Re: [PATCH RFT v2 0/5] drm: Add and use drm_fb_dma_get_gem_clipped_addr() helper

On Thu, Sep 17, 2026 at 7:16 PM Icenowy Zheng [off-list ref] wrote:

在 2026-09-16三的 11:33 +0800，Chen-Yu Tsai写道：

quoted

Hi,

This is v2 of my drm_fb_dma_get_gem_clipped_addr() series.

Changes since v1:
- Add and use new drm_framebuffer_get_block_offset() helper (Thomas)


This series adds a helper to retrieve the buffer starting address of
a
"clipped" framebuffer. This contrasts with drm_fb_dma_get_gem_addr(),
which gives the address of the full buffer.

Should vs_fb_get_dma_addr() in verisilicon/vs_plane.c be replaced with
this helper too?

I implemented manual framebuffer offset addition here.

Didn't I replace vs_fb_get_dma_addr() with drm_fb_dma_get_gem_addr()
already? At the time only primary and cursor planes were supported by
the driver. The primary plane can't be clipped, and the cursor plane
had some custom clipping, but seemed to want the unclipped address.


ChenYu

Thanks,
Icenowy

quoted

Some drivers program their hardware with clipped dimensions, so they
should be using the clipped buffer address as well, unless the
hardware
can advance the scanout directly. (Side note: many drivers still use
the non-clipped dimensions.)

While at it, also pull out the offset calculation of
drm_fb_dma_get_gem_addr()
into a separate helper in drm_framebuffer.[ch], thereby separating
responsibilities.

The sun4i driver was recently incorrectly converted to use the
unclipped
drm_fb_dma_get_gem_addr() helper. This broke offsets into subsampled
pixel groups, but also exposed the mismatch between the dimensions
used
vs the buffer address. Two other drivers were also touched.


Patch 1 adds a new helper to return the byte offset into a
framebuffer
for the start of the pixel block of the given pixel coordinates.

Patch 2 adds the new helper to return the buffer address based on
clipped coordinates.

Patch 3 switches the sun4i driver to the new helper, and fixes the
luma plane buffer address offset for subsampled YUV formats.

Patch 4 converts the imx/dc driver to use the new helper. This fixes
a
mismatch between the programmed coordinates and the buffer address.

Patch 5 replaces the open coded buffer address calculation in the
imx/dcss driver with the new helper. Existing behavior, which might
be
wrong, is preserved.


Please help test. The series is only compile tested on my end. The
sun4i
changes should revert its behavior to before the
drm_fb_dma_get_gem_addr()
was adopted. The imx/dcss changes should not have any behavioral
difference.


Thanks
ChenYu

Chen-Yu Tsai (5):
  drm: Split framebuffer pixel offset calculation from
    drm_fb_dma_get_gem_addr()
  drm/fb-dma-helper: Add drm_fb_dma_get_gem_clipped_addr()
  drm/sun4i: layers: Fix VI buffer address for clipped offsets
  drm/imx/dc: plane: Switch to drm_fb_dma_get_gem_clipped_addr()
  drm/imx/dcss: plane: Switch to drm_fb_dma_get_gem_clipped_addr()

 drivers/gpu/drm/drm_fb_dma_helper.c    | 61 ++++++++++++++----------
--
 drivers/gpu/drm/drm_framebuffer.c      | 45 +++++++++++++++++++
 drivers/gpu/drm/imx/dc/dc-plane.c      |  4 +-
 drivers/gpu/drm/imx/dcss/dcss-plane.c  | 34 ++++++--------
 drivers/gpu/drm/sun4i/sun8i_ui_layer.c |  2 +-
 drivers/gpu/drm/sun4i/sun8i_vi_layer.c | 16 ++++++-
 include/drm/drm_fb_dma_helper.h        |  4 ++
 include/drm/drm_framebuffer.h          |  3 ++
 8 files changed, 118 insertions(+), 51 deletions(-)