Re: [RFC PATCH v2 1/3] drivers/accel: define kconfig and register a new major

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

On Wed, Nov 02, 2022 at 10:34:03PM +0200, Oded Gabbay wrote:
> --- /dev/null
> +++ b/drivers/accel/Kconfig
> @@ -0,0 +1,24 @@
> +# SPDX-License-Identifier: GPL-2.0-only
> +#
> +# Compute Acceleration device configuration
> +#
> +# This framework provides support for compute acceleration devices, such
> +# as, but not limited to, Machine-Learning and Deep-Learning acceleration
> +# devices
> +#
> +menuconfig ACCEL
> +	tristate "Compute Acceleration Framework"
> +	depends on DRM
> +	help
> +	  Framework for device drivers of compute acceleration devices, such
> +	  as, but not limited to, Machine-Learning and Deep-Learning
> +	  acceleration devices.
> +	  If you say Y here, you need to select the module that's right for
> +	  your acceleration device from the list below.
> +	  This framework is integrated with the DRM subsystem as compute
> +	  accelerators and GPUs share a lot in common and can use almost the
> +	  same infrastructure code.
> +	  Having said that, acceleration devices will have a different
> +	  major number than GPUs, and will be exposed to user-space using
> +	  different device files, called accel/accel* (in /dev, sysfs
> +	  and debugfs)

Module name if "M" is chosen?


> +static char *accel_devnode(struct device *dev, umode_t *mode)
> +{
> +	return kasprintf(GFP_KERNEL, "accel/%s", dev_name(dev));
> +}
> +
> +static CLASS_ATTR_STRING(accel_version, 0444, "accel 1.0.0 20221018");

What is a version number doing here?

Please no, I understand that DRM has this, but it really does not make
sense for any in-kernel code.  And that's not how sysfs is supposed to
work anyway (if a file is present, the value is documented, if the file
is not present, the value is just not there, userspace has to handle
it all.)

> +
> +/**
> + * accel_sysfs_init - initialize sysfs helpers
> + *
> + * This is used to create the ACCEL class, which is the implicit parent of any
> + * other top-level ACCEL sysfs objects.
> + *
> + * You must call accel_sysfs_destroy() to release the allocated resources.
> + *
> + * Return: 0 on success, negative error code on failure.
> + */
> +static int accel_sysfs_init(void)
> +{
> +	int err;
> +
> +	accel_class = class_create(THIS_MODULE, "accel");
> +	if (IS_ERR(accel_class))
> +		return PTR_ERR(accel_class);
> +
> +	err = class_create_file(accel_class, &class_attr_accel_version.attr);

Hint, if you ever find yourself adding sysfs files "by hand" like this,
you are doing something wrong.  The driver code should create them
automatically for you by setting up default groups, _OR_ as in this
case, you shouldn't be adding the file at all :)

> +static void accel_sysfs_destroy(void)
> +{
> +	if (IS_ERR_OR_NULL(accel_class))
> +		return;
> +	class_remove_file(accel_class, &class_attr_accel_version.attr);

No need to manually destroy files when you remove a device.  But you
will remove this file anyway for the next version of this patch, so it's
not a big deal :)

> +	class_destroy(accel_class);
> +	accel_class = NULL;
> +}
> +
> +static int accel_stub_open(struct inode *inode, struct file *filp)
> +{
> +	DRM_DEBUG("Operation not supported");

ftrace is wonderful, please use that and not hand-rolled custom "I am
here!" type messages like this.

thanks,

greg k-h