On Adreno GPUs there is an option to shadow the RPTR register in GPU accessible memory. The shadow memory allows the kernel driver to query the value of the RPTR for each ringbuffer even if it is preempted out or if the GPU is turned off during aggressive power management.
There are risks to using the RPTR shadow. If it is in GPU accessible memory it could be read or written by any GPU operation. All versions of the GPU hardware except A650 requires the shadow to be in unprivileged memory which opens it to risk.
This series does two things. First, it marks as many buffers as possible as privileged. For a5xx these are some preemption buffers and on a650 this includes all global buffers (such as the ringbuffer and memstore). I've sent these patches before but they tie in well with this series so I've included them.
Then we disable the RPTR shadow across all targets. For all targets except for a5xx the RPTR shadow isn't needed so there isn't a loss of functionality. a5xx does need it for preemption so that has to be temporarily disabled.
Later changes will re-enable the shadow for those targets that can safely mitigate the risks.
Jordan Crouse (4): drm/msm: Split the a5xx preemption record drm/msm: Enable expanded apriv support for a650 drm/msm: Disable premption on all 5xx targets drm/msm: Disable the RPTR shadow
drivers/gpu/drm/msm/adreno/a2xx_gpu.c | 5 +++++ drivers/gpu/drm/msm/adreno/a3xx_gpu.c | 10 +++++++++ drivers/gpu/drm/msm/adreno/a4xx_gpu.c | 10 +++++++++ drivers/gpu/drm/msm/adreno/a5xx_gpu.c | 14 +++++++++--- drivers/gpu/drm/msm/adreno/a5xx_gpu.h | 1 + drivers/gpu/drm/msm/adreno/a5xx_preempt.c | 25 ++++++++++++++++----- drivers/gpu/drm/msm/adreno/a6xx_gpu.c | 13 ++++++++++- drivers/gpu/drm/msm/adreno/adreno_gpu.c | 27 ++--------------------- drivers/gpu/drm/msm/msm_gpu.c | 2 +- drivers/gpu/drm/msm/msm_gpu.h | 11 +++++++++ drivers/gpu/drm/msm/msm_ringbuffer.c | 4 ++-- 11 files changed, 85 insertions(+), 37 deletions(-)