Re: [PATCH v2 4/5] drm: Add and export function drm_gem_cma_sync_data

[Paul Cercueil]

Le jeu. 11 mars 2021 à 12:28, Christoph Hellwig <hch@xxxxxxxxxxxxx> a 
écrit :
> On Sun, Mar 07, 2021 at 08:28:34PM +0000, Paul Cercueil wrote:
> >  +	drm_atomic_for_each_plane_damage(&iter, &clip) {
> >  +		for (i = 0; i < finfo->num_planes; i++) {
> >  +			daddr = drm_fb_cma_get_gem_addr(state->fb, state, i);
> >  +
> >  +			/* Ignore x1/x2 values, invalidate complete lines */
> >  +			offset = clip.y1 * state->fb->pitches[i];
> >  +
> >  +			dma_sync_single_for_device(dev, daddr + offset,
> >  +				       (clip.y2 - clip.y1) * state->fb->pitches[i],
> >  +				       DMA_TO_DEVICE);
>
> Are these helpers only ever used to transfer data to the device and
> never from it?  If so please clearly document that.

Yes. In the DRM world, are there cases where we transfer data from the 
device? I assume these cases are handled by v4l2 instead.

-Paul