This patchset adds a library for shmem backed GEM objects and makes use of it in tinydrm.
When I made tinydrm I used the CMA helper because it was very easy to use. July last year I learned that this limits which drivers to PRIME import from, since CMA requires continuous memory. tinydrm drivers don't require that. So I set out to change that looking first at shmem, but that wasn't working since shmem didn't work with fbdev deferred I/O. Then I did a vmalloc buffer attempt which worked with deferred I/O, but maybe wouldn't be of so much use as a library for other drivers to use. As my work to split out stuff from the CMA helper for shared use came to an end, I had a generic fbdev emulation that uses a shadow buffer for deferred I/O. This means that I can now use shmem buffers after all.
I have looked at the other drivers that use drm_gem_get_pages() and several supports different cache modes so I've done that even though tinydrm only uses the cached one.
tinydrm can both use vmalloc and shmem buffers, it doesn't matter as far as I can see. So the question is what will benefit the rest of DRM the most.
Note: Sparse has this complaint, but the problem is in kvmalloc_array(): include/linux/mm.h:592:13: error: undefined identifier '__builtin_mul_overflow'
Noralf.
Changes since version 1: - Fix missing argument in docs (kbuild test robot) - Fix: sparse: expression using sizeof(void) (kbuild test robot) - Rebasing gave a new checkpatch warning, so I changed to bitfields: CHECK: Avoid using bool structure members because of possible alignment issues - see: https://lkml.org/lkml/2017/11/21/384 #834: FILE: include/drm/drm_gem_shmem_helper.h:84: + bool pages_mark_dirty_on_put; #841: FILE: include/drm/drm_gem_shmem_helper.h:91: + bool pages_mark_accessed_on_put;
Noralf Trønnes (2): drm: Add library for shmem backed GEM objects drm/tinydrm: Switch from CMA to shmem buffers
Documentation/gpu/drm-kms-helpers.rst | 12 + drivers/gpu/drm/Kconfig | 6 + drivers/gpu/drm/Makefile | 1 + drivers/gpu/drm/drm_gem_shmem_helper.c | 676 +++++++++++++++++++++++++ drivers/gpu/drm/tinydrm/Kconfig | 2 +- drivers/gpu/drm/tinydrm/core/tinydrm-core.c | 91 +--- drivers/gpu/drm/tinydrm/core/tinydrm-helpers.c | 5 + drivers/gpu/drm/tinydrm/ili9225.c | 14 +- drivers/gpu/drm/tinydrm/ili9341.c | 6 +- drivers/gpu/drm/tinydrm/mi0283qt.c | 6 +- drivers/gpu/drm/tinydrm/mipi-dbi.c | 38 +- drivers/gpu/drm/tinydrm/repaper.c | 24 +- drivers/gpu/drm/tinydrm/st7586.c | 15 +- drivers/gpu/drm/tinydrm/st7735r.c | 6 +- include/drm/drm_gem_shmem_helper.h | 198 ++++++++ include/drm/tinydrm/tinydrm.h | 36 +- 16 files changed, 982 insertions(+), 154 deletions(-) create mode 100644 drivers/gpu/drm/drm_gem_shmem_helper.c create mode 100644 include/drm/drm_gem_shmem_helper.h