Re: [PATCH v2 1/3] drm/xe: Align all 64k VRAM buffers physically when multiple of 64k.

[Maarten Lankhorst <maarten.lankhorst@linux.intel.com>]

Hey,

Den 2024-08-22 kl. 14:14, skrev Zbigniew Kempczyński:
> On Wed, Aug 21, 2024 at 10:56:35PM +0200, Maarten Lankhorst wrote:
>> For CCS formats on affected platforms, CCS can be used freely, but
>> display engine requires a multiple of 64k physical pages. No other
>> changes are needed.
>>
>> At the BO creation time we don't know if the BO will be used for CCS
>> or not. If the scanout flag is set, and the BO is a multiple of 64k,
>> we take the safe route and force the physical alignment of 64k pages.
>>
>> If the BO is not a multiple of 64k, or the scanout flag was not set
>> at BO creation, we reject it for usage as CCS in display. The physical
>> pages are likely not aligned correctly, and this will cause corruption
>> when used as FB.
>>
>> This is a slightly different approach from my previous patch. Instead
>> of requiring a scanout flag at FB creation, we now make all buffers of
>> the right size physically aligned correctly, so no change from userspace
>> is needed.
>>
>> It will be interesting to see if it affects performance in any way,
>> could potentially even improve things with 64k PTE's.
>>
>> Inspired by Zbigniews patch.
>>
>> Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
>> Co-developed-by: Zbigniew Kempczyński <zbigniew.kempczynski@intel.com>
>> Cc: Matthew Auld <matthew.auld@intel.com>
>> Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
>> Cc: Thomas Hellström <thomas.hellstrom@linux.intel.com>
>> Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
>> Cc: Juha-Pekka Heikkilä <juha-pekka.heikkila@intel.com>
>> ---
>>  drivers/gpu/drm/xe/display/intel_fb_bo.c |  6 ++++++
>>  drivers/gpu/drm/xe/xe_bo.c               | 10 ++++++++++
>>  drivers/gpu/drm/xe/xe_device_types.h     |  1 +
>>  drivers/gpu/drm/xe/xe_vm.c               |  3 ++-
>>  4 files changed, 19 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/gpu/drm/xe/display/intel_fb_bo.c b/drivers/gpu/drm/xe/display/intel_fb_bo.c
>> index f835492f73fb4..407367719abe2 100644
>> --- a/drivers/gpu/drm/xe/display/intel_fb_bo.c
>> +++ b/drivers/gpu/drm/xe/display/intel_fb_bo.c
>> @@ -7,6 +7,7 @@
>>  #include <drm/ttm/ttm_bo.h>
>>  
>>  #include "intel_display_types.h"
>> +#include "intel_fb.h"
>>  #include "intel_fb_bo.h"
>>  #include "xe_bo.h"
>>  
>> @@ -28,6 +29,11 @@ int intel_fb_bo_framebuffer_init(struct intel_framebuffer *intel_fb,
>>  	struct xe_device *xe = to_xe_device(bo->ttm.base.dev);
>>  	int ret;
>>  
>> +	if (XE_IOCTL_DBG(xe, intel_fb_is_ccs_modifier(mode_cmd->modifier[0]) &&
>> +			     (xe->info.vram_flags & XE_VRAM_FLAGS_DISPLAY_NEED64K_CCS) &&
>> +			     !(bo->flags & XE_BO_FLAG_NEEDS_64K)))
>> +		return -EINVAL;
>> +
>>  	xe_bo_get(bo);
>>  
>>  	ret = ttm_bo_reserve(&bo->ttm, true, false, NULL);
>> diff --git a/drivers/gpu/drm/xe/xe_bo.c b/drivers/gpu/drm/xe/xe_bo.c
>> index 6ed0e19552159..3a753f4644cb6 100644
>> --- a/drivers/gpu/drm/xe/xe_bo.c
>> +++ b/drivers/gpu/drm/xe/xe_bo.c
>> @@ -2017,6 +2017,16 @@ int xe_gem_create_ioctl(struct drm_device *dev, void *data,
>>  	if (args->flags & DRM_XE_GEM_CREATE_FLAG_SCANOUT)
>>  		bo_flags |= XE_BO_FLAG_SCANOUT;
> 
> I wonder, may you fail early here if buffer comes with SCANOUT flag but
> is not aligned to 64K when vram_flags has DISPLAY_NEED64K_CCS set and
> not wait to framebuffer init?
> 
I decided to allow this case. Because only a single format is affected (4-tiled CCS), it makes sense to allow scanout for all buffers and only fail on fb init.

Cheers,
~Maarten