[PATCH 3/5] drm/virtio: Return an error from connector dpms callback

[Daniel Vetter]

On Wed, Jul 26, 2017 at 10:56:34PM +0200, Takashi Iwai wrote:
> The virtio drm driver doesn't treat with DPMS, so we should return an
> error from the connector dpms callback so that the fbcon can fall back
> to the generic blank mode.
> 
> Signed-off-by: Takashi Iwai <tiwai at suse.de>
> ---
>  drivers/gpu/drm/virtio/virtgpu_display.c | 9 ++++++++-
>  1 file changed, 8 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/virtio/virtgpu_display.c b/drivers/gpu/drm/virtio/virtgpu_display.c
> index d51bd4521f17..77d5bad49c5f 100644
> --- a/drivers/gpu/drm/virtio/virtgpu_display.c
> +++ b/drivers/gpu/drm/virtio/virtgpu_display.c
> @@ -249,8 +249,15 @@ static void virtio_gpu_conn_destroy(struct drm_connector *connector)
>  	kfree(virtio_gpu_output);
>  }
>  
> +static int virtio_gpu_conn_dpms(struct drm_connector *connector, int mode)
> +{
> +	drm_atomic_helper_connector_dpms(connector, mode);
> +	/* FIXME: return error to make fbcon generic blank working */

Why FIXME here? You just fixed that issue, feels like should just be a
normal comment. I'd just say

	/* no DPMS for virtual drivers, it would close the window, making
	 * the guest inaccesible */

> +	return -EINVAL;

Ok, I've changed my plans for properties and DPMS a bit for atomic
drivers, and the ->dpms hook will be gone really soon. There's also the
problem that rejecting DPMS through the legacy interface, but allowing it
through the atomic interface isn't good api (and yes we have igts to check
for that).

I think it'd be better to reject this properly in the atomic_check phase
in the crtc_helper_funcs->atomic_check function, with something like this:

	if (crtc->state->enable && !crtc->state->active)
		return -EINVAL;

That should result in an -EINVAL for any caller who tries to update the
DPMS property. Which is important, since with the new atomic fbdev helper
code, fbdev does directly call into the atomic code and entirely bypasses
the ->dpms hook (that part is merged already, and why you need to rebase
patch 1).

That would also make sure that we don't return -EINVAL and still shut down
the screen (atomic does that for you, there's no difference between DPMS
off and fully disabling it).

Sorry that I'm dragging you all over with this for yet another respin :-/

Thanks, Daniel

> +}
> +
>  static const struct drm_connector_funcs virtio_gpu_connector_funcs = {
> -	.dpms = drm_atomic_helper_connector_dpms,
> +	.dpms = virtio_gpu_conn_dpms,
>  	.detect = virtio_gpu_conn_detect,
>  	.fill_modes = drm_helper_probe_single_connector_modes,
>  	.destroy = virtio_gpu_conn_destroy,
> -- 
> 2.13.3
> 
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-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch