Re: [PATCH 2/2] drm: Return -ENOTSUPP when called for KMS cap with a non-KMS driver

[Alex Deucher <alexdeucher@gmail.com>]

On Wed, Nov 30, 2016 at 4:07 AM, Daniel Vetter <daniel@ffwll.ch> wrote:
> On Wed, Nov 30, 2016 at 05:30:02PM +0900, Michel Dänzer wrote:
>> From: Michel Dänzer <michel.daenzer@amd.com>
>>
>> This is an attempt to make the previous fix a bit more robust going
>> forward.
>>
>> Signed-off-by: Michel Dänzer <michel.daenzer@amd.com>
>> ---
>>  drivers/gpu/drm/drm_ioctl.c | 23 +++++++++++++++++------
>>  1 file changed, 17 insertions(+), 6 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/drm_ioctl.c b/drivers/gpu/drm/drm_ioctl.c
>> index 71c3473..32f484b 100644
>> --- a/drivers/gpu/drm/drm_ioctl.c
>> +++ b/drivers/gpu/drm/drm_ioctl.c
>> @@ -229,6 +229,19 @@ static int drm_getcap(struct drm_device *dev, void *data, struct drm_file *file_
>>       struct drm_crtc *crtc;
>>
>>       req->value = 0;
>> +
>> +     /* Only allow non-KMS caps with non-KMS drivers */
>> +     switch (req->capability) {
>> +     case DRM_CAP_DUMB_BUFFER:
>
> Dumb buffers are only meant to be used for kms drivers, should be
> disallowed too.
>
>> +     case DRM_CAP_VBLANK_HIGH_CRTC:
>
> Might be good to have a comment here that we need to allow this for old
> ums?
>

I don't think we need this for UMS.  It was added for evergreen and we
only supported this feature on KMS.

Alex

>> +     case DRM_CAP_PRIME:
>> +     case DRM_CAP_TIMESTAMP_MONOTONIC:
>
> This is pretty new, I don't think any of the old ums drivers was ever
> updated to use it. Should probably disallow it too.
>> +             break;
>> +     default:
>> +             if (!drm_core_check_feature(dev, DRIVER_MODESET))
>> +                     return -ENOTSUPP;
>> +     }
>
> And one code org bikeshed: I don't like the duplicated switch, could we
> instead split it it into two disjoint sets like this?
>
>         switch (req->capability) {
>         case DRM_CAP_PRIME:
>                 req->value |= dev->driver->prime_fd_to_handle ? DRM_PRIME_CAP_IMPORT : 0;
>                 req->value |= dev->driver->prime_handle_to_fd ? DRM_PRIME_CAP_EXPORT : 0;
>                 break;
>         ... all other non-modeset caps ...
>         }
>
>         if (!drm_core_check_feature(dev, DRIVER_MODESET))
>                 return -ENOTSUPP;
>
>         switch (req->capability) {
>         ... handle remaining caps needed for DRIVER_MODSET ...
>         default:
>                 return -EINVAL;
>         }
>
> That way it would be a bit more obvious that people who add a new cap need
> to make a decision where to put it (and by default put it in the bottom
> pile).
> -Daniel
>
>>       switch (req->capability) {
>>       case DRM_CAP_DUMB_BUFFER:
>>               if (dev->driver->dumb_create)
>> @@ -254,12 +267,10 @@ static int drm_getcap(struct drm_device *dev, void *data, struct drm_file *file_
>>               req->value = dev->mode_config.async_page_flip;
>>               break;
>>       case DRM_CAP_PAGE_FLIP_TARGET:
>> -             if (drm_core_check_feature(dev, DRIVER_MODESET)) {
>> -                     req->value = 1;
>> -                     drm_for_each_crtc(crtc, dev) {
>> -                             if (!crtc->funcs->page_flip_target)
>> -                                     req->value = 0;
>> -                     }
>> +             req->value = 1;
>> +             drm_for_each_crtc(crtc, dev) {
>> +                     if (!crtc->funcs->page_flip_target)
>> +                             req->value = 0;
>>               }
>>               break;
>>       case DRM_CAP_CURSOR_WIDTH:
>> --
>> 2.10.2
>>
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>> dri-devel@lists.freedesktop.org
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>
> --
> Daniel Vetter
> Software Engineer, Intel Corporation
> http://blog.ffwll.ch
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> dri-devel@lists.freedesktop.org
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