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Date:	Thu, 23 Oct 2014 16:36:52 +0300
From:	Marcel Apfelbaum <marcel.a@...hat.com>
To:	Alex Williamson <alex.williamson@...hat.com>
Cc:	linux-pci@...r.kernel.org, bhelgaas@...gle.com,
	linux-kernel@...r.kernel.org, marcel@...hat.com, mst@...hat.com,
	Stuart Yoder <stuart.yoder@...escale.com>
Subject: Re: [PATCH v4] PCI: add kernel parameter to override devid<->driver
 mapping.

On Thu, 2014-10-23 at 07:11 -0600, Alex Williamson wrote:
> On Thu, 2014-10-23 at 15:32 +0300, Marcel Apfelbaum wrote:
> > On Wed, 2014-10-22 at 12:32 -0600, Alex Williamson wrote:
> > > [cc+ stuart]
> > > 
> > > On Mon, 2014-10-20 at 17:04 +0300, Marcel Apfelbaum wrote:
> > > > Scanning a lot of devices during boot requires a lot of time.
> > > > On other scenarios there is a need to bind a driver to a specific slot.
> > > > 
> > > > Binding devices to pci-stub driver does not work,
> > > > as it will not differentiate between devices of the
> > > > same type. Using some start scripts is error prone.
> > > > 
> > > > The solution leverages driver_override functionality introduced by
> > > > 
> > > > 	commit: 782a985d7af26db39e86070d28f987cad21313c0
> > > > 	Author: Alex Williamson <alex.williamson@...hat.com>
> > > > 	Date:   Tue May 20 08:53:21 2014 -0600
> > > > 
> > > >     	PCI: Introduce new device binding path using pci_dev.driver_override
> > > > 
> > > > In order to bind PCI slots to specific drivers use:
> > > > 	pci=driver[xxxx:xx:xx.x]=foo,driver[xxxx:xx:xx.x]=bar,...
> > > > 
> > > > Signed-off-by: Marcel Apfelbaum <marcel.a@...hat.com>
> > > > ---
> > > > v3 -> v4:
> > > >  - Addressed Alex Williamson's comments:
> > > >    - Modified the type of driver_override_entry's fields
> > > >    - Used PCI_DEVFN when appropriated
> > > >    - Removed redundant checks
> > > >    - Replaced BUG_ON with pr_err messages
> > > >    - Simpler command line parsing
> > > >  - Addressed Michael S. Tsirkin comments
> > > >    - removed DRIVER_OVERRIDE_NAME_LENGTH limitation
> > > > v2 -> v3:
> > > >  - Corrected subject line
> > > > v1 -> v2:
> > > >  - Addressed Michael S. Tsirkin comments
> > > >    - Removed 32 slots limitation
> > > >    - Better handling of memory allocation failures
> > > >      (preferred BUG_ON over error messages)
> > > >  - Addressed Alex Williamson's comments:
> > > >    - Modified commit message to show parameter usage more clear.
> > > >  - I preferred to re-use parse_args instead of manually using
> > > >    strstr in order to better comply with command line parsing
> > > >    rules.
> > > >  - I didn't use any locking when parsing the command line args
> > > >    (see parse_done usage) assuming that first call will be
> > > >    early in system boot and no race can occur. Please correct
> > > >    me if I am wrong.
> > > > 
> > > > Notes:
> > > >  - I have further ideas on top of this patch based on your reviews.
> > > >    I thought of:
> > > >    - Use wildcards to specify entire buses/devices, something like:
> > > >      	driver[0001:02:*.*]=pci-stub
> > > >    - Use comma to separate several devices:
> > > >      	driver[0001:02:03.4,0001:02:04.0,...]=pci-stub
> > > >    - Make domain optional:
> > > >    	driver[00:03.0]=pci-stub
> > > > 
> > > > Comments will be appreciated,
> > > > Thanks,
> > > > Marcel
> > > >  Documentation/kernel-parameters.txt |   4 ++
> > > >  drivers/pci/bus.c                   | 111 ++++++++++++++++++++++++++++++++++++
> > > >  drivers/pci/pci.c                   |   2 +
> > > >  3 files changed, 117 insertions(+)
> > > 
> > > The driver_override feature that we're making use of here is also going
> > > to be supported by platform devices and potentially more bustypes in the
> > > future, so I'm concerned that making a pci specific kernel parameter is
> > > too shortsighted.  Instead we could hook on to BUS_NOTIFY_ADD_DEVICE for
> > > bustypes that support driver_override so we can have a common interface.
> > The real question here if those bus types/devices would benefit from this
> > feature, and I also must confess that I have no knowledge of the other buses.
> > Can anyone confirm that it does make sense for them?
> 
> Platform devices are adding vfio support, so I expect the next logical
> question will be how to reserve devices for use by vfio at boot.
Well, I'll have to learn more about vfio before saying anything,
but my question is if it can be deferred or it has to be part of
this patch. If the platform devices do not have a slot like hw address, 
maybe it can be configured separately.

I saw this patch as a PCI patch, and not "driver_override" expansion;
meaning that I only leveraged an existing feature, not trying to
extend it.
If I am wrong, please point me to a more robust solution.


> 
> > > Perhaps:
> > > 
> > > driver_override=pci,0000:02:00.0=pci-stub;platform,fakename=vfio-platform
> > > 
> > > Finding delimiters that don't conflict may be challenging.  Also, can we
> > > assume that bus-name:dev-name is unique for every bustype?  It is for
> > > pci, platform?
> > For PCI, sure the domain:bus:dev.func is unique, for platform I have no idea,
> > can anyone that knows "platform" confirm or deny?
> > 
> > > 
> > > It also seems like there's a question of how long should this override
> > > last and how does the user disable it?  
> > > I think with pci-stub.ids=
> > > $VENDOR:$DEVICE a user can echo the IDs to the pci-stub/remove_id sysfs
> > > entry to cancel the effect.
> > The way I see it is simple, the override specified in kernel command line
> > last as long as the user does not specifically remove it using
> > echo "" > /sys/.../driver_override
> > and then unbind and bind the device again.
> > 
> > >   The only option here seems to be a reboot.
> > Please see above
> 
> That's only a temporary removal though, if the device is removed and
> re-added, either via physical hotplug or sysfs, the override is
> re-applied.  Thanks,
Bear with me please,

If we empty the driver_override file (cat "" /sys/bus/.../slot/driver_override)
as suggested above, the override will not be reapplied.

So, it is a consistent model:
1. The end-user specified the driver in command-line, so he wants it there
   even after unbinding/binding or hotplug operations.
2. If the end-user "changes his mind", he doesn't need to reboot the system,
   only to clear the driver_override sysfs file and from this moment on
   the system behaves like usual. (at next unbind/bind or hotplug)

I hope I got it right,
Thanks,
Marcel


> 
> Alex
> 
> > > Do we need a /sys/bus/pci/driver_overrides/{add_name,remove_name} for
> > > this interface?  Thanks,
> > While it does not hurt, I see it as optional since a simple removal of
> > driver_override and rebind does the same
> > 
> > Thanks,
> > Marcel
> > 
> > > 
> > > Alex
> > > 
> > > > diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
> > > > index 5ae8608..c1cbb4c 100644
> > > > --- a/Documentation/kernel-parameters.txt
> > > > +++ b/Documentation/kernel-parameters.txt
> > > > @@ -2631,6 +2631,10 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
> > > >  		pcie_scan_all	Scan all possible PCIe devices.  Otherwise we
> > > >  				only look for one device below a PCIe downstream
> > > >  				port.
> > > > +		driver		Provide an override to the devid<->driver mapping
> > > > +				for a specific slot.
> > > > +				Bind PCI slot 0001:02:03.4 to pci-stub by:
> > > > +					driver[0001:02:03.4]=pci-stub
> > > >  
> > > >  	pcie_aspm=	[PCIE] Forcibly enable or disable PCIe Active State Power
> > > >  			Management.
> > > > diff --git a/drivers/pci/bus.c b/drivers/pci/bus.c
> > > > index 73aef51..b49f5cc 100644
> > > > --- a/drivers/pci/bus.c
> > > > +++ b/drivers/pci/bus.c
> > > > @@ -15,6 +15,8 @@
> > > >  #include <linux/proc_fs.h>
> > > >  #include <linux/slab.h>
> > > >  
> > > > +#include <asm/setup.h>
> > > > +
> > > >  #include "pci.h"
> > > >  
> > > >  void pci_add_resource_offset(struct list_head *resources, struct resource *res,
> > > > @@ -230,6 +232,114 @@ EXPORT_SYMBOL(pci_bus_alloc_resource);
> > > >  
> > > >  void __weak pcibios_resource_survey_bus(struct pci_bus *bus) { }
> > > >  
> > > > +struct driver_override_entry {
> > > > +	u16 domain;
> > > > +	u8 bus;
> > > > +	u8 devfn;
> > > > +	char *driver_name;
> > > > +	struct list_head list;
> > > > +};
> > > > +
> > > > +static LIST_HEAD(driver_override_entries);
> > > > +
> > > > +static int pci_device_parse_driver_override(char *param, char *val,
> > > > +					    const char *unused)
> > > > +{
> > > > +	unsigned int domain, bus, dev, fn;
> > > > +	char  *buf;
> > > > +	struct driver_override_entry *entry;
> > > > +	int ret;
> > > > +
> > > > +	buf = kmalloc(COMMAND_LINE_SIZE, GFP_KERNEL);
> > > > +	if (!buf)
> > > > +		goto err_buf;
> > > > +
> > > > +	while (val) {
> > > > +		char *k = strchr(val, ',');
> > > > +
> > > > +		if (k)
> > > > +			*k++ = 0;
> > > > +
> > > > +		if (strncmp(val, "driver", 6)) {
> > > > +			val = k;
> > > > +			continue;
> > > > +		}
> > > > +
> > > > +		memset(buf, 0, COMMAND_LINE_SIZE);
> > > > +		ret = sscanf(val + 6, "[%4x:%2x:%2x.%2x]=%s",
> > > > +			     &domain, &bus, &dev, &fn, buf);
> > > > +		if (ret != 5) {
> > > > +			pr_warn("PCI: Invalid command line: %s\n", val);
> > > > +			val = k;
> > > > +			continue;
> > > > +		}
> > > > +
> > > > +		entry = kzalloc(sizeof(*entry), GFP_KERNEL);
> > > > +		if (!entry)
> > > > +			goto err_entry;
> > > > +
> > > > +		INIT_LIST_HEAD(&entry->list);
> > > > +		entry->domain = domain;
> > > > +		entry->bus = bus;
> > > > +		entry->devfn = PCI_DEVFN(dev, fn);
> > > > +		entry->driver_name = kstrdup(buf, GFP_KERNEL);
> > > > +		if (!entry->driver_name)
> > > > +			goto err_driver_name;
> > > > +
> > > > +		list_add_tail(&entry->list, &driver_override_entries);
> > > > +		val = k;
> > > > +	}
> > > > +
> > > > +	kfree(buf);
> > > > +	return 0;
> > > > +
> > > > +err_driver_name:
> > > > +	kfree(entry);
> > > > +
> > > > +err_entry:
> > > > +	kfree(buf);
> > > > +
> > > > +err_buf:
> > > > +	pr_err("PCI: Out of memory while parsing command line: %s\n", val);
> > > > +	return -ENOMEM;
> > > > +}
> > > > +
> > > > +static void pci_device_setup_driver_override(struct pci_dev *dev)
> > > > +{
> > > > +	static int parse_done;
> > > > +	struct driver_override_entry *entry;
> > > > +
> > > > +	if (!parse_done) {
> > > > +		char *cmdline = kstrdup(saved_command_line, GFP_KERNEL);
> > > > +
> > > > +		if (!cmdline)
> > > > +			goto err_out_of_mem;
> > > > +
> > > > +		parse_args("pci", cmdline, NULL,
> > > > +			   0, 0, 0, &pci_device_parse_driver_override);
> > > > +		kfree(cmdline);
> > > > +		parse_done = 1;
> > > > +	}
> > > > +
> > > > +	list_for_each_entry(entry, &driver_override_entries, list) {
> > > > +		if (pci_domain_nr(dev->bus) != entry->domain ||
> > > > +		    dev->bus->number != entry->bus ||
> > > > +		    dev->devfn != entry->devfn)
> > > > +			continue;
> > > > +
> > > > +		dev->driver_override = kstrdup(entry->driver_name, GFP_KERNEL);
> > > > +		if (!dev->driver_override)
> > > > +			goto err_out_of_mem;
> > > > +
> > > > +		break;
> > > > +	}
> > > > +
> > > > +	return;
> > > > +
> > > > +err_out_of_mem:
> > > > +	pr_err("PCI: Out of memory while setting up driver override\n");
> > > > +}
> > > > +
> > > >  /**
> > > >   * pci_bus_add_device - start driver for a single device
> > > >   * @dev: device to add
> > > > @@ -245,6 +355,7 @@ void pci_bus_add_device(struct pci_dev *dev)
> > > >  	 * are not assigned yet for some devices.
> > > >  	 */
> > > >  	pci_fixup_device(pci_fixup_final, dev);
> > > > +	pci_device_setup_driver_override(dev);
> > > >  	pci_create_sysfs_dev_files(dev);
> > > >  	pci_proc_attach_device(dev);
> > > >  
> > > > diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
> > > > index 625a4ac..37809d4 100644
> > > > --- a/drivers/pci/pci.c
> > > > +++ b/drivers/pci/pci.c
> > > > @@ -4508,6 +4508,8 @@ static int __init pci_setup(char *str)
> > > >  				pcie_bus_config = PCIE_BUS_PEER2PEER;
> > > >  			} else if (!strncmp(str, "pcie_scan_all", 13)) {
> > > >  				pci_add_flags(PCI_SCAN_ALL_PCIE_DEVS);
> > > > +			} else if (!strncmp(str, "driver", 6)) {
> > > > +				/* lazy evaluation by the pci subsystem */
> > > >  			} else {
> > > >  				printk(KERN_ERR "PCI: Unknown option `%s'\n",
> > > >  						str);
> > > 
> > > 
> > > 
> > 
> > 
> > 
> 
> 
> 
> 



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