Date:   Mon, 6 Jun 2022 11:15:41 -0700
From:   Ben Widawsky <bwidawsk@...nel.org>
To:     ira.weiny@...el.com
Cc:     Dan Williams <dan.j.williams@...el.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Jonathan Cameron <Jonathan.Cameron@...wei.com>,
        Alison Schofield <alison.schofield@...el.com>,
        Vishal Verma <vishal.l.verma@...el.com>,
        Dave Jiang <dave.jiang@...el.com>,
        linux-kernel@...r.kernel.org, linux-cxl@...r.kernel.org,
        linux-pci@...r.kernel.org
Subject: Re: [PATCH V10 6/9] cxl/port: Read CDAT table

On 22-06-04 17:50:46, ira.weiny@...el.com wrote:
> From: Jonathan Cameron <Jonathan.Cameron@...wei.com>
> 
> The OS will need CDAT data from CXL devices to properly set up
> interleave sets.  Currently this is supported through a DOE mailbox
> which supports CDAT.
> 
> Cache the CDAT data for later parsing.  Provide a sysfs binary attribute
> to allow dumping of the CDAT.
> 
> Binary dumping is modeled on /sys/firmware/ACPI/tables/
> 
> The ability to dump this table will be very useful for emulation of real
> devices once they become available as QEMU CXL type 3 device emulation will
> be able to load this file in.
> 
> This does not support table updates at runtime. It will always provide
> whatever was there when first cached. Handling of table updates can be
> implemented later.
> 
> Finally create a complete list of DOE defines within cdat.h for code
> wishing to decode the CDAT table.
> 
> Signed-off-by: Jonathan Cameron <Jonathan.Cameron@...wei.com>
> Co-developed-by: Ira Weiny <ira.weiny@...el.com>
> Signed-off-by: Ira Weiny <ira.weiny@...el.com>
> 
> ---
> Changes from V9:
> 	Add debugging output
> 	Jonathan Cameron
> 		Move read_cdat to port probe by using dev_groups for the
> 		sysfs attributes.  This avoids issues with using devm
> 		before the driver is loaded while making sure the CDAT
> 		binary is available.
> 
> Changes from V8:
> 	Fix length print format
> 	Incorporate feedback from Jonathan
> 	Move all this to cxl_port which can help support switches when
> 	the time comes.
> 
> Changes from V6:
> 	Fix issue with devm use
> 		Move cached cdat data to cxl_dev_state
> 	Use new pci_doe_submit_task()
> 	Ensure the aux driver is locked while processing tasks
> 	Rebased on cxl-pending
> 
> Changes from V5:
> 	Add proper guards around cdat.h
> 	Split out finding the CDAT DOE mailbox
> 	Use cxl_cdat to group CDAT data together
> 	Adjust to use auxiliary_find_device() to find the DOE device
> 		which supplies the CDAT protocol.
> 	Rebased to latest
> 	Remove dev_dbg(length)
> 	Remove unneeded DOE Table access defines
> 	Move CXL_DOE_PROTOCOL_TABLE_ACCESS define into this patch where
> 		it is used
> 
> Changes from V4:
> 	Split this into it's own patch
> 	Rearchitect this such that the memdev driver calls into the DOE
> 	driver via the cxl_mem state object.  This allows CDAT data to
> 	come from any type of cxl_mem object not just PCI DOE.
> 	Rebase on new struct cxl_dev_state
> ---
>  drivers/cxl/cdat.h     |  99 ++++++++++++++++++++++++++++++
>  drivers/cxl/core/pci.c | 136 ++++++++++++++++++++++++++++++++++++++++-
>  drivers/cxl/cxl.h      |   3 +
>  drivers/cxl/cxlpci.h   |   1 +
>  drivers/cxl/port.c     |  50 +++++++++++++++
>  5 files changed, 287 insertions(+), 2 deletions(-)
>  create mode 100644 drivers/cxl/cdat.h
> 
> diff --git a/drivers/cxl/cdat.h b/drivers/cxl/cdat.h
> new file mode 100644
> index 000000000000..f5193a6a51fe
> --- /dev/null
> +++ b/drivers/cxl/cdat.h
> @@ -0,0 +1,99 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +#ifndef __CXL_CDAT_H__
> +#define __CXL_CDAT_H__
> +
> +/*
> + * Coherent Device Attribute table (CDAT)
> + *
> + * Specification available from UEFI.org
> + *
> + * Whilst CDAT is defined as a single table, the access via DOE maiboxes is
> + * done one entry at a time, where the first entry is the header.
> + */
> +
> +#define CXL_DOE_TABLE_ACCESS_REQ_CODE		0x000000ff
> +#define   CXL_DOE_TABLE_ACCESS_REQ_CODE_READ	0
> +#define CXL_DOE_TABLE_ACCESS_TABLE_TYPE		0x0000ff00
> +#define   CXL_DOE_TABLE_ACCESS_TABLE_TYPE_CDATA	0
> +#define CXL_DOE_TABLE_ACCESS_ENTRY_HANDLE	0xffff0000
> +
> +/*
> + * CDAT entries are little endian and are read from PCI config space which
> + * is also little endian.
> + * As such, on a big endian system these will have been reversed.
> + * This prevents us from making easy use of packed structures.
> + * Style form pci_regs.h
> + */
> +
> +#define CDAT_HEADER_LENGTH_DW 4
> +#define CDAT_HEADER_LENGTH_BYTES (CDAT_HEADER_LENGTH_DW * sizeof(u32))
> +#define CDAT_HEADER_DW0_LENGTH		0xffffffff
> +#define CDAT_HEADER_DW1_REVISION	0x000000ff
> +#define CDAT_HEADER_DW1_CHECKSUM	0x0000ff00
> +/* CDAT_HEADER_DW2_RESERVED	*/
> +#define CDAT_HEADER_DW3_SEQUENCE	0xffffffff
> +
> +/* All structures have a common first DW */
> +#define CDAT_STRUCTURE_DW0_TYPE		0x000000ff
> +#define   CDAT_STRUCTURE_DW0_TYPE_DSMAS 0
> +#define   CDAT_STRUCTURE_DW0_TYPE_DSLBIS 1
> +#define   CDAT_STRUCTURE_DW0_TYPE_DSMSCIS 2
> +#define   CDAT_STRUCTURE_DW0_TYPE_DSIS 3
> +#define   CDAT_STRUCTURE_DW0_TYPE_DSEMTS 4
> +#define   CDAT_STRUCTURE_DW0_TYPE_SSLBIS 5
> +
> +#define CDAT_STRUCTURE_DW0_LENGTH	0xffff0000
> +
> +/* Device Scoped Memory Affinity Structure */
> +#define CDAT_DSMAS_DW1_DSMAD_HANDLE	0x000000ff
> +#define CDAT_DSMAS_DW1_FLAGS		0x0000ff00
> +#define CDAT_DSMAS_DPA_OFFSET(entry) ((u64)((entry)[3]) << 32 | (entry)[2])
> +#define CDAT_DSMAS_DPA_LEN(entry) ((u64)((entry)[5]) << 32 | (entry)[4])
> +#define CDAT_DSMAS_NON_VOLATILE(flags)  ((flags & 0x04) >> 2)
> +
> +/* Device Scoped Latency and Bandwidth Information Structure */
> +#define CDAT_DSLBIS_DW1_HANDLE		0x000000ff
> +#define CDAT_DSLBIS_DW1_FLAGS		0x0000ff00
> +#define CDAT_DSLBIS_DW1_DATA_TYPE	0x00ff0000
> +#define CDAT_DSLBIS_BASE_UNIT(entry) ((u64)((entry)[3]) << 32 | (entry)[2])
> +#define CDAT_DSLBIS_DW4_ENTRY_0		0x0000ffff
> +#define CDAT_DSLBIS_DW4_ENTRY_1		0xffff0000
> +#define CDAT_DSLBIS_DW5_ENTRY_2		0x0000ffff
> +
> +/* Device Scoped Memory Side Cache Information Structure */
> +#define CDAT_DSMSCIS_DW1_HANDLE		0x000000ff
> +#define CDAT_DSMSCIS_MEMORY_SIDE_CACHE_SIZE(entry) \
> +	((u64)((entry)[3]) << 32 | (entry)[2])
> +#define CDAT_DSMSCIS_DW4_MEMORY_SIDE_CACHE_ATTRS 0xffffffff
> +
> +/* Device Scoped Initiator Structure */
> +#define CDAT_DSIS_DW1_FLAGS		0x000000ff
> +#define CDAT_DSIS_DW1_HANDLE		0x0000ff00
> +
> +/* Device Scoped EFI Memory Type Structure */
> +#define CDAT_DSEMTS_DW1_HANDLE		0x000000ff
> +#define CDAT_DSEMTS_DW1_EFI_MEMORY_TYPE_ATTR	0x0000ff00
> +#define CDAT_DSEMTS_DPA_OFFSET(entry)	((u64)((entry)[3]) << 32 | (entry)[2])
> +#define CDAT_DSEMTS_DPA_LENGTH(entry)	((u64)((entry)[5]) << 32 | (entry)[4])
> +
> +/* Switch Scoped Latency and Bandwidth Information Structure */
> +#define CDAT_SSLBIS_DW1_DATA_TYPE	0x000000ff
> +#define CDAT_SSLBIS_BASE_UNIT(entry)	((u64)((entry)[3]) << 32 | (entry)[2])
> +#define CDAT_SSLBIS_ENTRY_PORT_X(entry, i) ((entry)[4 + (i) * 2] & 0x0000ffff)
> +#define CDAT_SSLBIS_ENTRY_PORT_Y(entry, i) (((entry)[4 + (i) * 2] & 0xffff0000) >> 16)
> +#define CDAT_SSLBIS_ENTRY_LAT_OR_BW(entry, i) ((entry)[4 + (i) * 2 + 1] & 0x0000ffff)
> +
> +#define CXL_DOE_PROTOCOL_TABLE_ACCESS 2
> +
> +/**
> + * struct cxl_cdat - CXL CDAT data
> + *
> + * @table: cache of CDAT table
> + * @length: length of cached CDAT table
> + */
> +struct cxl_cdat {
> +	void *table;
> +	size_t length;
> +};
> +
> +#endif /* !__CXL_CDAT_H__ */
> diff --git a/drivers/cxl/core/pci.c b/drivers/cxl/core/pci.c
> index d814d8317975..76fa8382b3c7 100644
> --- a/drivers/cxl/core/pci.c
> +++ b/drivers/cxl/core/pci.c
> @@ -9,8 +9,7 @@
>  #include <cxlmem.h>
>  #include <cxl.h>
>  #include "core.h"
> -
> -#define CXL_DOE_PROTOCOL_TABLE_ACCESS 2
> +#include "cdat.h"
>  
>  /**
>   * DOC: cxl core pci
> @@ -493,3 +492,136 @@ void cxl_cache_cdat_mb(struct cxl_port *port)
>  	}
>  }
>  EXPORT_SYMBOL_NS_GPL(cxl_cache_cdat_mb, CXL);
> +
> +#define CDAT_DOE_REQ(entry_handle)					\
> +	(FIELD_PREP(CXL_DOE_TABLE_ACCESS_REQ_CODE,			\
> +		    CXL_DOE_TABLE_ACCESS_REQ_CODE_READ) |		\
> +	 FIELD_PREP(CXL_DOE_TABLE_ACCESS_TABLE_TYPE,			\
> +		    CXL_DOE_TABLE_ACCESS_TABLE_TYPE_CDATA) |		\
> +	 FIELD_PREP(CXL_DOE_TABLE_ACCESS_ENTRY_HANDLE, (entry_handle)))
> +
> +static void cxl_doe_task_complete(struct pci_doe_task *task)
> +{
> +	complete(task->private);
> +}
> +
> +static int cxl_cdat_get_length(struct cxl_port *port, size_t *length)
> +{
> +	u32 cdat_request_pl = CDAT_DOE_REQ(0);
> +	u32 cdat_response_pl[32];
> +	DECLARE_COMPLETION_ONSTACK(c);
> +	struct pci_doe_task task = {
> +		.prot.vid = PCI_DVSEC_VENDOR_ID_CXL,
> +		.prot.type = CXL_DOE_PROTOCOL_TABLE_ACCESS,
> +		.request_pl = &cdat_request_pl,
> +		.request_pl_sz = sizeof(cdat_request_pl),
> +		.response_pl = cdat_response_pl,
> +		.response_pl_sz = sizeof(cdat_response_pl),
> +		.complete = cxl_doe_task_complete,
> +		.private = &c,
> +	};

This is looking like something that could be nicely populated with a macro.

> +	int rc = 0;
> +
> +	if (!port->cdat_mb) {
> +		dev_err(&port->dev, "No CDAT mailbox\n");
> +		return -EIO;
> +	}

AIUI, !port->cdat_mb isn't actually an error. Does it make sense to simply
return 0 here?

> +
> +	rc = pci_doe_submit_task(port->cdat_mb, &task);
> +	if (rc < 0) {
> +		dev_err(&port->dev, "DOE submit failed: %d", rc);
> +		return rc;
> +	}
> +	wait_for_completion(&c);
> +
> +	if (task.rv < 1)
> +		return -EIO;
> +
> +	*length = cdat_response_pl[1];
> +	dev_dbg(&port->dev, "CDAT length %zu\n", *length);
> +
> +	return rc;
> +}
> +
> +static int cxl_cdat_read_table(struct cxl_port *port,
> +			       struct cxl_cdat *cdat)
> +{
> +	size_t length = cdat->length;
> +	u32 *data = cdat->table;
> +	int entry_handle = 0;
> +	int rc = 0;
> +
> +	if (!port->cdat_mb) {
> +		dev_err(&port->dev, "No CDAT mailbox\n");
> +		return -EIO;
> +	}

Similar to above, maybe just return 0?

> +
> +	do {
> +		u32 cdat_request_pl = CDAT_DOE_REQ(entry_handle);
> +		u32 cdat_response_pl[32];
> +		DECLARE_COMPLETION_ONSTACK(c);
> +		struct pci_doe_task task = {
> +			.prot.vid = PCI_DVSEC_VENDOR_ID_CXL,
> +			.prot.type = CXL_DOE_PROTOCOL_TABLE_ACCESS,
> +			.request_pl = &cdat_request_pl,
> +			.request_pl_sz = sizeof(cdat_request_pl),
> +			.response_pl = cdat_response_pl,
> +			.response_pl_sz = sizeof(cdat_response_pl),
> +			.complete = cxl_doe_task_complete,
> +			.private = &c,
> +		};
> +		size_t entry_dw;
> +		u32 *entry;
> +
> +		rc = pci_doe_submit_task(port->cdat_mb, &task);
> +		if (rc < 0) {
> +			dev_err(&port->dev, "DOE submit failed: %d", rc);
> +			return rc;
> +		}
> +		wait_for_completion(&c);

I'd use the timeout variant, but if you don't want to, see below. I can't quite
tell if pci_doe_submit_task() is guaranteed to end with FLAG_DEAD at some
point...

> +
> +		entry = cdat_response_pl + 1;
> +		entry_dw = task.rv / sizeof(u32);
> +		/* Skip Header */
> +		entry_dw -= 1;
> +		entry_dw = min(length / 4, entry_dw);
> +		memcpy(data, entry, entry_dw * sizeof(u32));
> +		length -= entry_dw * sizeof(u32);
> +		data += entry_dw;
> +		entry_handle = FIELD_GET(CXL_DOE_TABLE_ACCESS_ENTRY_HANDLE, cdat_response_pl[0]);

[0] looks suspicious...

> +
> +	} while (entry_handle != 0xFFFF);
> +
> +	return rc;
> +}
> +
> +void read_cdat_data(struct cxl_port *port)

I think you need kdoc here, specifically because you've opted not to do a
timed wait, which means its possible to wait forever.

> +{
> +	struct device *dev = &port->dev;
> +	size_t cdat_length;
> +	int ret;
> +
> +	if (cxl_cdat_get_length(port, &cdat_length))
> +		return;
> +
> +	port->cdat.table = devm_kzalloc(dev, cdat_length, GFP_KERNEL);
> +	if (!port->cdat.table) {
> +		ret = -ENOMEM;
> +		goto error;
> +	}
> +
> +	port->cdat.length = cdat_length;
> +	ret = cxl_cdat_read_table(port, &port->cdat);
> +	if (ret) {
> +		devm_kfree(dev, port->cdat.table);

Usually, when I see devm_kfree, it's a sign that it might not be a good
candidate for devm. You could consider plain kzalloc, and then putting the kfree
in the port destructor. I don't see anything incorrect though, so it's up to
you.

> +		port->cdat.table = NULL;
> +		port->cdat.length = 0;
> +		ret = -EIO;
> +		goto error;
> +	}
> +
> +	return;
> +error:
> +	dev_err(dev, "CDAT data read error (%d)\n", ret);
> +}
> +EXPORT_SYMBOL_NS_GPL(read_cdat_data, CXL);
> diff --git a/drivers/cxl/cxl.h b/drivers/cxl/cxl.h
> index 0a86be589ffc..531b77d296c7 100644
> --- a/drivers/cxl/cxl.h
> +++ b/drivers/cxl/cxl.h
> @@ -8,6 +8,7 @@
>  #include <linux/bitfield.h>
>  #include <linux/bitops.h>
>  #include <linux/io.h>
> +#include "cdat.h"
>  
>  /**
>   * DOC: cxl objects
> @@ -268,6 +269,7 @@ struct cxl_nvdimm {
>   * @dead: last ep has been removed, force port re-creation
>   * @depth: How deep this port is relative to the root. depth 0 is the root.
>   * @cdat_mb: Mailbox which supports the CDAT protocol
> + * @cdat: Cached CDAT data
>   */
>  struct cxl_port {
>  	struct device dev;
> @@ -280,6 +282,7 @@ struct cxl_port {
>  	bool dead;
>  	unsigned int depth;
>  	struct pci_doe_mb *cdat_mb;
> +	struct cxl_cdat cdat;
>  };
>  
>  /**
> diff --git a/drivers/cxl/cxlpci.h b/drivers/cxl/cxlpci.h
> index ddbb8b77752e..71009a167a92 100644
> --- a/drivers/cxl/cxlpci.h
> +++ b/drivers/cxl/cxlpci.h
> @@ -75,4 +75,5 @@ int devm_cxl_port_enumerate_dports(struct cxl_port *port);
>  struct cxl_dev_state;
>  int cxl_hdm_decode_init(struct cxl_dev_state *cxlds, struct cxl_hdm *cxlhdm);
>  void cxl_cache_cdat_mb(struct cxl_port *port);
> +void read_cdat_data(struct cxl_port *port);
>  #endif /* __CXL_PCI_H__ */
> diff --git a/drivers/cxl/port.c b/drivers/cxl/port.c
> index 04f3d1fc6e07..fdff20cf79e6 100644
> --- a/drivers/cxl/port.c
> +++ b/drivers/cxl/port.c
> @@ -50,6 +50,8 @@ static int cxl_port_probe(struct device *dev)
>  		return PTR_ERR(cxlhdm);
>  
>  	cxl_cache_cdat_mb(port);
> +	/* Cache the data early to ensure is_visible() works */
> +	read_cdat_data(port);
>  
>  	if (is_cxl_endpoint(port)) {
>  		struct cxl_memdev *cxlmd = to_cxl_memdev(port->uport);
> @@ -80,10 +82,58 @@ static int cxl_port_probe(struct device *dev)
>  	return 0;
>  }
>  
> +static ssize_t cdat_read(struct file *filp, struct kobject *kobj,
> +			 struct bin_attribute *bin_attr, char *buf,
> +			 loff_t offset, size_t count)
> +{
> +	struct device *dev = kobj_to_dev(kobj);
> +	struct cxl_port *port = to_cxl_port(dev);
> +
> +	if (!port->cdat.table)
> +		return 0;

With visibility setup below, do you need this?

> +
> +	return memory_read_from_buffer(buf, count, &offset,
> +				       port->cdat.table,
> +				       port->cdat.length);
> +}
> +
> +static BIN_ATTR_RO(cdat, 0);
> +
> +static umode_t cxl_port_bin_attr_is_visible(struct kobject *kobj,
> +					      struct bin_attribute *attr, int i)
> +{
> +	struct device *dev = kobj_to_dev(kobj);
> +	struct cxl_port *port = to_cxl_port(dev);
> +
> +	if ((attr == &bin_attr_cdat) && port->cdat.table)
> +		return 0400;
> +
> +	return 0;
> +}
> +
> +static struct bin_attribute *cxl_cdat_bin_attributes[] = {
> +	&bin_attr_cdat,
> +	NULL,
> +};
> +
> +static struct attribute_group cxl_cdat_attribute_group = {
> +	.name = "CDAT",
> +	.bin_attrs = cxl_cdat_bin_attributes,
> +	.is_bin_visible = cxl_port_bin_attr_is_visible,
> +};
> +
> +static const struct attribute_group *cxl_port_attribute_groups[] = {
> +	&cxl_cdat_attribute_group,
> +	NULL,
> +};
> +
>  static struct cxl_driver cxl_port_driver = {
>  	.name = "cxl_port",
>  	.probe = cxl_port_probe,
>  	.id = CXL_DEVICE_PORT,
> +	.drv = {
> +		.dev_groups = cxl_port_attribute_groups,
> +	},
>  };
>  
>  module_cxl_driver(cxl_port_driver);
> -- 
> 2.35.1
> 

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