Hi

Am 11.03.21 um 13:33 schrieb Paul Cercueil:

Le jeu. 11 mars 2021 à 12:28, Christoph Hellwig [off-list ref] a 
écrit :

quoted

On Sun, Mar 07, 2021 at 08:28:34PM +0000, Paul Cercueil wrote:

quoted

 +    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.

Software rendering (i.e., anything wrt dumb buffers) likely reads back 
framebuffer content during blit operations. For devices where this is a 
slow operation (e.g., PCI read) we set struct 
drm_mode_config.prefer_shadow to hint renderers to use shadow buffering.

Best regards
Thomas

-Paul

-- 
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Maxfeldstr. 5, 90409 Nürnberg, Germany
(HRB 36809, AG Nürnberg)
Geschäftsführer: Felix Imendörffer