Re: [PATCH v6 2/2] drm/xe: Align all VRAM scanout buffers to 64k physical pages when needed.

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

Hey,

Den 2024-08-26 kl. 21:30, skrev Matthew Brost:
> On Mon, Aug 26, 2024 at 07:01:16PM +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.
>>
>> The scanout flag and size being a multiple of 64k are used together
>> to enforce 64k physical placement.
>>
>> VM_BIND is completely unaffected, mappings to a VM can still be aligned
>> to 4k, just like for normal buffers.
>>
>> Signed-off-by: Zbigniew Kempczyński <zbigniew.kempczynski@intel.com>
>> Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.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 |  9 +++++++++
>>  drivers/gpu/drm/xe/xe_bo.c               |  7 +++++++
>>  drivers/gpu/drm/xe/xe_vm.c               | 11 ++++++++++-
>>  3 files changed, 26 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..63ce97cc4cfef 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 +29,14 @@ int intel_fb_bo_framebuffer_init(struct intel_framebuffer *intel_fb,
>>  	struct xe_device *xe = to_xe_device(bo->ttm.base.dev);
>>  	int ret;
>>  
>> +	/*
>> +	 * Some modifiers require physical alignment of 64KiB VRAM pages;
>> +	 * require that the BO in those cases is created correctly.
>> +	 */
>> +	if (XE_IOCTL_DBG(xe, intel_fb_needs_64k_phys(mode_cmd->modifier[0]) &&
>> +			     !(bo->flags & XE_BO_FLAG_NEEDS_64K)))
>> +		return -EINVAL;
> 
> I don't think this is correct use of this macro as XE_BO_FLAG_NEEDS_64K
> is an internal flag we set and typically this macro is used to santize
> user input. An assert here or WARN would make more sense.
Ideally we'd use 'is bo created as scanout', but that flag can be set by fb_init too, so if the BO was used for normal 4-tiled before, then as CCS it would pass when it wouldn't be valid.

I could change it to bo_created_with_scanout_flag_on_64k_platform inline, but I doubt that's more readable. :)

Cheers,
~Maarten