Friendly ping on this series - v3 addressed the review feedback from v1/v2 (added the missing st7735r driver). Happy to rebase and resend if anything's changed on drm-misc-next since September, or if there's any other feedback.
On Wed, Sep 23, 2026 at 3:58 PM Jonathan Frazin <[email protected]> wrote: > > A drm/tiny MIPI DBI panel can currently only scan out a framebuffer that is > exactly panel-sized, always from the origin. This series lets a client > allocate a larger framebuffer and choose the displayed region via the plane > source rectangle - a crop / pan with no scaling. > > Motivation: feeding hardware-decoded video to a small SPI panel. The video > decoder emits a fixed frame size; being able to point the panel at a > panel-sized window of that buffer avoids a full-frame CPU copy on every flush > and lets userspace pan/centre the image. > > Patch 1 is the actual fix - mipi_dbi_fb_dirty() addressed the controller in > framebuffer coordinates, which is only correct while src_x/src_y are zero. It > now subtracts the plane source origin. > > Patch 2 raises mode_config.max_width/height (pinned to the panel size) on the > six drm/tiny drivers that flush through the shared > drm_mipi_dbi_plane_helper_atomic_update(). ili9225 is excluded - it has its > own flush path that does not carry the source offset. > > Open question for patch 2: the six drivers each set the limits identically in > their probe. This could instead be a shared helper (or folded into > drm_mipi_dbi_dev_init / the DRM_MIPI_DBI_MODE_CONFIG_* macros) so future > drivers get it for free. Happy to respin that way if preferred - the > per-driver form is what is shown here because it is the smaller diff and > easier to review a first pass. > > The min_width/min_height, the fixed mode, the connector and the mode-sized > transfer buffer are all unchanged, and > drm_mipi_dbi_plane_helper_atomic_check() still enforces DRM_PLANE_NO_SCALING > and no repositioning, so the flushed rectangle stays bounded by the panel > regardless of the framebuffer dimensions. > > Tested on hardware: ILI9341 and ST7789V (through panel-mipi-dbi), both > 240x320 - an oversized framebuffer is accepted and a non-zero-offset > panel-sized window scans out correctly; a panel-sized framebuffer is > unchanged. HX8357D was tested during the downstream review by Dave Stevenson > (Cc'd). ili9486, mi0283qt, ili9163 and st7735r are build-tested only. > > Both patches have been carried in the Raspberry Pi kernel (rpi-7.2.y) and in > use there: https://github.com/raspberrypi/linux/pull/7589. The v1/v2 > heap-overflow fix (see below) has also been folded back into that downstream > kernel: https://github.com/raspberrypi/linux/pull/7643. > > Applies to current mainline / drm-misc-next; the touched files are identical > there. > > Changes since v2: > - Patch 1: a damage clip that lies entirely within the one-pixel sliver > the v2 clamp cuts off collapses the clamped rectangle to zero width or > height. That was still being passed to mipi_dbi_set_window_address(), > producing an inverted (start past end) address window ahead of a > zero-length write - undefined behaviour per the MIPI DCS spec. Skip > the flush when the clamped rectangle is empty. > - Patch 2: st7735r also flushes through the shared > drm_mipi_dbi_plane_helper_atomic_update() but was missed from the > original list - it lives under drivers/gpu/drm/sitronix/ rather than > drivers/gpu/drm/tiny/. Added it, and confirmed by grepping the whole > tree for DRM_MIPI_DBI_PLANE_HELPER_FUNCS that no other driver shares > this path. Thanks again to the automated review for catching both of > these on v2. > > Changes since v1: > - Patch 1: clamp the damage rectangle to the panel's fixed mode before > using it, instead of trusting it to already be panel-sized. src_x/src_y > are the plane source origin truncated to whole pixels, but the > rectangle from drm_atomic_helper_damage_merged() is clipped against > that origin's exact 16.16 fixed-point value - when the origin has a > fractional part, the rectangle's far edge could land up to a pixel past > where the truncated origin would place the panel's own width/height, > overflowing the panel-sized tx_buf. Thanks to the automated review for > catching this. > - Patch 2: unchanged. > > Jonathan Frazin (2): > drm/mipi-dbi: honour the plane source offset when flushing > drm/tiny: allow a framebuffer larger than the panel on MIPI DBI > drivers > > drivers/gpu/drm/drm_mipi_dbi.c | 43 +++++++++++++++++++++++---- > drivers/gpu/drm/sitronix/st7735r.c | 8 +++-- > drivers/gpu/drm/tiny/hx8357d.c | 8 +++-- > drivers/gpu/drm/tiny/ili9163.c | 8 +++-- > drivers/gpu/drm/tiny/ili9341.c | 8 +++-- > drivers/gpu/drm/tiny/ili9486.c | 8 +++-- > drivers/gpu/drm/tiny/mi0283qt.c | 8 +++-- > drivers/gpu/drm/tiny/panel-mipi-dbi.c | 8 +++-- > 8 files changed, 80 insertions(+), 19 deletions(-) > > -- > 2.53.0
