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

[Daniel Vetter]

On Wed, Nov 30, 2016 at 05:30:02PM +0900, Michel Dänzer wrote:
> From: Michel Dänzer <michel.daenzer at amd.com>
> 
> This is an attempt to make the previous fix a bit more robust going
> forward.
> 
> Signed-off-by: Michel Dänzer <michel.daenzer at 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?

> +	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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-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch