While porting i915 to arm64 we noticed some issues accessing lmem. Some writes were getting corrupted and the final state of the buffer didn't have exactly what we wrote. This became evident when enabling GuC submission: depending on the number of engines the ADS struct was being corrupted and GuC would reject it, refusin to initialize.
From Documentation/core-api/bus-virt-phys-mapping.rst:
This memory is called "PCI memory" or "shared memory" or "IO memory" or whatever, and there is only one way to access it: the readb/writeb and related functions. You should never take the address of such memory, because there is really nothing you can do with such an address: it's not conceptually in the same memory space as "real memory" at all, so you cannot just dereference a pointer. (Sadly, on x86 it **is** in the same memory space, so on x86 it actually works to just deference a pointer, but it's not portable).
When reading or writing words directly to IO memory, in order to be portable the Linux kernel provides the abstraction detailed in section "Differences between I/O access functions" of Documentation/driver-api/device-io.rst.
This limits our ability to simply overlay our structs on top a buffer and directly access it since that buffer may come from IO memory rather than system memory. Hence the approach taken in intel_guc_ads.c needs to be refactored. This is not the only place in i915 that neeed to be changed, but the one causing the most problems, with a real reproducer. This first set of patch focuses on fixing the gem object to pass the ADS
After the addition of a few helpers in the dma_buf_map API, most of intel_guc_ads.c can be converted to use it. The exception is the regset initialization: we'd incur into a lot of extra indirection when reading/writting each register. So the regset is converted to use a temporary buffer allocated on probe, which is then copied to its final location when finishing the initialization or on gt reset.
Testing on some discrete cards, after this change we can correctly pass the ADS struct to GuC and have it initialized correctly.
thanks Lucas De Marchi
Cc: linux-media@vger.kernel.org Cc: dri-devel@lists.freedesktop.org Cc: linaro-mm-sig@lists.linaro.org Cc: linux-kernel@vger.kernel.org Cc: Christian König christian.koenig@amd.com Cc: Daniel Vetter daniel@ffwll.ch Cc: Daniele Ceraolo Spurio daniele.ceraolospurio@intel.com Cc: David Airlie airlied@linux.ie Cc: John Harrison John.C.Harrison@Intel.com Cc: Joonas Lahtinen joonas.lahtinen@linux.intel.com Cc: Maarten Lankhorst maarten.lankhorst@linux.intel.com Cc: Matt Roper matthew.d.roper@intel.com Cc: Matthew Auld matthew.auld@intel.com Cc: Matthew Brost matthew.brost@intel.com Cc: Sumit Semwal sumit.semwal@linaro.org Cc: Thomas Hellström thomas.hellstrom@linux.intel.com Cc: Tvrtko Ursulin tvrtko.ursulin@linux.intel.com
Lucas De Marchi (19): dma-buf-map: Add read/write helpers dma-buf-map: Add helper to initialize second map drm/i915/gt: Add helper for shmem copy to dma_buf_map drm/i915/guc: Keep dma_buf_map of ads_blob around drm/i915/guc: Add read/write helpers for ADS blob drm/i915/guc: Convert golden context init to dma_buf_map drm/i915/guc: Convert policies update to dma_buf_map drm/i915/guc: Convert engine record to dma_buf_map dma-buf-map: Add wrapper over memset drm/i915/guc: Convert guc_ads_private_data_reset to dma_buf_map drm/i915/guc: Convert golden context prep to dma_buf_map drm/i915/guc: Replace check for golden context size drm/i915/guc: Convert mapping table to dma_buf_map drm/i915/guc: Convert capture list to dma_buf_map drm/i915/guc: Prepare for error propagation drm/i915/guc: Use a single pass to calculate regset drm/i915/guc: Convert guc_mmio_reg_state_init to dma_buf_map drm/i915/guc: Convert __guc_ads_init to dma_buf_map drm/i915/guc: Remove plain ads_blob pointer
drivers/gpu/drm/i915/gt/shmem_utils.c | 32 ++ drivers/gpu/drm/i915/gt/shmem_utils.h | 3 + drivers/gpu/drm/i915/gt/uc/intel_guc.h | 14 +- drivers/gpu/drm/i915/gt/uc/intel_guc_ads.c | 374 +++++++++++------- drivers/gpu/drm/i915/gt/uc/intel_guc_ads.h | 3 +- .../gpu/drm/i915/gt/uc/intel_guc_submission.c | 11 +- include/linux/dma-buf-map.h | 127 ++++++ 7 files changed, 405 insertions(+), 159 deletions(-)