Hi Paul,having individual functions for each mode only makes sense if the decision is at compile time. But in patch 5, you're working around your earlier design by introducing in-driver helpers that select the correct CMA function.
In SHMEM helpers we have the flag map_wc in the GEM structure that selects the pages caching mode (wc vs uncached). I think CMA should use this design as well. Have a map_noncoherent flag in the CMA GEM object and set it from the driver's implementation of gem_create_object.
And in the long run, we could try to consolidate all drivers/helpers mapping flags in struct drm_gem_object.
Best regards Thomas Am 07.03.21 um 21:28 schrieb Paul Cercueil:
Rework of my previous patchset which added support for GEM buffers backed by non-coherent memory to the ingenic-drm driver. Having GEM buffers backed by non-coherent memory is interesting in the particular case where it is faster to render to a non-coherent buffer then sync the data cache, than to render to a write-combine buffer, and (by extension) much faster than using a shadow buffer. This is true for instance on some Ingenic SoCs, where even simple blits (e.g. memcpy) are about three times faster using this method. For the record, the previous patchset was accepted for 5.10 then had to be reverted, as it conflicted with some changes made to the DMA API. This new patchset is pretty different as it adds the functionality to the DRM core. The first three patches add variants to existing functions but with the "non-coherent memory" twist, exported as GPL symbols. The fourth patch adds a function to be used with the damage helpers. Finally, the last patch adds support for non-coherent GEM buffers to the ingenic-drm driver. The functionality is enabled through a module parameter, and is disabled by default. Cheers, -Paul Paul Cercueil (5): drm: Add and export function drm_gem_cma_create_noncoherent drm: Add and export function drm_gem_cma_dumb_create_noncoherent drm: Add and export function drm_gem_cma_mmap_noncoherent drm: Add and export function drm_gem_cma_sync_data drm/ingenic: Add option to alloc cached GEM buffers drivers/gpu/drm/drm_gem_cma_helper.c | 223 +++++++++++++++++++--- drivers/gpu/drm/ingenic/ingenic-drm-drv.c | 49 ++++- drivers/gpu/drm/ingenic/ingenic-drm.h | 4 + drivers/gpu/drm/ingenic/ingenic-ipu.c | 14 +- include/drm/drm_gem_cma_helper.h | 13 ++ 5 files changed, 273 insertions(+), 30 deletions(-)
-- Thomas Zimmermann Graphics Driver Developer SUSE Software Solutions Germany GmbH Maxfeldstr. 5, 90409 Nürnberg, Germany (HRB 36809, AG Nürnberg) Geschäftsführer: Felix Imendörffer
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