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

[Icenowy Zheng]

在 2026-09-17四的 19:42 +0800，Chen-Yu Tsai写道：
> On Thu, Sep 17, 2026 at 7:16 PM Icenowy Zheng <uwu@xxxxxxxxxx> wrote:
> > 
> > 在 2026-09-16三的 11:33 +0800，Chen-Yu Tsai写道：
> > > 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()

Yes, it seems so. I checked newest rc, but this change is in drm-misc-
next. Sorry for the noise.

> 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.

Yes it looks like thedrm_fb_dma_get_gem_addr() helper already handled
the non-clipping source offset.

Thanks,
Icenowy

> 
> 
> ChenYu
> 
> > Thanks,
> > Icenowy
> > 
> > > 
> > > 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(-)