Re: [PATCH v2 2/7] staging: fsl_-mc: add device binding path 'driver_override'

[Greg KH <gregkh@linuxfoundation.org>]

On Wed, May 06, 2015 at 04:28:23PM -0500, J. German Rivera wrote:
> From: Bharat Bhushan <bharat.bhushan@freescale.com>
> 
> This patch is required for vfio-fsl-mc meta driver to successfully bind
> layerscape container devices for device passthrough. This patch adds
> a mechanism to allow a layerscape device to specify a driver rather than
> a layerscape driver provide a device match.
> 
> This patch is based on following proposed patches for PCI and platform devices
> - https://lkml.org/lkml/2014/4/8/571  :- For Platform devices
> - http://lists-archives.com/linux-kernel/28030441-pci-introduce-new-device-binding-path-using-pci_dev-driver_override.html  :- For PCI devices
> 
> Example to allow a device (dprc.1) to specifically bind
> with driver (vfio-fsl-mc):-
> - echo vfio-fsl-mc > /sys/bus/fsl-mc/devices/dprc.1/driver_override
> - echo dprc.1 > /sys/bus/fsl-mc/drivers/fsl_mc_dprc/unbind
> - echo dprc.1 > /sys/bus/fsl-mc/drivers/vfio-fsl-mc/bind
> 
> Signed-off-by: J. German Rivera <German.Rivera@freescale.com>
> Reviewed-by: Stuart Yoder <stuart.yoder@freescale.com>
> Tested-by: Stuart Yoder <stuart.yoder@freescale.com>
> ---
> Changes in v2:
> none
> 
>  drivers/staging/fsl-mc/bus/mc-bus.c | 67 +++++++++++++++++++++++++++++++++++++
>  drivers/staging/fsl-mc/include/mc.h |  2 ++
>  2 files changed, 69 insertions(+)
> 
> diff --git a/drivers/staging/fsl-mc/bus/mc-bus.c b/drivers/staging/fsl-mc/bus/mc-bus.c
> index d51120a..0e9cba8 100644
> --- a/drivers/staging/fsl-mc/bus/mc-bus.c
> +++ b/drivers/staging/fsl-mc/bus/mc-bus.c
> @@ -58,6 +58,12 @@ static int fsl_mc_bus_match(struct device *dev, struct device_driver *drv)
>  	if (WARN_ON(!fsl_mc_bus_type.dev_root))
>  		goto out;
> 
> +	/* When driver_override is set, only bind to the matching driver */
> +	if (mc_dev->driver_override) {
> +		found = !strcmp(mc_dev->driver_override, mc_drv->driver.name);
> +		goto out;
> +	}
> +
>  	if (!mc_drv->match_id_table)
>  		goto out;
> 
> @@ -116,10 +122,69 @@ static int fsl_mc_bus_uevent(struct device *dev, struct kobj_uevent_env *env)
>  	return 0;
>  }
> 
> +static ssize_t driver_override_store(struct device *dev,
> +				     struct device_attribute *attr,
> +				     const char *buf, size_t count)
> +{
> +	struct fsl_mc_device *mc_dev = to_fsl_mc_device(dev);
> +	const char *driver_override, *old = mc_dev->driver_override;
> +	char *cp;
> +
> +	if (WARN_ON(dev->bus != &fsl_mc_bus_type))
> +		return -EINVAL;
> +
> +	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)) {
> +		mc_dev->driver_override = driver_override;
> +	} else {
> +		kfree(driver_override);
> +		mc_dev->driver_override = NULL;
> +	}
> +
> +	kfree(old);
> +
> +	return count;
> +}
> +
> +static ssize_t driver_override_show(struct device *dev,
> +				    struct device_attribute *attr, char *buf)
> +{
> +	struct fsl_mc_device *mc_dev = to_fsl_mc_device(dev);
> +
> +	return sprintf(buf, "%s\n", mc_dev->driver_override);
> +}
> +
> +static DEVICE_ATTR_RW(driver_override);

Documenation for this new sysfs attribute?

> +
> +static struct attribute *fsl_mc_dev_attrs[] = {
> +	&dev_attr_driver_override.attr,
> +	NULL,
> +};
> +
> +static const struct attribute_group fsl_mc_dev_group = {
> +	.attrs = fsl_mc_dev_attrs,
> +};
> +
> +static const struct attribute_group *fsl_mc_dev_groups[] = {
> +	&fsl_mc_dev_group,
> +	NULL,
> +};

ATTRIBUTE_GROUP()?