Re: [PATCH v3 7/7] drm/xe/uapi: Add a query flag for has_device_atomics_on_smem

[Lionel Landwerlin <lionel.g.landwerlin@intel.com>]

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On 15/04/2024 17:52, Nirmoy Das wrote:
> Add a query flag for xe->info.has_device_atomics_on_smem
> as this is platform dependent. This flag can be use to inform
> whether DRM_XE_VM_BIND_FLAG_DEVICE_ATOMICS can be effectively
> applied for a given platform.
>
> Signed-off-by: Nirmoy Das<nirmoy.das@intel.com>
> ---
>   drivers/gpu/drm/xe/xe_query.c | 3 +++
>   include/uapi/drm/xe_drm.h     | 5 ++++-
>   2 files changed, 7 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/xe/xe_query.c b/drivers/gpu/drm/xe/xe_query.c
> index df407d73e5f5..43272fdd5442 100644
> --- a/drivers/gpu/drm/xe/xe_query.c
> +++ b/drivers/gpu/drm/xe/xe_query.c
> @@ -336,6 +336,9 @@ static int query_config(struct xe_device *xe, struct drm_xe_device_query *query)
>   	if (xe_device_get_root_tile(xe)->mem.vram.usable_size)
>   		config->info[DRM_XE_QUERY_CONFIG_FLAGS] =
>   			DRM_XE_QUERY_CONFIG_FLAG_HAS_VRAM;
> +	if (xe->info.has_device_atomics_on_smem)
> +		config->info[DRM_XE_QUERY_CONFIG_FLAGS] |=
> +			DRM_XE_QUERY_CONFIG_FLAG_HAS_DEV_ATOMIC_ON_SMEM;
>   	config->info[DRM_XE_QUERY_CONFIG_MIN_ALIGNMENT] =
>   		xe->info.vram_flags & XE_VRAM_FLAGS_NEED64K ? SZ_64K : SZ_4K;
>   	config->info[DRM_XE_QUERY_CONFIG_VA_BITS] = xe->info.va_bits;
> diff --git a/include/uapi/drm/xe_drm.h b/include/uapi/drm/xe_drm.h
> index ca4447e10ac9..80fff6fe3199 100644
> --- a/include/uapi/drm/xe_drm.h
> +++ b/include/uapi/drm/xe_drm.h
> @@ -389,6 +389,8 @@ struct drm_xe_query_mem_regions {
>    *
>    *    - %DRM_XE_QUERY_CONFIG_FLAG_HAS_VRAM - Flag is set if the device
>    *      has usable VRAM
> + *    - %DRM_XE_QUERY_CONFIG_FLAG_HAS_DEV_ATOMIC_ON_SMEM - Flag is set if the device
> + *      supports device atomics on system memory
>    *  - %DRM_XE_QUERY_CONFIG_MIN_ALIGNMENT - Minimal memory alignment
>    *    required by this device, typically SZ_4K or SZ_64K
>    *  - %DRM_XE_QUERY_CONFIG_VA_BITS - Maximum bits of a virtual address
> @@ -404,7 +406,8 @@ struct drm_xe_query_config {
>   
>   #define DRM_XE_QUERY_CONFIG_REV_AND_DEVICE_ID	0
>   #define DRM_XE_QUERY_CONFIG_FLAGS			1
> -	#define DRM_XE_QUERY_CONFIG_FLAG_HAS_VRAM	(1 << 0)
> +	#define DRM_XE_QUERY_CONFIG_FLAG_HAS_VRAM		(1 << 0)
> +	#define DRM_XE_QUERY_CONFIG_FLAG_HAS_DEV_ATOMIC_ON_SMEM	(1 << 1)


I find this flag a bit confusing, because it would imply that platforms 
that do not report this flag don't suppoort atomics on smem.

But for DG2/MTL/TGL (if officially supported by Xe), that's not the 
case, yet they do support this.


Maybe renaming this 
toDRM_XE_QUERY_CONFIG_FLAG_HAS_EXPLICIT_DEV_ATOMIC_ON_SMEM would make 
more sense.

Meaning the platform requires a specific vm_bind flag to get atomics 
working on SMEM only BO.

-Lionel


>   #define DRM_XE_QUERY_CONFIG_MIN_ALIGNMENT		2
>   #define DRM_XE_QUERY_CONFIG_VA_BITS			3
>   #define DRM_XE_QUERY_CONFIG_MAX_EXEC_QUEUE_PRIORITY	4


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