Re: [PATCH 1/2] fpga: dfl: add driver_override support

[Tom Rix]

On 10/15/20 11:02 PM, Xu Yilun wrote:
> Add support for overriding the default matching of a dfl device to a dfl
> driver. It follows the same way that can be used for PCI and platform
> devices. This patch adds the 'driver_override' sysfs file.
>
> Signed-off-by: Xu Yilun <yilun.xu@xxxxxxxxx>
> ---
>  Documentation/ABI/testing/sysfs-bus-dfl | 28 ++++++++++++++---
>  drivers/fpga/dfl.c                      | 54 ++++++++++++++++++++++++++++++++-
>  include/linux/dfl.h                     |  2 ++
>  3 files changed, 79 insertions(+), 5 deletions(-)
>
> diff --git a/Documentation/ABI/testing/sysfs-bus-dfl b/Documentation/ABI/testing/sysfs-bus-dfl
> index 23543be..db7e8d3 100644
> --- a/Documentation/ABI/testing/sysfs-bus-dfl
> +++ b/Documentation/ABI/testing/sysfs-bus-dfl
> @@ -1,15 +1,35 @@
>  What:		/sys/bus/dfl/devices/dfl_dev.X/type
> -Date:		Aug 2020
> -KernelVersion:	5.10
> +Date:		Oct 2020
> +KernelVersion:	5.11
>  Contact:	Xu Yilun <yilun.xu@xxxxxxxxx>
>  Description:	Read-only. It returns type of DFL FIU of the device. Now DFL
>  		supports 2 FIU types, 0 for FME, 1 for PORT.
>  		Format: 0x%x
>  
>  What:		/sys/bus/dfl/devices/dfl_dev.X/feature_id
> -Date:		Aug 2020
> -KernelVersion:	5.10
> +Date:		Oct 2020
> +KernelVersion:	5.11
>  Contact:	Xu Yilun <yilun.xu@xxxxxxxxx>
>  Description:	Read-only. It returns feature identifier local to its DFL FIU
>  		type.
>  		Format: 0x%x

These updates, do not match the comment.

Consider splitting this out.

> +
> +What:           /sys/bus/dfl/devices/.../driver_override
> +Date:           Oct 2020
> +KernelVersion:  5.11
> +Contact:        Xu Yilun <yilun.xu@xxxxxxxxx>
I am looking at description and trying to make it consistent with sysfs-bus-pci
> +Description:    This file allows the driver for a device to be specified.

'to be specified which will override the standard dfl bus feature id to driver mapping.'


>  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 dfl-uio-pdev > 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/fpga/dfl.c b/drivers/fpga/dfl.c
> index 511b20f..bc35750 100644
> --- a/drivers/fpga/dfl.c
> +++ b/drivers/fpga/dfl.c
> @@ -262,6 +262,10 @@ static int dfl_bus_match(struct device *dev, struct device_driver *drv)
>  	struct dfl_driver *ddrv = to_dfl_drv(drv);
>  	const struct dfl_device_id *id_entry;
>  
> +	/* When driver_override is set, only bind to the matching driver */
> +	if (ddev->driver_override)
> +		return !strcmp(ddev->driver_override, drv->name);
> +
>  	id_entry = ddrv->id_table;
>  	if (id_entry) {
>  		while (id_entry->feature_id) {
> @@ -303,6 +307,53 @@ static int dfl_bus_uevent(struct device *dev, struct kobj_uevent_env *env)
>  			      ddev->type, ddev->feature_id);
>  }
>  

I am looking at other implementations of driver_override* and looking for consistency.

> +static ssize_t driver_override_show(struct device *dev,
> +				    struct device_attribute *attr, char *buf)
> +{
> +	struct dfl_device *ddev = to_dfl_dev(dev);
> +	ssize_t len;
> +
> +	device_lock(dev);
> +	len = sprintf(buf, "%s\n", ddev->driver_override);
len = snprintf(buf, PAGE_SIZE ...
> +	device_unlock(dev);
> +	return len;
> +}
> +
> +static ssize_t driver_override_store(struct device *dev,
> +				     struct device_attribute *attr,
> +				     const char *buf, size_t count)
> +{
> +	struct dfl_device *ddev = to_dfl_dev(dev);
> +	char *driver_override, *old, *cp;
> +
> +	/* We need to keep extra room for a newline */
> +	if (count >= (PAGE_SIZE - 1))
> +		return -EINVAL;
> +
> +	driver_override = kstrndup(buf, count, GFP_KERNEL);
> +	if (!driver_override)
> +		return -ENOMEM;
> +
> +	cp = strchr(driver_override, '\n');
> +	if (cp)
> +		*cp = '\0';
> +
> +	device_lock(dev);
> +	old = ddev->driver_override;
> +	if (strlen(driver_override)) {
> +		ddev->driver_override = driver_override;
> +	} else {
> +		kfree(driver_override);
> +		ddev->driver_override = NULL;
> +	}
> +	device_unlock(dev);
> +
> +	kfree(old);
> +
> +	return count;
> +}
> +static DEVICE_ATTR_RW(driver_override);
> +
>  static ssize_t
>  type_show(struct device *dev, struct device_attribute *attr, char *buf)
>  {
> @@ -324,6 +375,7 @@ static DEVICE_ATTR_RO(feature_id);
>  static struct attribute *dfl_dev_attrs[] = {
>  	&dev_attr_type.attr,
>  	&dev_attr_feature_id.attr,
> +	&dev_attr_driver_override.attr,
>  	NULL,
>  };
>  ATTRIBUTE_GROUPS(dfl_dev);
> @@ -469,7 +521,7 @@ static int dfl_devs_add(struct dfl_feature_platform_data *pdata)
>  
>  int __dfl_driver_register(struct dfl_driver *dfl_drv, struct module *owner)
>  {
> -	if (!dfl_drv || !dfl_drv->probe || !dfl_drv->id_table)
> +	if (!dfl_drv || !dfl_drv->probe)

id_table is still needed for the normal case.

Instead of removing this check, could you add something like

|| (!dfl_drv->is_override && !dfl_drv->id_table)

Tom

>  		return -EINVAL;
>  
>  	dfl_drv->drv.owner = owner;
> diff --git a/include/linux/dfl.h b/include/linux/dfl.h
> index 7affba2f..e1b2471 100644
> --- a/include/linux/dfl.h
> +++ b/include/linux/dfl.h
> @@ -32,6 +32,7 @@ enum dfl_id_type {
>   * @num_irqs: number of IRQs supported by this dfl device.
>   * @cdev: pointer to DFL FPGA container device this dfl device belongs to.
>   * @id_entry: matched id entry in dfl driver's id table.
> + * @driver_override: driver name to force a match
>   */
>  struct dfl_device {
>  	struct device dev;
> @@ -43,6 +44,7 @@ struct dfl_device {
>  	unsigned int num_irqs;
>  	struct dfl_fpga_cdev *cdev;
>  	const struct dfl_device_id *id_entry;
> +	char *driver_override;
>  };
>  
>  /**