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Date: Thu, 29 May 2014 13:43:39 -0600
From: Alex Williamson <alex.williamson@...hat.com>
To: Kim Phillips <kim.phillips@...aro.org>
Cc: a.motakis@...tualopensystems.com, kvmarm@...ts.cs.columbia.edu,
iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org,
kvm@...r.kernel.org, linux-doc@...r.kernel.org,
gregkh@...uxfoundation.org, jhovold@...il.com, will.deacon@....com,
a.rigo@...tualopensystems.com, rob.herring@...xeda.com,
stuart.yoder@...escale.com, rob@...dley.net,
grant.likely@...aro.org, tech@...tualopensystems.com,
clbchenlibo.chen@...wei.com, christoffer.dall@...aro.org,
eric.auger@...aro.org, Julien Grall <julien.grall@...aro.org>,
Ian Campbell <ian.campbell@...rix.com>,
Stefano Stabellini <stefano.stabellini@...citrix.com>,
Alexander Graf <agraf@...e.de>
Subject: Re: [RFC PATCH v5_v2 01/11] driver core: platform: add device
binding path 'driver_override'
On Tue, 2014-05-20 at 19:25 -0500, Kim Phillips wrote:
> From: Kim Phillips <kim.phillips@...escale.com>
>
> Needed by platform device drivers, such as the vfio-platform driver
> later in series, 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" [1], which is an interface enhancement
> for more deterministic PCI device binding, e.g., when in the
> presence of hotplug.
>
> [1] https://lists.cs.columbia.edu/pipermail/kvmarm/2014-May/009527.html
>
> Suggested-by: Alex Williamson <alex.williamson@...hat.com>
> Signed-off-by: Kim Phillips <kim.phillips@...escale.com>
Looks largely identical to the PCI version of the same that has been
accepted for v3.16 and ack'd by GregKH.
Reviewed-by: Alex Williamson <alex.williamson@...hat.com>
> ---
> changes in v2 patch of v5 of this patchseries:
> - rebased onto today's Linus' ToT
> - added kfree to match PCI counterpart fix, as Alex Williamson
> just posted a v3 of the patch (thanks Christoffer for the
> notification)
> - in the commit text, replaced vfio platform driver reference with
> 'later in series', and updated the PCI version mailing list reference
> to the v3 version.
>
> Is it safe to assume this patch will continue to as part of the VFIO
> platform driver patchseries, and be submitted by Antonis? If so, can
> we start collecting some {Reviewed,Acked}-bys? Thanks, Kim.
>
> Documentation/ABI/testing/sysfs-bus-platform | 20 ++++++++++++
> drivers/base/platform.c | 47 ++++++++++++++++++++++++++++
> include/linux/platform_device.h | 1 +
> 3 files changed, 68 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..5172a61
> --- /dev/null
> +++ b/Documentation/ABI/testing/sysfs-bus-platform
> @@ -0,0 +1,20 @@
> +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 is specified by writing a string
> + to the driver_override file (echo vfio-platform > \
> + driver_override) and may be cleared with an empty string
> + (echo > driver_override). This returns 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. If no
> + driver with a matching name is currently loaded in the kernel,
> + the device will not bind to any driver. This also allows
> + devices to opt-out of driver binding using a driver_override
> + name such as "none". Only a single driver may be specified in
> + the override, there is no support for parsing delimiters.
> diff --git a/drivers/base/platform.c b/drivers/base/platform.c
> index 5b47210..4f47563 100644
> --- a/drivers/base/platform.c
> +++ b/drivers/base/platform.c
> @@ -23,6 +23,7 @@
> #include <linux/pm_runtime.h>
> #include <linux/idr.h>
> #include <linux/acpi.h>
> +#include <linux/limits.h>
>
> #include "base.h"
> #include "power/power.h"
> @@ -188,6 +189,7 @@ static void platform_device_release(struct device *dev)
> kfree(pa->pdev.dev.platform_data);
> kfree(pa->pdev.mfd_cell);
> kfree(pa->pdev.resource);
> + kfree(pa->pdev.driver_override);
> kfree(pa);
> }
>
> @@ -695,8 +697,49 @@ 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, *cp;
> +
> + if (count > PATH_MAX)
> + return -EINVAL;
> +
> + driver_override = kstrndup(buf, count, GFP_KERNEL);
> + if (!driver_override)
> + return -ENOMEM;
> +
> + cp = strchr(driver_override, '\n');
> + if (cp)
> + *cp = '\0';
> +
> + if (strlen(driver_override)) {
> + pdev->driver_override = driver_override;
> + } else {
> + kfree(driver_override);
> + pdev->driver_override = NULL;
> + }
> +
> + kfree(old);
> +
> + return count;
> +}
> +
> +static ssize_t driver_override_show(struct device *dev,
> + struct device_attribute *attr, char *buf)
> +{
> + struct platform_device *pdev = to_platform_device(dev);
> +
> + return sprintf(buf, "%s\n", pdev->driver_override);
> +}
> +static DEVICE_ATTR_RW(driver_override);
> +
> +
> static struct attribute *platform_dev_attrs[] = {
> &dev_attr_modalias.attr,
> + &dev_attr_driver_override.attr,
> NULL,
> };
> ATTRIBUTE_GROUPS(platform_dev);
> @@ -752,6 +795,10 @@ static int platform_match(struct device *dev, struct device_driver *drv)
> struct platform_device *pdev = to_platform_device(dev);
> struct platform_driver *pdrv = to_platform_driver(drv);
>
> + /* When driver_override is set, only bind to the matching driver */
> + if (pdev->driver_override)
> + return !strcmp(pdev->driver_override, drv->name);
> +
> /* Attempt an OF style match first */
> if (of_driver_match_device(dev, drv))
> return 1;
> diff --git a/include/linux/platform_device.h b/include/linux/platform_device.h
> index 16f6654..153d303 100644
> --- a/include/linux/platform_device.h
> +++ b/include/linux/platform_device.h
> @@ -28,6 +28,7 @@ struct platform_device {
> struct resource *resource;
>
> const struct platform_device_id *id_entry;
> + char *driver_override; /* Driver name to force a match */
>
> /* MFD cell pointer */
> struct mfd_cell *mfd_cell;
--
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