Am 07.02.22 um 14:53 schrieb Ramalingam C:
On 2022-02-07 at 12:41:59 +0100, Christian König wrote:
Am 07.02.22 um 10:37 schrieb Ramalingam C:
On flat-ccs capable platform we need to evict and resore the ccs data along with the corresponding main memory.
This ccs data can only be access through BLT engine through a special cmd ( )
To support above requirement of flat-ccs enabled i915 platforms this series adds new param called ccs_pages_needed to the ttm_tt_init(), to increase the ttm_tt->num_pages of system memory when the obj has the lmem placement possibility.
Well question is why isn't the buffer object allocated with the extra space in the first place?
Hi Christian,
On Xe-HP and later devices, we use dedicated compression control state (CCS) stored in local memory for each surface, to support the 3D and media compression formats.
The memory required for the CCS of the entire local memory is 1/256 of the local memory size. So before the kernel boot, the required memory is reserved for the CCS data and a secure register will be programmed with the CCS base address
So when we allocate a object in local memory we dont need to explicitly allocate the space for ccs data. But when we evict the obj into the smem to hold the compression related data along with the obj we need smem space of obj_size + (obj_size/256).
Hence when we create smem for an obj with lmem placement possibility we create with the extra space.
Exactly that's what I've been missing in the cover letter and/or commit messages, comments etc..
Over all sounds like a valid explanation to me, just one comment on the code/naming:
int ttm_tt_init(struct ttm_tt *ttm, struct ttm_buffer_object *bo,
uint32_t page_flags, enum ttm_caching caching)
uint32_t page_flags, enum ttm_caching caching,unsigned long ccs_pages)
Please don't try to leak any i915 specific stuff into common TTM code.
For example use the wording extra_pages instead of ccs_pages here.
Apart from that looks good to me, Christian.
Ram.
Regards, Christian.
This will be on top of the flat-ccs enabling series https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Fpatchwork....
For more about flat-ccs feature please have a look at https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Fpatchwork....
Testing of the series is WIP and looking forward for the early review on the amendment to ttm_tt_init and the approach.
Ramalingam C (2): drm/i915/ttm: Add extra pages for handling ccs data drm/i915/migrate: Evict and restore the ccs data
drivers/gpu/drm/drm_gem_vram_helper.c | 2 +- drivers/gpu/drm/i915/gem/i915_gem_ttm.c | 23 +- drivers/gpu/drm/i915/gt/intel_migrate.c | 283 +++++++++++---------- drivers/gpu/drm/qxl/qxl_ttm.c | 2 +- drivers/gpu/drm/ttm/ttm_agp_backend.c | 2 +- drivers/gpu/drm/ttm/ttm_tt.c | 12 +- drivers/gpu/drm/vmwgfx/vmwgfx_ttm_buffer.c | 2 +- include/drm/ttm/ttm_tt.h | 4 +- 8 files changed, 191 insertions(+), 139 deletions(-)