[RFC PATCH 3/3] drm: add dedicated minor for accelerator devices

[Oded Gabbay]

On Tue, Oct 25, 2022 at 9:43 AM Jiho Chu <jiho.chu at samsung.com> wrote:
>
>
> On Sun, 23 Oct 2022 00:46:22 +0300
> Oded Gabbay <ogabbay at kernel.org> wrote:
>
> > diff --git a/drivers/gpu/drm/drm_drv.c b/drivers/gpu/drm/drm_drv.c
> > index b58ffb1433d6..c13701a8d4be 100644
> > --- a/drivers/gpu/drm/drm_drv.c
> > +++ b/drivers/gpu/drm/drm_drv.c
> > @@ -56,6 +56,9 @@ MODULE_LICENSE("GPL and additional rights");
> >  static DEFINE_SPINLOCK(drm_minor_lock);
> >  static struct idr drm_minors_idr;
> >
> > +static DEFINE_SPINLOCK(accel_minor_lock);
> > +static struct idr accel_minors_idr;
> > +
> >  /*
> >   * If the drm core fails to init for whatever reason,
> >   * we should prevent any drivers from registering with it.
> > @@ -94,6 +97,8 @@ static struct drm_minor **drm_minor_get_slot(struct drm_device *dev,
> >               return &dev->primary;
> >       case DRM_MINOR_RENDER:
> >               return &dev->render;
> > +     case DRM_MINOR_ACCEL:
> > +             return &dev->accel;
> >       default:
> >               BUG();
> >       }
> > @@ -108,9 +113,15 @@ static void drm_minor_alloc_release(struct drm_device *dev, void *data)
> >
> >       put_device(minor->kdev);
> >
> > -     spin_lock_irqsave(&drm_minor_lock, flags);
> > -     idr_remove(&drm_minors_idr, minor->index);
> > -     spin_unlock_irqrestore(&drm_minor_lock, flags);
> > +     if (minor->type == DRM_MINOR_ACCEL) {
> > +             spin_lock_irqsave(&accel_minor_lock, flags);
> > +             idr_remove(&accel_minors_idr, minor->index);
> > +             spin_unlock_irqrestore(&accel_minor_lock, flags);
> > +     } else {
> > +             spin_lock_irqsave(&drm_minor_lock, flags);
> > +             idr_remove(&drm_minors_idr, minor->index);
> > +             spin_unlock_irqrestore(&drm_minor_lock, flags);
> > +     }
> >  }
> >
> >  static int drm_minor_alloc(struct drm_device *dev, unsigned int type)
> > @@ -127,13 +138,23 @@ static int drm_minor_alloc(struct drm_device *dev, unsigned int type)
> >       minor->dev = dev;
> >
> >       idr_preload(GFP_KERNEL);
> > -     spin_lock_irqsave(&drm_minor_lock, flags);
> > -     r = idr_alloc(&drm_minors_idr,
> > -                   NULL,
> > -                   64 * type,
> > -                   64 * (type + 1),
> > -                   GFP_NOWAIT);
> > -     spin_unlock_irqrestore(&drm_minor_lock, flags);
> > +     if (type == DRM_MINOR_ACCEL) {
> > +             spin_lock_irqsave(&accel_minor_lock, flags);
> > +             r = idr_alloc(&accel_minors_idr,
> > +                     NULL,
> > +                     64 * (type - DRM_MINOR_ACCEL),
> > +                     64 * (type - DRM_MINOR_ACCEL + 1),
> > +                     GFP_NOWAIT);
> > +             spin_unlock_irqrestore(&accel_minor_lock, flags);
> > +     } else {
> > +             spin_lock_irqsave(&drm_minor_lock, flags);
> > +             r = idr_alloc(&drm_minors_idr,
> > +                     NULL,
> > +                     64 * type,
> > +                     64 * (type + 1),
> > +                     GFP_NOWAIT);
> > +             spin_unlock_irqrestore(&drm_minor_lock, flags);
> > +     }
>
> Hi,
> There are many functions which checks drm type and decides its behaviors. It's good to
> re-use exiting codes, but accel devices use totally different major/minor, and so it needs to be moved to
> /drvier/accel/ (maybe later..). How about seperating functions for alloc/release minor (accel_minor_alloc..)?
> also, for others which have drm type related codes.
My feeling was moving the minor code handling to a different file (in
addition to moving the major code handling) will cause too much
duplication.
My main theme is that an accel minor is another minor in drm, even if
a bit different. i.e. It uses the same drm_minor structure.
The driver declares he wants to use this minor using a drm driver feature flag.
imo, all of that indicates the code should be inside drm.
>
>
>
>
> > @@ -607,6 +652,14 @@ static int drm_dev_init(struct drm_device *dev,
> >       /* no per-device feature limits by default */
> >       dev->driver_features = ~0u;
> >
> > +     if (drm_core_check_feature(dev, DRIVER_COMPUTE_ACCEL) &&
> > +                             (drm_core_check_feature(dev, DRIVER_RENDER) ||
> > +                             drm_core_check_feature(dev, DRIVER_MODESET))) {
> > +
> > +             DRM_ERROR("DRM driver can't be both a compute acceleration and graphics driver\n");
> > +             return -EINVAL;
> > +     }
> > +
>
> It's fine for the device only for acceleration, but can't graphic devices have acceleration feature?
Of course they can :) In that case, and if they want to expose an
accel device char, they should write an accel driver and connect it to
their main graphics driver via auxiliary bus.

I could have added two flags - compute_accel, and compute_accel_only
(similar to a patch that was sent to add render only flag), but imo it
would make the code more convoluted. I prefer the clean separation and
using standard auxiliary bus.

Thanks,
Oded

>
>
> Thanks,
> Jiho Chu