Re: [PATCH v6 16/30] drm/xe/vf: Use GUC_HXG_TYPE_EVENT for GuC context register

["Lis, Tomasz" <tomasz.lis@intel.com>]

On 10/6/2025 1:10 PM, Matthew Brost wrote:
> The only case where the GuC submission backend cannot reason 100%
> correctly is when a GuC context is registered during VF post-migration
> recovery. In this scenario, it's possible that the GuC context register
> H2G is processed, but the immediately following schedule-enable H2G gets
> lost.
>
> A double register is harmless when using `GUC_HXG_TYPE_EVENT`, as GuC
> simply drops the duplicate H2G. To keep things simple, use
> `GUC_HXG_TYPE_EVENT` for all context registrations on VFs.
>
> v5:
>   - Check for xe_sriov_vf_migration_supported (Tomasz)
>
> Signed-off-by: Matthew Brost <matthew.brost@intel.com>
> ---
>   drivers/gpu/drm/xe/xe_guc_ct.c | 33 +++++++++++++++++++++++++--------
>   1 file changed, 25 insertions(+), 8 deletions(-)
>
> diff --git a/drivers/gpu/drm/xe/xe_guc_ct.c b/drivers/gpu/drm/xe/xe_guc_ct.c
> index 9f0090ae64a6..3ac654cebc79 100644
> --- a/drivers/gpu/drm/xe/xe_guc_ct.c
> +++ b/drivers/gpu/drm/xe/xe_guc_ct.c
> @@ -32,6 +32,7 @@
>   #include "xe_guc_tlb_inval.h"
>   #include "xe_map.h"
>   #include "xe_pm.h"
> +#include "xe_sriov_vf.h"
>   #include "xe_trace_guc.h"
>   
>   static void receive_g2h(struct xe_guc_ct *ct);
> @@ -736,6 +737,26 @@ static u16 next_ct_seqno(struct xe_guc_ct *ct, bool is_g2h_fence)
>   	return seqno;
>   }
>   
> +#define MAKE_ACTION(type, __action)				\
> +({								\
> +	FIELD_PREP(GUC_HXG_MSG_0_TYPE, type) |			\
> +	FIELD_PREP(GUC_HXG_EVENT_MSG_0_ACTION |			\
> +		   GUC_HXG_EVENT_MSG_0_DATA0, __action);	\
> +})
> +
> +static bool vf_action_can_safely_fail(struct xe_device *xe, u32 action)
> +{
> +	/*
> +	 * If we are VF resuming, we can't exactly track if a context
> +	 * registration has been completed in the GuC state machine, it is
> +	 * harmless to resend as it will just fail silently if
> +	 * GUC_HXG_TYPE_EVENT is used.

Maybe add:

If the registration H2G fails with error other than ALREADY_REGISTERED, 
we will know due to the shortly following schedule-enable H2G failing.

Other than that, a second to Michal:

Reviewed-by: Tomasz Lis <tomasz.lis@intel.com>

> +	 */
> +	return IS_SRIOV_VF(xe) && xe_sriov_vf_migration_supported(xe) &&
> +		(action == XE_GUC_ACTION_REGISTER_CONTEXT_MULTI_LRC ||
> +		 action == XE_GUC_ACTION_REGISTER_CONTEXT);
> +}
> +
>   #define H2G_CT_HEADERS (GUC_CTB_HDR_LEN + 1) /* one DW CTB header and one DW HxG header */
>   
>   static int h2g_write(struct xe_guc_ct *ct, const u32 *action, u32 len,
> @@ -807,18 +828,14 @@ static int h2g_write(struct xe_guc_ct *ct, const u32 *action, u32 len,
>   		FIELD_PREP(GUC_CTB_MSG_0_NUM_DWORDS, len) |
>   		FIELD_PREP(GUC_CTB_MSG_0_FENCE, ct_fence_value);
>   	if (want_response) {
> -		cmd[1] =
> -			FIELD_PREP(GUC_HXG_MSG_0_TYPE, GUC_HXG_TYPE_REQUEST) |
> -			FIELD_PREP(GUC_HXG_EVENT_MSG_0_ACTION |
> -				   GUC_HXG_EVENT_MSG_0_DATA0, action[0]);
> +		cmd[1] = MAKE_ACTION(GUC_HXG_TYPE_REQUEST, action[0]);
> +	} else if (vf_action_can_safely_fail(xe, action[0])) {
> +		cmd[1] = MAKE_ACTION(GUC_HXG_TYPE_EVENT, action[0]);
>   	} else {
>   		fast_req_track(ct, ct_fence_value,
>   			       FIELD_GET(GUC_HXG_EVENT_MSG_0_ACTION, action[0]));
>   
> -		cmd[1] =
> -			FIELD_PREP(GUC_HXG_MSG_0_TYPE, GUC_HXG_TYPE_FAST_REQUEST) |
> -			FIELD_PREP(GUC_HXG_EVENT_MSG_0_ACTION |
> -				   GUC_HXG_EVENT_MSG_0_DATA0, action[0]);
> +		cmd[1] = MAKE_ACTION(GUC_HXG_TYPE_FAST_REQUEST, action[0]);
>   	}
>   
>   	/* H2G header in cmd[1] replaces action[0] so: */