linux-kernel - Re: [RFC PATCH 2/3] drm: define new accel major and register it

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Date:   Mon, 24 Oct 2022 17:52:10 +1000
From:   Dave Airlie <airlied@...il.com>
To:     Oded Gabbay <ogabbay@...nel.org>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        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 2/3] drm: define new accel major and register it

On Mon, 24 Oct 2022 at 17:23, Oded Gabbay <ogabbay@...nel.org> wrote:
>
> On Sun, Oct 23, 2022 at 3:40 PM Greg Kroah-Hartman
> <gregkh@...uxfoundation.org> wrote:
> >
> > On Sun, Oct 23, 2022 at 12:46:21AM +0300, Oded Gabbay wrote:
> > > The accelerator devices will be exposed to the user space with a new,
> > > dedicated major number - 261.
> > >
> > > The drm core registers the new major number as a char device and create
> > > corresponding sysfs and debugfs root entries, same as for the drm major.
> > >
> > > In case CONFIG_ACCEL is not selected, this code is not compiled in.
> > >
> > > Signed-off-by: Oded Gabbay <ogabbay@...nel.org>
> > > ---
> > >  Documentation/admin-guide/devices.txt |  5 +++
> > >  drivers/gpu/drm/drm_drv.c             | 45 +++++++++++++++++++++++
> > >  drivers/gpu/drm/drm_internal.h        |  3 ++
> > >  drivers/gpu/drm/drm_sysfs.c           | 52 +++++++++++++++++++++++++++
> > >  include/drm/drm_ioctl.h               |  1 +
> > >  5 files changed, 106 insertions(+)
> > >
> > > diff --git a/Documentation/admin-guide/devices.txt b/Documentation/admin-guide/devices.txt
> > > index 9764d6edb189..06c525e01ea5 100644
> > > --- a/Documentation/admin-guide/devices.txt
> > > +++ b/Documentation/admin-guide/devices.txt
> > > @@ -3080,6 +3080,11 @@
> > >                 ...
> > >                 255 = /dev/osd255     256th OSD Device
> > >
> > > + 261 char    Compute Acceleration Devices
> > > +               0 = /dev/accel/accel0 First acceleration device
> > > +               1 = /dev/accel/accel1 Second acceleration device
> > > +                 ...
> > > +
> > >   384-511 char        RESERVED FOR DYNAMIC ASSIGNMENT
> > >               Character devices that request a dynamic allocation of major
> > >               number will take numbers starting from 511 and downward,
> > > diff --git a/drivers/gpu/drm/drm_drv.c b/drivers/gpu/drm/drm_drv.c
> > > index 8214a0b1ab7f..b58ffb1433d6 100644
> > > --- a/drivers/gpu/drm/drm_drv.c
> > > +++ b/drivers/gpu/drm/drm_drv.c
> > > @@ -67,6 +67,10 @@ static bool drm_core_init_complete;
> > >
> > >  static struct dentry *drm_debugfs_root;
> > >
> > > +#ifdef CONFIG_ACCEL
> > > +static struct dentry *accel_debugfs_root;
> > > +#endif
> > > +
> > >  DEFINE_STATIC_SRCU(drm_unplug_srcu);
> > >
> > >  /*
> > > @@ -1031,9 +1035,19 @@ static const struct file_operations drm_stub_fops = {
> > >       .llseek = noop_llseek,
> > >  };
> > >
> > > +static void accel_core_exit(void)
> > > +{
> > > +#ifdef CONFIG_ACCEL
> > > +     unregister_chrdev(ACCEL_MAJOR, "accel");
> > > +     debugfs_remove(accel_debugfs_root);
> > > +     accel_sysfs_destroy();
> > > +#endif
> > > +}
> >
> > Why is all of this in drm_drv.c?
> >
> > Why not put it in drm/accel/accel.c or something like that?  Then put
> > the proper stuff into a .h file and then you have no #ifdef in the .c
> > files.
> I thought about that, adding an accel.c in drivers/accel/ and putting
> this code there.
> Eventually I thought that for two functions it's not worth it, but I
> guess that in addition to the reason you gave, one can argue that
> there will probably be more code in that file anyway, so why not open
> it now.
> I'll change this if no one else thinks otherwise.

Seems like a good idea to start doing it now, might make things easier
to keep separated.

Dave.