +Contact:	Gabriel Somlo <somlo@....edu>
> > +Description:
> > +		Several different architectures supported by QEMU (x86, arm,
> > +		sun4*, ppc/mac) are provisioned with a firmware configuration
> > +		(fw_cfg) device, originally intended as a way for the host to
> > +		provide configuration data to the guest firmware. Starting
> > +		with QEMU v2.4, arbitrary fw_cfg file entries may be specified
> > +		by the user on the command line, which makes fw_cfg additionally
> > +		useful as an out-of-band, asynchronous mechanism for providing
> > +		configuration data to the guest userspace.
> > +
> > +		The authoritative guest-side hardware interface documentation
> > +		to the fw_cfg device can be found in "docs/specs/fw_cfg.txt"
> > +		in the QEMU source tree.
> > +
> > +		=== SysFS fw_cfg Interface ===
> > +
> > +		The fw_cfg sysfs interface described in this document is only
> > +		intended to display discoverable blobs (i.e., those registered
> > +		with the file directory), as there is no way to determine the
> > +		presence or size of "legacy" blobs (with selector keys between
> > +		0x0002 and 0x0018) programmatically.
> > +
> > +		All fw_cfg information is shown under:
> > +
> > +			/sys/firmware/qemu_fw_cfg/
> > +
> > +		The only legacy blob displayed is the fw_cfg device revision:
> > +
> > +			/sys/firmware/qemu_fw_cfg/rev
> > +
> > +		--- Discoverable fw_cfg blobs by selector key ---
> > +
> > +		All discoverable blobs listed in the fw_cfg file directory are
> > +		displayed as entries named after their unique selector key
> > +		value, e.g.:
> > +
> > +			/sys/firmware/qemu_fw_cfg/by_key/32
> > +			/sys/firmware/qemu_fw_cfg/by_key/33
> > +			/sys/firmware/qemu_fw_cfg/by_key/34
> > +			...
> > +
> > +		Each such fw_cfg sysfs entry has the following values exported
> > +		as attributes:
> > +
> > +		name  	: The 56-byte nul-terminated ASCII string used as the
> > +			  blob's 'file name' in the fw_cfg directory.
> > +		size  	: The length of the blob, as given in the fw_cfg
> > +			  directory.
> > +		key	: The value of the blob's selector key as given in the
> > +			  fw_cfg directory. This value is the same as used in
> > +			  the parent directory name.
> > +		raw	: The raw bytes of the blob, obtained by selecting the
> > +			  entry via the control register, and reading a number
> > +			  of bytes equal to the blob size from the data
> > +			  register.
> > diff --git a/drivers/firmware/Kconfig b/drivers/firmware/Kconfig
> > index 49a3a11..5130f74 100644
> > --- a/drivers/firmware/Kconfig
> > +++ b/drivers/firmware/Kconfig
> > @@ -161,6 +161,25 @@ config RASPBERRYPI_FIRMWARE
> >  	  This option enables support for communicating with the firmware on the
> >  	  Raspberry Pi.
> >  
> > +config FW_CFG_SYSFS
> > +	tristate "QEMU fw_cfg device support in sysfs"
> > +	depends on SYSFS && (ARM || ARM64 || PPC_PMAC || SPARC || X86)
> > +	default n
> > +	help
> > +	  Say Y or M here to enable the exporting of the QEMU firmware
> > +	  configuration (fw_cfg) file entries via sysfs. Entries are
> > +	  found under /sys/firmware/fw_cfg when this option is enabled
> > +	  and loaded.
> > +
> > +config FW_CFG_SYSFS_CMDLINE
> > +	bool "QEMU fw_cfg device parameter parsing"
> > +	depends on FW_CFG_SYSFS
> > +	help
> > +	  Allow the qemu_fw_cfg device to be initialized via the kernel
> > +	  command line or using a module parameter.
> > +	  WARNING: Using incorrect parameters (base address in particular)
> > +	  may crash your system.
> > +
> >  config QCOM_SCM
> >  	bool
> >  	depends on ARM || ARM64
> > diff --git a/drivers/firmware/Makefile b/drivers/firmware/Makefile
> > index 48dd417..474bada 100644
> > --- a/drivers/firmware/Makefile
> > +++ b/drivers/firmware/Makefile
> > @@ -14,6 +14,7 @@ obj-$(CONFIG_ISCSI_IBFT_FIND)	+= iscsi_ibft_find.o
> >  obj-$(CONFIG_ISCSI_IBFT)	+= iscsi_ibft.o
> >  obj-$(CONFIG_FIRMWARE_MEMMAP)	+= memmap.o
> >  obj-$(CONFIG_RASPBERRYPI_FIRMWARE) += raspberrypi.o
> > +obj-$(CONFIG_FW_CFG_SYSFS)	+= qemu_fw_cfg.o
> >  obj-$(CONFIG_QCOM_SCM)		+= qcom_scm.o
> >  obj-$(CONFIG_QCOM_SCM_64)	+= qcom_scm-64.o
> >  obj-$(CONFIG_QCOM_SCM_32)	+= qcom_scm-32.o
> > diff --git a/drivers/firmware/qemu_fw_cfg.c b/drivers/firmware/qemu_fw_cfg.c
> > new file mode 100644
> > index 0000000..83e8a5c
> > --- /dev/null
> > +++ b/drivers/firmware/qemu_fw_cfg.c
> > @@ -0,0 +1,648 @@
> > +/*
> > + * drivers/firmware/qemu_fw_cfg.c
> > + *
> > + * Copyright 2015 Carnegie Mellon University
> > + *
> > + * Expose entries from QEMU's firmware configuration (fw_cfg) device in
> > + * sysfs (read-only, under "/sys/firmware/qemu_fw_cfg/...").
> > + *
> > + * The fw_cfg device may be instantiated via either an ACPI node (on x86
> > + * and select subsets of aarch64), a Device Tree node (on arm), or using
> > + * a kernel module (or command line) parameter with the following syntax:
> > + *
> > + *      [fw_cfg.]ioport=<size>@<base>[:<ctrl_off>:<data_off>]
> > + * or
> > + *      [fw_cfg.]mmio=<size>@<base>[:<ctrl_off>:<data_off>]
> > + *
> > + * where:
> > + *      <size>     := size of ioport or mmio range
> > + *      <base>     := physical base address of ioport or mmio range
> > + *      <ctrl_off> := (optional) offset of control register
> > + *      <data_off> := (optional) offset of data register
> > + *
> > + * e.g.:
> > + *      fw_cfg.ioport=2@...10:0:1		(the default on x86)
> > + * or
> > + *      fw_cfg.mmio=0xA@...020000:8:0		(the default on arm)
> > + */
> > +
> > +#include <linux/module.h>
> > +#include <linux/platform_device.h>
> > +#include <linux/acpi.h>
> > +#include <linux/slab.h>
> > +#include <linux/io.h>
> > +#include <linux/ioport.h>
> > +
> > +MODULE_AUTHOR("Gabriel L. Somlo <somlo@....edu>");
> > +MODULE_DESCRIPTION("QEMU fw_cfg sysfs support");
> > +MODULE_LICENSE("GPL");
> > +
> > +/* selector key values for "well-known" fw_cfg entries */
> > +#define FW_CFG_SIGNATURE  0x00
> > +#define FW_CFG_ID         0x01
> > +#define FW_CFG_FILE_DIR   0x19
> > +
> > +/* size in bytes of fw_cfg signature */
> > +#define FW_CFG_SIG_SIZE 4
> > +
> > +/* fw_cfg "file name" is up to 56 characters (including terminating nul) */
> > +#define FW_CFG_MAX_FILE_PATH 56
> > +
> > +/* fw_cfg file directory entry type */
> > +struct fw_cfg_file {
> > +	u32 size;
> > +	u16 select;
> > +	u16 reserved;
> > +	char name[FW_CFG_MAX_FILE_PATH];
> > +};
> > +
> > +/* fw_cfg device i/o register addresses */
> > +static bool fw_cfg_is_mmio;
> > +static phys_addr_t fw_cfg_p_base;
> > +static resource_size_t fw_cfg_p_size;
> > +static void __iomem *fw_cfg_dev_base;
> > +static void __iomem *fw_cfg_reg_ctrl;
> > +static void __iomem *fw_cfg_reg_data;
> > +
> > +/* atomic access to fw_cfg device (potentially slow i/o, so using mutex) */
> > +static DEFINE_MUTEX(fw_cfg_dev_lock);
> > +
> > +/* pick appropriate endianness for selector key */
> > +static inline u16 fw_cfg_sel_endianness(u16 key)
> > +{
> > +	return fw_cfg_is_mmio ? cpu_to_be16(key) : cpu_to_le16(key);
> > +}
> > +
> > +/* read chunk of given fw_cfg blob (caller responsible for sanity-check) */
> > +static inline void fw_cfg_read_blob(u16 key,
> > +				    void *buf, loff_t pos, size_t count)
> > +{
> > +	mutex_lock(&fw_cfg_dev_lock);
> > +	iowrite16(fw_cfg_sel_endianness(key), fw_cfg_reg_ctrl);
> > +	while (pos-- > 0)
> > +		ioread8(fw_cfg_reg_data);
> > +	ioread8_rep(fw_cfg_reg_data, buf, count);
> > +	mutex_unlock(&fw_cfg_dev_lock);
> > +}
> 
> This locking is not enough I think: ACPI might be
> accessing FW CFG meanwhile, and assuming it's
> the only owner.
> 
> I think that on systems that support ACPI,
> it would be better to use an ACPI interface
> to read blobs, instead of poking on _CRS and banging on registers directly.
> 
> This will also make it easier to extend the interface,
> and support DMA.
> 
> 
> 
> > +
> > +/* clean up fw_cfg device i/o */
> > +static void fw_cfg_io_cleanup(void)
> > +{
> > +	if (fw_cfg_is_mmio) {
> > +		iounmap(fw_cfg_dev_base);
> > +		release_mem_region(fw_cfg_p_base, fw_cfg_p_size);
> > +	} else {
> > +		ioport_unmap(fw_cfg_dev_base);
> > +		release_region(fw_cfg_p_base, fw_cfg_p_size);
> > +	}
> > +}
> > +
> > +/* arch-specific ctrl & data register offsets are not available in ACPI, DT */
> 
> So for all arches which support ACPI, I think this driver
> should just rely on ACPI.

There was a discussion about that a few versions ago, and IIRC the
conclusion was not to expect the firmware to contend for fw_cfg access
after the guest kernel boots:

https://lkml.org/lkml/2015/10/5/283

(I even had a prototype version doing what you suggested, but per the above
reference decided to drop it -- which IMHO is for the better, since otherwise
I'd have had to ifdef between ACPI and non-ACPI versions of the driver --
see https://lkml.org/lkml/2015/11/4/534 )


> 
> > +#if !(defined(FW_CFG_CTRL_OFF) && defined(FW_CTRL_DATA_OFF))
> > +# if (defined(CONFIG_ARM) || defined(CONFIG_ARM64))
> > +#  define FW_CFG_CTRL_OFF 0x08
> > +#  define FW_CFG_DATA_OFF 0x00
> > +# elif (defined(CONFIG_PPC_PMAC) || defined(CONFIG_SPARC32)) /* ppc/mac,sun4m */
> > +#  define FW_CFG_CTRL_OFF 0x00
> > +#  define FW_CFG_DATA_OFF 0x02
> > +# elif (defined(CONFIG_X86) || defined(CONFIG_SPARC64)) /* x86, sun4u */
> > +#  define FW_CFG_CTRL_OFF 0x00
> > +#  define FW_CFG_DATA_OFF 0x01
> > +# else
> > +#  warning "QEMU FW_CFG may not be available on this architecture!"
> > +#  define FW_CFG_CTRL_OFF 0x00
> > +#  define FW_CFG_DATA_OFF 0x01
> 
> Better not try hacks like this, they are hard
> to support down the road. Please only list what is tested and
> actually exposed by QEMU.

I was looking for a standard way to advertise register offsets within
the ioport or mmio region assigned to fw_cfg, but right now the answer
is "there isn't one", and "register offsets are an arch specific
detail". As such, the only reasonable way I saw was to copy the same
values used in the QEMU source.

See also:
https://lists.gnu.org/archive/html/qemu-devel/2015-11/msg05037.html
 
Thanks much,
--Gabriel

> 
> > +# endif
> > +#endif
> > +
> > +/* initialize fw_cfg device i/o from platform data */
> > +static int fw_cfg_do_platform_probe(struct platform_device *pdev)
> > +{
> > +	char sig[FW_CFG_SIG_SIZE];
> > +	struct resource *range, *ctrl, *data;
> > +
> > +	/* acquire i/o range details */
> > +	fw_cfg_is_mmio = false;
> > +	range = platform_get_resource(pdev, IORESOURCE_IO, 0);
> > +	if (!range) {
> > +		fw_cfg_is_mmio = true;
> > +		range = platform_get_resource(pdev, IORESOURCE_MEM, 0);
> > +		if (!range)
> > +			return -EINVAL;
> > +	}
> > +	fw_cfg_p_base = range->start;
> > +	fw_cfg_p_size = resource_size(range);
> > +
> > +	if (fw_cfg_is_mmio) {
> > +		if (!request_mem_region(fw_cfg_p_base,
> > +					fw_cfg_p_size, "fw_cfg_mem"))
> > +			return -EBUSY;
> > +		fw_cfg_dev_base = ioremap(fw_cfg_p_base, fw_cfg_p_size);
> > +		if (!fw_cfg_dev_base) {
> > +			release_mem_region(fw_cfg_p_base, fw_cfg_p_size);
> > +			return -EFAULT;
> > +		}
> > +	} else {
> > +		if (!request_region(fw_cfg_p_base,
> > +				    fw_cfg_p_size, "fw_cfg_io"))
> > +			return -EBUSY;
> > +		fw_cfg_dev_base = ioport_map(fw_cfg_p_base, fw_cfg_p_size);
> > +		if (!fw_cfg_dev_base) {
> > +			release_region(fw_cfg_p_base, fw_cfg_p_size);
> > +			return -EFAULT;
> > +		}
> > +	}
> > +
> > +	/* were custom register offsets provided (e.g. on the command line)? */
> > +	ctrl = platform_get_resource_byname(pdev, IORESOURCE_REG, "ctrl");
> > +	data = platform_get_resource_byname(pdev, IORESOURCE_REG, "data");
> > +	if (ctrl && data) {
> > +		fw_cfg_reg_ctrl = fw_cfg_dev_base + ctrl->start;
> > +		fw_cfg_reg_data = fw_cfg_dev_base + data->start;
> > +	} else {
> > +		/* use architecture-specific offsets */
> > +		fw_cfg_reg_ctrl = fw_cfg_dev_base + FW_CFG_CTRL_OFF;
> > +		fw_cfg_reg_data = fw_cfg_dev_base + FW_CFG_DATA_OFF;
> > +	}
> > +
> > +	/* verify fw_cfg device signature */
> > +	fw_cfg_read_blob(FW_CFG_SIGNATURE, sig, 0, FW_CFG_SIG_SIZE);
> > +	if (memcmp(sig, "QEMU", FW_CFG_SIG_SIZE) != 0) {
> > +		fw_cfg_io_cleanup();
> > +		return -ENODEV;
> > +	}
> > +
> > +	return 0;
> > +}
> > +
> > +/* fw_cfg revision attribute, in /sys/firmware/qemu_fw_cfg top-level dir. */
> > +static u32 fw_cfg_rev;
> > +
> > +static ssize_t fw_cfg_showrev(struct kobject *k, struct attribute *a, char *buf)
> > +{
> > +	return sprintf(buf, "%u\n", fw_cfg_rev);
> > +}
> > +
> > +static const struct {
> > +	struct attribute attr;
> > +	ssize_t (*show)(struct kobject *k, struct attribute *a, char *buf);
> > +} fw_cfg_rev_attr = {
> > +	.attr = { .name = "rev", .mode = S_IRUSR },
> > +	.show = fw_cfg_showrev,
> > +};
> > +
> > +/* fw_cfg_sysfs_entry type */
> > +struct fw_cfg_sysfs_entry {
> > +	struct kobject kobj;
> > +	struct fw_cfg_file f;
> > +	struct list_head list;
> > +};
> > +
> > +/* get fw_cfg_sysfs_entry from kobject member */
> > +static inline struct fw_cfg_sysfs_entry *to_entry(struct kobject *kobj)
> > +{
> > +	return container_of(kobj, struct fw_cfg_sysfs_entry, kobj);
> > +}
> > +
> > +/* fw_cfg_sysfs_attribute type */
> > +struct fw_cfg_sysfs_attribute {
> > +	struct attribute attr;
> > +	ssize_t (*show)(struct fw_cfg_sysfs_entry *entry, char *buf);
> > +};
> > +
> > +/* get fw_cfg_sysfs_attribute from attribute member */
> > +static inline struct fw_cfg_sysfs_attribute *to_attr(struct attribute *attr)
> > +{
> > +	return container_of(attr, struct fw_cfg_sysfs_attribute, attr);
> > +}
> > +
> > +/* global cache of fw_cfg_sysfs_entry objects */
> > +static LIST_HEAD(fw_cfg_entry_cache);
> > +
> > +/* kobjects removed lazily by kernel, mutual exclusion needed */
> > +static DEFINE_SPINLOCK(fw_cfg_cache_lock);
> > +
> > +static inline void fw_cfg_sysfs_cache_enlist(struct fw_cfg_sysfs_entry *entry)
> > +{
> > +	spin_lock(&fw_cfg_cache_lock);
> > +	list_add_tail(&entry->list, &fw_cfg_entry_cache);
> > +	spin_unlock(&fw_cfg_cache_lock);
> > +}
> > +
> > +static inline void fw_cfg_sysfs_cache_delist(struct fw_cfg_sysfs_entry *entry)
> > +{
> > +	spin_lock(&fw_cfg_cache_lock);
> > +	list_del(&entry->list);
> > +	spin_unlock(&fw_cfg_cache_lock);
> > +}
> > +
> > +static void fw_cfg_sysfs_cache_cleanup(void)
> > +{
> > +	struct fw_cfg_sysfs_entry *entry, *next;
> > +
> > +	list_for_each_entry_safe(entry, next, &fw_cfg_entry_cache, list) {
> > +		/* will end up invoking fw_cfg_sysfs_cache_delist()
> > +		 * via each object's release() method (i.e. destructor)
> > +		 */
> > +		kobject_put(&entry->kobj);
> > +	}
> > +}
> > +
> > +/* default_attrs: per-entry attributes and show methods */
> > +
> > +#define FW_CFG_SYSFS_ATTR(_attr) \
> > +struct fw_cfg_sysfs_attribute fw_cfg_sysfs_attr_##_attr = { \
> > +	.attr = { .name = __stringify(_attr), .mode = S_IRUSR }, \
> > +	.show = fw_cfg_sysfs_show_##_attr, \
> > +}
> > +
> > +static ssize_t fw_cfg_sysfs_show_size(struct fw_cfg_sysfs_entry *e, char *buf)
> > +{
> > +	return sprintf(buf, "%u\n", e->f.size);
> > +}
> > +
> > +static ssize_t fw_cfg_sysfs_show_key(struct fw_cfg_sysfs_entry *e, char *buf)
> > +{
> > +	return sprintf(buf, "%u\n", e->f.select);
> > +}
> > +
> > +static ssize_t fw_cfg_sysfs_show_name(struct fw_cfg_sysfs_entry *e, char *buf)
> > +{
> > +	return sprintf(buf, "%s\n", e->f.name);
> > +}
> > +
> > +static FW_CFG_SYSFS_ATTR(size);
> > +static FW_CFG_SYSFS_ATTR(key);
> > +static FW_CFG_SYSFS_ATTR(name);
> > +
> > +static struct attribute *fw_cfg_sysfs_entry_attrs[] = {
> > +	&fw_cfg_sysfs_attr_size.attr,
> > +	&fw_cfg_sysfs_attr_key.attr,
> > +	&fw_cfg_sysfs_attr_name.attr,
> > +	NULL,
> > +};
> > +
> > +/* sysfs_ops: find fw_cfg_[entry, attribute] and call appropriate show method */
> > +static ssize_t fw_cfg_sysfs_attr_show(struct kobject *kobj, struct attribute *a,
> > +				      char *buf)
> > +{
> > +	struct fw_cfg_sysfs_entry *entry = to_entry(kobj);
> > +	struct fw_cfg_sysfs_attribute *attr = to_attr(a);
> > +
> > +	return attr->show(entry, buf);
> > +}
> > +
> > +static const struct sysfs_ops fw_cfg_sysfs_attr_ops = {
> > +	.show = fw_cfg_sysfs_attr_show,
> > +};
> > +
> > +/* release: destructor, to be called via kobject_put() */
> > +static void fw_cfg_sysfs_release_entry(struct kobject *kobj)
> > +{
> > +	struct fw_cfg_sysfs_entry *entry = to_entry(kobj);
> > +
> > +	fw_cfg_sysfs_cache_delist(entry);
> > +	kfree(entry);
> > +}
> > +
> > +/* kobj_type: ties together all properties required to register an entry */
> > +static struct kobj_type fw_cfg_sysfs_entry_ktype = {
> > +	.default_attrs = fw_cfg_sysfs_entry_attrs,
> > +	.sysfs_ops = &fw_cfg_sysfs_attr_ops,
> > +	.release = fw_cfg_sysfs_release_entry,
> > +};
> > +
> > +/* raw-read method and attribute */
> > +static ssize_t fw_cfg_sysfs_read_raw(struct file *filp, struct kobject *kobj,
> > +				     struct bin_attribute *bin_attr,
> > +				     char *buf, loff_t pos, size_t count)
> > +{
> > +	struct fw_cfg_sysfs_entry *entry = to_entry(kobj);
> > +
> > +	if (pos > entry->f.size)
> > +		return -EINVAL;
> > +
> > +	if (count > entry->f.size - pos)
> > +		count = entry->f.size - pos;
> > +
> > +	fw_cfg_read_blob(entry->f.select, buf, pos, count);
> > +	return count;
> > +}
> > +
> > +static struct bin_attribute fw_cfg_sysfs_attr_raw = {
> > +	.attr = { .name = "raw", .mode = S_IRUSR },
> > +	.read = fw_cfg_sysfs_read_raw,
> > +};
> > +
> > +/* kobjects representing top-level and by_key folders */
> > +static struct kobject *fw_cfg_top_ko;
> > +static struct kobject *fw_cfg_sel_ko;
> > +
> > +/* register an individual fw_cfg file */
> > +static int fw_cfg_register_file(const struct fw_cfg_file *f)
> > +{
> > +	int err;
> > +	struct fw_cfg_sysfs_entry *entry;
> > +
> > +	/* allocate new entry */
> > +	entry = kzalloc(sizeof(*entry), GFP_KERNEL);
> > +	if (!entry)
> > +		return -ENOMEM;
> > +
> > +	/* set file entry information */
> > +	memcpy(&entry->f, f, sizeof(struct fw_cfg_file));
> > +
> > +	/* register entry under "/sys/firmware/qemu_fw_cfg/by_key/" */
> > +	err = kobject_init_and_add(&entry->kobj, &fw_cfg_sysfs_entry_ktype,
> > +				   fw_cfg_sel_ko, "%d", entry->f.select);
> > +	if (err)
> > +		goto err_register;
> > +
> > +	/* add raw binary content access */
> > +	err = sysfs_create_bin_file(&entry->kobj, &fw_cfg_sysfs_attr_raw);
> > +	if (err)
> > +		goto err_add_raw;
> > +
> > +	/* success, add entry to global cache */
> > +	fw_cfg_sysfs_cache_enlist(entry);
> > +	return 0;
> > +
> > +err_add_raw:
> > +	kobject_del(&entry->kobj);
> > +err_register:
> > +	kfree(entry);
> > +	return err;
> > +}
> > +
> > +/* iterate over all fw_cfg directory entries, registering each one */
> > +static int fw_cfg_register_dir_entries(void)
> > +{
> > +	int ret = 0;
> > +	u32 count, i;
> > +	struct fw_cfg_file *dir;
> > +	size_t dir_size;
> > +
> > +	fw_cfg_read_blob(FW_CFG_FILE_DIR, &count, 0, sizeof(count));
> > +	count = be32_to_cpu(count);
> > +	dir_size = count * sizeof(struct fw_cfg_file);
> > +
> > +	dir = kmalloc(dir_size, GFP_KERNEL);
> > +	if (!dir)
> > +		return -ENOMEM;
> > +
> > +	fw_cfg_read_blob(FW_CFG_FILE_DIR, dir, sizeof(count), dir_size);
> > +
> > +	for (i = 0; i < count; i++) {
> > +		dir[i].size = be32_to_cpu(dir[i].size);
> > +		dir[i].select = be16_to_cpu(dir[i].select);
> > +		ret = fw_cfg_register_file(&dir[i]);
> > +		if (ret)
> > +			break;
> > +	}
> > +
> > +	kfree(dir);
> > +	return ret;
> > +}
> > +
> > +/* unregister top-level or by_key folder */
> > +static inline void fw_cfg_kobj_cleanup(struct kobject *kobj)
> > +{
> > +	kobject_del(kobj);
> > +	kobject_put(kobj);
> > +}
> > +
> > +static int fw_cfg_sysfs_probe(struct platform_device *pdev)
> > +{
> > +	int err;
> > +
> > +	/* NOTE: If we supported multiple fw_cfg devices, we'd first create
> > +	 * a subdirectory named after e.g. pdev->id, then hang per-device
> > +	 * by_key subdirectories underneath it. However, only
> > +	 * one fw_cfg device exist system-wide, so if one was already found
> > +	 * earlier, we might as well stop here.
> > +	 */
> > +	if (fw_cfg_sel_ko)
> > +		return -EBUSY;
> > +
> > +	/* create by_key subdirectory of /sys/firmware/qemu_fw_cfg/ */
> > +	err = -ENOMEM;
> > +	fw_cfg_sel_ko = kobject_create_and_add("by_key", fw_cfg_top_ko);
> > +	if (!fw_cfg_sel_ko)
> > +		goto err_sel;
> > +
> > +	/* initialize fw_cfg device i/o from platform data */
> > +	err = fw_cfg_do_platform_probe(pdev);
> > +	if (err)
> > +		goto err_probe;
> > +
> > +	/* get revision number, add matching top-level attribute */
> > +	fw_cfg_read_blob(FW_CFG_ID, &fw_cfg_rev, 0, sizeof(fw_cfg_rev));
> > +	fw_cfg_rev = le32_to_cpu(fw_cfg_rev);
> > +	err = sysfs_create_file(fw_cfg_top_ko, &fw_cfg_rev_attr.attr);
> > +	if (err)
> > +		goto err_rev;
> > +
> > +	/* process fw_cfg file directory entry, registering each file */
> > +	err = fw_cfg_register_dir_entries();
> > +	if (err)
> > +		goto err_dir;
> > +
> > +	/* success */
> > +	pr_debug("fw_cfg: loaded.\n");
> > +	return 0;
> > +
> > +err_dir:
> > +	fw_cfg_sysfs_cache_cleanup();
> > +	sysfs_remove_file(fw_cfg_top_ko, &fw_cfg_rev_attr.attr);
> > +err_rev:
> > +	fw_cfg_io_cleanup();
> > +err_probe:
> > +	fw_cfg_kobj_cleanup(fw_cfg_sel_ko);
> > +err_sel:
> > +	return err;
> > +}
> > +
> > +static int fw_cfg_sysfs_remove(struct platform_device *pdev)
> > +{
> > +	pr_debug("fw_cfg: unloading.\n");
> > +	fw_cfg_sysfs_cache_cleanup();
> > +	fw_cfg_kobj_cleanup(fw_cfg_sel_ko);
> > +	fw_cfg_io_cleanup();
> > +	return 0;
> > +}
> > +
> > +static const struct of_device_id fw_cfg_sysfs_mmio_match[] = {
> > +	{ .compatible = "qemu,fw-cfg-mmio", },
> > +	{},
> > +};
> > +MODULE_DEVICE_TABLE(of, fw_cfg_sysfs_mmio_match);
> > +
> > +#ifdef CONFIG_ACPI
> > +static const struct acpi_device_id fw_cfg_sysfs_acpi_match[] = {
> > +	{ "QEMU0002", },
> > +	{},
> > +};
> > +MODULE_DEVICE_TABLE(acpi, fw_cfg_sysfs_acpi_match);
> > +#endif
> > +
> > +static struct platform_driver fw_cfg_sysfs_driver = {
> > +	.probe = fw_cfg_sysfs_probe,
> > +	.remove = fw_cfg_sysfs_remove,
> > +	.driver = {
> > +		.name = "fw_cfg",
> > +		.of_match_table = fw_cfg_sysfs_mmio_match,
> > +		.acpi_match_table = ACPI_PTR(fw_cfg_sysfs_acpi_match),
> > +	},
> > +};
> > +
> > +#ifdef CONFIG_FW_CFG_SYSFS_CMDLINE
> > +
> > +static struct platform_device *fw_cfg_cmdline_dev;
> > +
> > +/* this probably belongs in e.g. include/linux/types.h,
> > + * but right now we are the only ones doing it...
> > + */
> > +#ifdef CONFIG_PHYS_ADDR_T_64BIT
> > +#define __PHYS_ADDR_PREFIX "ll"
> > +#else
> > +#define __PHYS_ADDR_PREFIX ""
> > +#endif
> > +
> > +/* use special scanf/printf modifier for phys_addr_t, resource_size_t */
> > +#define PH_ADDR_SCAN_FMT "@%" __PHYS_ADDR_PREFIX "i%n" \
> > +			 ":%" __PHYS_ADDR_PREFIX "i" \
> > +			 ":%" __PHYS_ADDR_PREFIX "i%n"
> > +
> > +#define PH_ADDR_PR_1_FMT "0x%" __PHYS_ADDR_PREFIX "x@" \
> > +			 "0x%" __PHYS_ADDR_PREFIX "x"
> > +
> > +#define PH_ADDR_PR_3_FMT PH_ADDR_PR_1_FMT \
> > +			 ":%" __PHYS_ADDR_PREFIX "u" \
> > +			 ":%" __PHYS_ADDR_PREFIX "u"
> > +
> > +static int fw_cfg_cmdline_set(const char *arg, const struct kernel_param *kp)
> > +{
> > +	struct resource res[3] = {};
> > +	char *str;
> > +	phys_addr_t base;
> > +	resource_size_t size, ctrl_off, data_off;
> > +	int processed, consumed = 0;
> > +
> > +	/* only one fw_cfg device can exist system-wide, so if one
> > +	 * was processed on the command line already, we might as
> > +	 * well stop here.
> > +	 */
> > +	if (fw_cfg_cmdline_dev) {
> > +		/* avoid leaking previously registered device */
> > +		platform_device_unregister(fw_cfg_cmdline_dev);
> > +		return -EINVAL;
> > +	}
> > +
> > +	/* consume "<size>" portion of command line argument */
> > +	size = memparse(arg, &str);
> > +
> > +	/* get "@<base>[:<ctrl_off>:<data_off>]" chunks */
> > +	processed = sscanf(str, PH_ADDR_SCAN_FMT,
> > +			   &base, &consumed,
> > +			   &ctrl_off, &data_off, &consumed);
> > +
> > +	/* sscanf() must process precisely 1 or 3 chunks:
> > +	 * <base> is mandatory, optionally followed by <ctrl_off>
> > +	 * and <data_off>;
> > +	 * there must be no extra characters after the last chunk,
> > +	 * so str[consumed] must be '\0'.
> > +	 */
> > +	if (str[consumed] ||
> > +	    (processed != 1 && processed != 3))
> > +		return -EINVAL;
> > +
> > +	res[0].start = base;
> > +	res[0].end = base + size - 1;
> > +	res[0].flags = !strcmp(kp->name, "mmio") ? IORESOURCE_MEM :
> > +						   IORESOURCE_IO;
> > +
> > +	/* insert register offsets, if provided */
> > +	if (processed > 1) {
> > +		res[1].name = "ctrl";
> > +		res[1].start = ctrl_off;
> > +		res[1].flags = IORESOURCE_REG;
> > +		res[2].name = "data";
> > +		res[2].start = data_off;
> > +		res[2].flags = IORESOURCE_REG;
> > +	}
> > +
> > +	/* "processed" happens to nicely match the number of resources
> > +	 * we need to pass in to this platform device.
> > +	 */
> > +	fw_cfg_cmdline_dev = platform_device_register_simple("fw_cfg",
> > +					PLATFORM_DEVID_NONE, res, processed);
> > +	if (IS_ERR(fw_cfg_cmdline_dev))
> > +		return PTR_ERR(fw_cfg_cmdline_dev);
> > +
> > +	return 0;
> > +}
> > +
> > +static int fw_cfg_cmdline_get(char *buf, const struct kernel_param *kp)
> > +{
> > +	/* stay silent if device was not configured via the command
> > +	 * line, or if the parameter name (ioport/mmio) doesn't match
> > +	 * the device setting
> > +	 */
> > +	if (!fw_cfg_cmdline_dev ||
> > +	    (!strcmp(kp->name, "mmio") ^
> > +	     (fw_cfg_cmdline_dev->resource[0].flags == IORESOURCE_MEM)))
> > +		return 0;
> > +
> > +	switch (fw_cfg_cmdline_dev->num_resources) {
> > +	case 1:
> > +		return snprintf(buf, PAGE_SIZE, PH_ADDR_PR_1_FMT,
> > +				resource_size(&fw_cfg_cmdline_dev->resource[0]),
> > +				fw_cfg_cmdline_dev->resource[0].start);
> > +	case 3:
> > +		return snprintf(buf, PAGE_SIZE, PH_ADDR_PR_3_FMT,
> > +				resource_size(&fw_cfg_cmdline_dev->resource[0]),
> > +				fw_cfg_cmdline_dev->resource[0].start,
> > +				fw_cfg_cmdline_dev->resource[1].start,
> > +				fw_cfg_cmdline_dev->resource[2].start);
> > +	}
> > +
> > +	/* Should never get here */
> > +	WARN(1, "Unexpected number of resources: %d\n",
> > +		fw_cfg_cmdline_dev->num_resources);
> > +	return 0;
> > +}
> > +
> > +static const struct kernel_param_ops fw_cfg_cmdline_param_ops = {
> > +	.set = fw_cfg_cmdline_set,
> > +	.get = fw_cfg_cmdline_get,
> > +};
> > +
> > +device_param_cb(ioport, &fw_cfg_cmdline_param_ops, NULL, S_IRUSR);
> > +device_param_cb(mmio, &fw_cfg_cmdline_param_ops, NULL, S_IRUSR);
> > +
> > +#endif /* CONFIG_FW_CFG_SYSFS_CMDLINE */
> > +
> > +static int __init fw_cfg_sysfs_init(void)
> > +{
> > +	/* create /sys/firmware/qemu_fw_cfg/ top level directory */
> > +	fw_cfg_top_ko = kobject_create_and_add("qemu_fw_cfg", firmware_kobj);
> > +	if (!fw_cfg_top_ko)
> > +		return -ENOMEM;
> > +
> > +	return platform_driver_register(&fw_cfg_sysfs_driver);
> > +}
> > +
> > +static void __exit fw_cfg_sysfs_exit(void)
> > +{
> > +	platform_driver_unregister(&fw_cfg_sysfs_driver);
> > +
> > +#ifdef CONFIG_FW_CFG_SYSFS_CMDLINE
> > +	platform_device_unregister(fw_cfg_cmdline_dev);
> > +#endif
> > +
> > +	/* clean up /sys/firmware/qemu_fw_cfg/ */
> > +	fw_cfg_kobj_cleanup(fw_cfg_top_ko);
> > +}
> > +
> > +module_init(fw_cfg_sysfs_init);
> > +module_exit(fw_cfg_sysfs_exit);
> > -- 
> > 2.4.3

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