Re: [RFC PATCH] PCI: Introduce new device binding path using pci_dev.driver_override

Guenter Roeck
2014-04-05T02:07:50Z

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@freescale.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@freescale.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