Re: [PATCH] drm/sun4i: layers: Use drm_fb_dma_get_gem_addr() to get display memory

[Chen-Yu Tsai]

Hi,

On Tue, Mar 10, 2026 at 12:56 AM Chen-Yu Tsai <wens@xxxxxxxxxx> wrote:
>
> Commit 4636ce93d5b2 ("drm/fb-cma-helper: Add drm_fb_cma_get_gem_addr()")
> adds a new helper, which covers fetching a drm_framebuffer's GEM object
> and calculating the buffer address for a given plane.
>
> This patch uses this helper to replace our own open coded version of the
> same function.
>
> Signed-off-by: Chen-Yu Tsai <wens@xxxxxxxxxx>
> ---
>  drivers/gpu/drm/sun4i/sun8i_ui_layer.c | 16 ++-------------
>  drivers/gpu/drm/sun4i/sun8i_vi_layer.c | 27 ++------------------------
>  2 files changed, 4 insertions(+), 39 deletions(-)
>
> diff --git a/drivers/gpu/drm/sun4i/sun8i_ui_layer.c b/drivers/gpu/drm/sun4i/sun8i_ui_layer.c
> index f08f6da55dd0..72c92203ae63 100644
> --- a/drivers/gpu/drm/sun4i/sun8i_ui_layer.c
> +++ b/drivers/gpu/drm/sun4i/sun8i_ui_layer.c
> @@ -124,25 +124,13 @@ static void sun8i_ui_layer_update_buffer(struct sun8i_layer *layer,
>  {
>         struct drm_plane_state *state = plane->state;
>         struct drm_framebuffer *fb = state->fb;
> -       struct drm_gem_dma_object *gem;
>         dma_addr_t dma_addr;
>         u32 ch_base;
> -       int bpp;
>
>         ch_base = sun8i_channel_base(layer);
>
> -       /* Get the physical address of the buffer in memory */
> -       gem = drm_fb_dma_get_gem_obj(fb, 0);
> -
> -       DRM_DEBUG_DRIVER("Using GEM @ %pad\n", &gem->dma_addr);
> -
> -       /* Compute the start of the displayed memory */
> -       bpp = fb->format->cpp[0];
> -       dma_addr = gem->dma_addr + fb->offsets[0];
> -
> -       /* Fixup framebuffer address for src coordinates */
> -       dma_addr += (state->src.x1 >> 16) * bpp;
> -       dma_addr += (state->src.y1 >> 16) * fb->pitches[0];
> +       /* Get the start of the displayed memory */
> +       dma_addr = drm_fb_dma_get_gem_addr(fb, state, 0);

I just realized while reading more code that there's a subtle difference
here.

The original code used state->src.x1, which is the "clipped" coordinates,
while drm_fb_dma_get_gem_addr() uses state->src_x, which is the original
coordinates.

Jernej, do you know which one the driver is supposed to use? Or maybe
it doesn't matter?


ChenYu