Re: [PATCH] drm/xe/pat: sanity check compression and coh_mode

[Nirmoy Das <nirmoy.das@linux.intel.com>]

On 8/28/2024 11:22 AM, Matthew Auld wrote:
> There is an implicit assumption in the driver that compression and
> coh_1way+ are mutually exclusive. If this is ever not true then userptr
> and imported dma-buf from external device will have uncleared ccs state.
> Add a build bug for this so we don't forget.
>
> Signed-off-by: Matthew Auld <matthew.auld@intel.com>
> Cc: Thomas Hellström <thomas.hellstrom@linux.intel.com>
> Cc: Nirmoy Das <nirmoy.das@intel.com>
Reviewed-by: Nirmoy Das <nirmoy.das@intel.com>
> ---
>   drivers/gpu/drm/xe/xe_pat.c | 7 ++++++-
>   1 file changed, 6 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/xe/xe_pat.c b/drivers/gpu/drm/xe/xe_pat.c
> index 722278cc23fc..f92a1c61956d 100644
> --- a/drivers/gpu/drm/xe/xe_pat.c
> +++ b/drivers/gpu/drm/xe/xe_pat.c
> @@ -100,6 +100,10 @@ static const struct xe_pat_table_entry xelpg_pat_table[] = {
>    * Reserved entries should be programmed with the maximum caching, minimum
>    * coherency (which matches an all-0's encoding), so we can just omit them
>    * in the table.
> + *
> + * Note: There is an implicit assumption in the driver that compression and
> + * coh_1way+ are mutually exclusive. If this is ever not true then userptr
> + * and imported dma-buf from external device will have uncleared ccs state.
>    */
>   #define XE2_PAT(no_promote, comp_en, l3clos, l3_policy, l4_policy, __coh_mode) \
>   	{ \
> @@ -109,7 +113,8 @@ static const struct xe_pat_table_entry xelpg_pat_table[] = {
>   			REG_FIELD_PREP(XE2_L3_POLICY, l3_policy) | \
>   			REG_FIELD_PREP(XE2_L4_POLICY, l4_policy) | \
>   			REG_FIELD_PREP(XE2_COH_MODE, __coh_mode), \
> -		.coh_mode = __coh_mode ? XE_COH_AT_LEAST_1WAY : XE_COH_NONE \
> +		.coh_mode = (BUILD_BUG_ON_ZERO(__coh_mode && comp_en) || __coh_mode) ? \
> +			XE_COH_AT_LEAST_1WAY : XE_COH_NONE \
>   	}
>   
>   static const struct xe_pat_table_entry xe2_pat_table[] = {