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

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Message-ID: <CAFCwf13uLj=P6u6FAcY8M5qAXoaBdb+Ha-TYj0j2FAZnFAPFYg@mail.gmail.com>
Date:   Thu, 3 Nov 2022 15:31:45 +0200
From:   Oded Gabbay <ogabbay@...nel.org>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     David Airlie <airlied@...il.com>, Daniel Vetter <daniel@...ll.ch>,
        Arnd Bergmann <arnd@...db.de>, linux-kernel@...r.kernel.org,
        dri-devel@...ts.freedesktop.org, Jason Gunthorpe <jgg@...dia.com>,
        John Hubbard <jhubbard@...dia.com>,
        Alex Deucher <alexander.deucher@....com>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Maxime Ripard <mripard@...nel.org>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        Yuji Ishikawa <yuji2.ishikawa@...hiba.co.jp>,
        Jiho Chu <jiho.chu@...sung.com>,
        Daniel Stone <daniel@...ishbar.org>,
        Tvrtko Ursulin <tvrtko.ursulin@...ux.intel.com>,
        Jeffrey Hugo <quic_jhugo@...cinc.com>,
        Christoph Hellwig <hch@...radead.org>,
        Kevin Hilman <khilman@...libre.com>,
        Jagan Teki <jagan@...rulasolutions.com>,
        Jacek Lawrynowicz <jacek.lawrynowicz@...ux.intel.com>,
        Maciej Kwapulinski <maciej.kwapulinski@...ux.intel.com>
Subject: Re: [RFC PATCH v2 1/3] drivers/accel: define kconfig and register a
 new major

On Thu, Nov 3, 2022 at 2:31 AM Greg Kroah-Hartman
<gregkh@...uxfoundation.org> wrote:
>
> 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?
Will add
>
>
> > +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.)
Actually I don't know if drm even uses that. I just copied it to be
identical to drm's sysfs, but
as accel doesn't have any history, I can remove it.
>
> > +
> > +/**
> > + * 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 :)
ok, removed.

>
> > +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.
I'll just remove it as this line is being replaced anyway in the next patch.
Thanks,
Oded
>
> thanks,
>
> greg k-h