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

[Jeffrey Hugo]

On 10/24/2022 1:52 AM, Dave Airlie wrote:
> On Mon, 24 Oct 2022 at 17:23, Oded Gabbay <ogabbay@xxxxxxxxxx> wrote:
> > On Sun, Oct 23, 2022 at 3:40 PM Greg Kroah-Hartman
> > <gregkh@xxxxxxxxxxxxxxxxxxx> 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@xxxxxxxxxx>
> > > > ---
> > > >   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.

I agree.  I was a bit confused going through this patch, and envisioning 
how an accel driver would use the interface.  I think an 
accel_internal.h would be clearer.

-Jeff