linux-kernel - Re: [PATCH v2 4/5] drm: Add and export function drm_gem_cma_sync

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Date:   Thu, 11 Mar 2021 12:28:46 +0000
From:   Christoph Hellwig <hch@...radead.org>
To:     Paul Cercueil <paul@...pouillou.net>
Cc:     Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Maxime Ripard <mripard@...nel.org>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Sam Ravnborg <sam@...nborg.org>, od@...c.me,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        linux-mips@...r.kernel.org
Subject: Re: [PATCH v2 4/5] drm: Add and export function drm_gem_cma_sync_data

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.