On 10/5/23 11:04, Thomas Zimmermann wrote: > DRM's format-conversion helpers require temporary memory. Pass the > buffer from the caller and keep it allocated over several calls. Allow > the caller to preallocate the buffer memory. > > The motivation for this patchset is the recent work on a DRM panic > handler. [1] The panic handler requires format conversion to display an > error to the screen. But allocating memory during kernel panics is > fragile. The changes in this patchset enable the DRM panic handler to > preallocate buffer storage before the panic occurs. > I've been thinking about this and afaiu this requires the display hw to switch to the new panic buffer for scanout, right? I don't think that is possible for any complex hw to do in a panic situation. Or are you thinking that the driver should somehow "memcpy" this buffer to the actual scanout buffer? Noralf. > As an additonal benefit, drivers can now keep the temporary storage > across multiple updates. Avoiding memory allocation slightly reduces > the CPU overhead of the format helpers. > > Patch 1 adds struct drm_format_conv_state, a simple interface to pass > around the buffer storage. Patch 2 adds an instance of the struct to > the shadow-plane state. Patch 3 moves the buffer's memory management > from the format helpers into their callers within the DRM drivers. Most > of the afected drivers use the state instance stored in their shadow- > plane state. The shadow-plane code releases the buffer memory automatically. > > Patches 4 to 7 update three drivers to preallocate the format-conversion > buffer in their plane's atomic_check function. The driver thus detects OOM > errors before the display update begins. > > Tested with simpledrm. > > v4: > * rename struct to drm_format_conv_state (Javier) > * replace ARRAY_SIZE() with sizeof() (Jani) > * store buffer in shadow-plane state (Javier, Maxime) > * prealloc in atomic_check in several drivers > v3: > * no changes > v2: > * reserve storage during probing in the drivers > > [1] https://patchwork.freedesktop.org/series/122244/ > > Thomas Zimmermann (7): > drm/format-helper: Cache buffers with struct drm_format_conv_state > drm/atomic-helper: Add format-conversion state to shadow-plane state > drm/format-helper: Pass format-conversion state to helpers > drm/ofdrm: Preallocate format-conversion buffer in atomic_check > drm/simpledrm: Preallocate format-conversion buffer in atomic_check > drm/ssd130x: Fix atomic_check for disabled planes > drm/ssd130x: Preallocate format-conversion buffer in atomic_check > > drivers/gpu/drm/drm_format_helper.c | 212 +++++++++++++----- > drivers/gpu/drm/drm_gem_atomic_helper.c | 9 + > drivers/gpu/drm/drm_mipi_dbi.c | 19 +- > drivers/gpu/drm/gud/gud_pipe.c | 30 ++- > drivers/gpu/drm/solomon/ssd130x.c | 36 ++- > .../gpu/drm/tests/drm_format_helper_test.c | 72 +++--- > drivers/gpu/drm/tiny/cirrus.c | 3 +- > drivers/gpu/drm/tiny/ili9225.c | 10 +- > drivers/gpu/drm/tiny/ofdrm.c | 16 +- > drivers/gpu/drm/tiny/repaper.c | 8 +- > drivers/gpu/drm/tiny/simpledrm.c | 43 +++- > drivers/gpu/drm/tiny/st7586.c | 19 +- > include/drm/drm_format_helper.h | 81 +++++-- > include/drm/drm_gem_atomic_helper.h | 10 + > include/drm/drm_mipi_dbi.h | 4 +- > 15 files changed, 428 insertions(+), 144 deletions(-) > > > base-commit: 57d3b83a83c5527325efb5bcaf594da09fe4a41b
