linux-kernel - Re: [RFC PATCH] PCI: Introduce new device binding path using pci_dev.driver

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Date:	Fri, 04 Apr 2014 19:07:29 -0700
From:	Guenter Roeck <linux@...ck-us.net>
To:	Kim Phillips <kim.phillips@...escale.com>,
	Alex Williamson <alex.williamson@...hat.com>
CC:	Kim Phillips <kim.phillips@...aro.org>, gregkh@...uxfoundation.org,
	stuart.yoder@...escale.com, kvm@...r.kernel.org,
	jan.kiszka@...mens.com, will.deacon@....com,
	linux-kernel@...r.kernel.org, mhocko@...e.cz, bhelgaas@...gle.com,
	Varun.Sethi@...escale.com, kvmarm@...ts.cs.columbia.edu,
	rafael.j.wysocki@...el.com, agraf@...e.de,
	linux-pci@...r.kernel.org, konrad.wilk@...cle.com,
	d.kasatkin@...sung.com, tj@...nel.org, scottwood@...escale.com,
	a.motakis@...tualopensystems.com, tech@...tualopensystems.com,
	Bharat.Bhushan@...escale.com, toshi.kani@...com,
	a.rigo@...tualopensystems.com, iommu@...ts.linux-foundation.org,
	joe@...ches.com, christoffer.dall@...aro.org
Subject: Re: [RFC PATCH] PCI: Introduce new device binding path using pci_dev.driver_override

On 04/04/2014 06:35 PM, Kim Phillips wrote:
> Needed by platform device drivers, such as the vfio-platform driver [1],
> in order to bypass the existing OF, ACPI, id_table and name string matches,
> and successfully be able to be bound to any device, like so:
>
> echo vfio-platform > /sys/bus/platform/devices/fff51000.ethernet/driver_override
> echo fff51000.ethernet > /sys/bus/platform/devices/fff51000.ethernet/driver/unbind
> echo fff51000.ethernet > /sys/bus/platform/drivers_probe
>
> This mimics "PCI: Introduce new device binding path using
> pci_dev.driver_override" [2], which is an interface enhancement
> for more deterministic PCI device binding, e.g., when in the
> presence of hotplug.
>
> [1] http://lkml.iu.edu/hypermail/linux/kernel/1402.1/00177.html
> [2] http://thread.gmane.org/gmane.linux.kernel.iommu/4605
>
> Signed-off-by: Kim Phillips <kim.phillips@...escale.com>
> ---
> if this looks ok, should it be included in the next version of the
> vfio-platform submission series, like last time ([1] above)?
>
>   Documentation/ABI/testing/sysfs-bus-platform | 17 ++++++++++
>   drivers/base/platform.c                      | 46 ++++++++++++++++++++++++++++
>   include/linux/platform_device.h              |  1 +
>   3 files changed, 64 insertions(+)
>   create mode 100644 Documentation/ABI/testing/sysfs-bus-platform
>
> diff --git a/Documentation/ABI/testing/sysfs-bus-platform b/Documentation/ABI/testing/sysfs-bus-platform
> new file mode 100644
> index 0000000..6b14a6a
> --- /dev/null
> +++ b/Documentation/ABI/testing/sysfs-bus-platform
> @@ -0,0 +1,17 @@
> +What:		/sys/bus/platform/devices/.../driver_override
> +Date:		April 2014
> +Contact:	Kim Phillips <kim.phillips@...escale.com>
> +Description:
> +		This file allows the driver for a device to be specified
> +		which will override standard OF, ACPI, ID table, and name
> +		matching.  When specified, only a driver with a name matching
> +		the value written to driver_override will have an opportunity
> +		to bind to the device.  The override may be cleared by
> +		writing an empty string (ex. echo > driver_override), returning
> +		the device to standard matching rules binding.  Writing to
> +		driver_override does not automatically unbind the device from
> +		its current driver or make any attempt to automatically load
> +		the specified driver name.  If no driver with a matching name
> +		is currently loaded in the kernel, no match will be found.
> +		This also allows devices to opt-out of driver binding using
> +		a driver_override name such as "none".
> diff --git a/drivers/base/platform.c b/drivers/base/platform.c
> index e714709..ded1db1 100644
> --- a/drivers/base/platform.c
> +++ b/drivers/base/platform.c
> @@ -22,6 +22,7 @@
>   #include <linux/pm_runtime.h>
>   #include <linux/idr.h>
>   #include <linux/acpi.h>
> +#include <linux/limits.h>
>
>   #include "base.h"
>   #include "power/power.h"
> @@ -690,8 +691,49 @@ static ssize_t modalias_show(struct device *dev, struct device_attribute *a,
>   }
>   static DEVICE_ATTR_RO(modalias);
>
> +static ssize_t driver_override_store(struct device *dev,
> +				     struct device_attribute *attr,
> +				     const char *buf, size_t count)
> +{
> +	struct platform_device *pdev = to_platform_device(dev);
> +	char *driver_override, *old = pdev->driver_override;
> +
> +	if (count > PATH_MAX)
> +		return -EINVAL;
> +
> +	driver_override = kstrndup(buf, count, GFP_KERNEL);
> +	if (!driver_override)
> +		return -ENOMEM;
> +
> +	while (strlen(driver_override) &&
> +	       driver_override[strlen(driver_override) - 1] == '\n')
> +		driver_override[strlen(driver_override) - 1] = '\0';
> +

Seems to me that something like

	cp = strchr(driver_override, '\n');
	if (cp)
		*cp = '\0';

would be much simpler.

Guenter

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