[PATCH v4 04/11] drm/xe: Make it possible to read instance0 MCR registers after xe_gt_mcr_init_early

[Lucas De Marchi]

On Thu, Jun 19, 2025 at 12:49:03PM +0200, Maarten Lankhorst wrote:
>After mcr_init_early, we need to be able to do VRAM and CCS probing
>without hwconfig probe. Fortunately the relevant registers are all
>instance 0, which fortunately means no dependencies on further initialization
>is required.
>
>Reviewed-by: Matt Roper <matthew.d.roper at intel.com>
>[mlankhorst: Fix british spelling]

^ not sure what you mean here, but should probably be gone from commit
message.


>Signed-off-by: Maarten Lankhorst <dev at lankhorst.se>



Reviewed-by: Lucas De Marchi <lucas.demarchi at intel.com>

Lucas De Marchi

>---
> drivers/gpu/drm/xe/xe_gt_mcr.c   | 47 ++++++++++++++++++--------------
> drivers/gpu/drm/xe/xe_gt_types.h |  2 ++
> 2 files changed, 29 insertions(+), 20 deletions(-)
>
>diff --git a/drivers/gpu/drm/xe/xe_gt_mcr.c b/drivers/gpu/drm/xe/xe_gt_mcr.c
>index d4d9730f0d2c7..64a2f0d6aaf95 100644
>--- a/drivers/gpu/drm/xe/xe_gt_mcr.c
>+++ b/drivers/gpu/drm/xe/xe_gt_mcr.c
>@@ -420,12 +420,6 @@ static void init_steering_sqidi_psmi(struct xe_gt *gt)
> 	gt->steering[SQIDI_PSMI].instance_target = select & 0x1;
> }
>
>-static void init_steering_inst0(struct xe_gt *gt)
>-{
>-	gt->steering[INSTANCE0].group_target = 0;	/* unused */
>-	gt->steering[INSTANCE0].instance_target = 0;	/* unused */
>-}
>-
> static const struct {
> 	const char *name;
> 	void (*init)(struct xe_gt *gt);
>@@ -436,7 +430,7 @@ static const struct {
> 	[DSS] =		{ "DSS",	init_steering_dss },
> 	[OADDRM] =	{ "OADDRM / GPMXMT", init_steering_oaddrm },
> 	[SQIDI_PSMI] =  { "SQIDI_PSMI", init_steering_sqidi_psmi },
>-	[INSTANCE0] =	{ "INSTANCE 0",	init_steering_inst0 },
>+	[INSTANCE0] =	{ "INSTANCE 0",	NULL },
> 	[IMPLICIT_STEERING] = { "IMPLICIT", NULL },
> };
>
>@@ -446,25 +440,17 @@ static const struct {
>  *
>  * Perform early software only initialization of the MCR lock to allow
>  * the synchronization on accessing the STEER_SEMAPHORE register and
>- * use the xe_gt_mcr_multicast_write() function.
>+ * use the xe_gt_mcr_multicast_write() function, plus the minimum
>+ * safe MCR registers required for VRAM/CCS probing.
>  */
> void xe_gt_mcr_init_early(struct xe_gt *gt)
> {
>+	struct xe_device *xe = gt_to_xe(gt);
>+
> 	BUILD_BUG_ON(IMPLICIT_STEERING + 1 != NUM_STEERING_TYPES);
> 	BUILD_BUG_ON(ARRAY_SIZE(xe_steering_types) != NUM_STEERING_TYPES);
>
> 	spin_lock_init(&gt->mcr_lock);
>-}
>-
>-/**
>- * xe_gt_mcr_init - Normal initialization of the MCR support
>- * @gt: GT structure
>- *
>- * Perform normal initialization of the MCR for all usages.
>- */
>-void xe_gt_mcr_init(struct xe_gt *gt)
>-{
>-	struct xe_device *xe = gt_to_xe(gt);
>
> 	if (IS_SRIOV_VF(xe))
> 		return;
>@@ -505,10 +491,27 @@ void xe_gt_mcr_init(struct xe_gt *gt)
> 		}
> 	}
>
>+	/* Mark instance 0 as initialized, we need this early for VRAM and CCS probe. */
>+	gt->steering[INSTANCE0].initialized = true;
>+}
>+
>+/**
>+ * xe_gt_mcr_init - Normal initialization of the MCR support
>+ * @gt: GT structure
>+ *
>+ * Perform normal initialization of the MCR for all usages.
>+ */
>+void xe_gt_mcr_init(struct xe_gt *gt)
>+{
>+	if (IS_SRIOV_VF(gt_to_xe(gt)))
>+		return;
>+
> 	/* Select non-terminated steering target for each type */
>-	for (int i = 0; i < NUM_STEERING_TYPES; i++)
>+	for (int i = 0; i < NUM_STEERING_TYPES; i++) {
>+		gt->steering[i].initialized = true;
> 		if (gt->steering[i].ranges && xe_steering_types[i].init)
> 			xe_steering_types[i].init(gt);
>+	}
> }
>
> /**
>@@ -570,6 +573,10 @@ bool xe_gt_mcr_get_nonterminated_steering(struct xe_gt *gt,
>
> 		for (int i = 0; gt->steering[type].ranges[i].end > 0; i++) {
> 			if (xe_mmio_in_range(&gt->mmio, &gt->steering[type].ranges[i], reg)) {
>+				drm_WARN(&gt_to_xe(gt)->drm, !gt->steering[type].initialized,
>+					 "Uninitialized usage of MCR register %s/%#x\n",
>+					 xe_steering_types[type].name, reg.addr);
>+
> 				*group = gt->steering[type].group_target;
> 				*instance = gt->steering[type].instance_target;
> 				return true;
>diff --git a/drivers/gpu/drm/xe/xe_gt_types.h b/drivers/gpu/drm/xe/xe_gt_types.h
>index 7def0959da35d..96344c6047260 100644
>--- a/drivers/gpu/drm/xe/xe_gt_types.h
>+++ b/drivers/gpu/drm/xe/xe_gt_types.h
>@@ -377,6 +377,8 @@ struct xe_gt {
> 		u16 group_target;
> 		/** @steering.instance_target: instance to steer accesses to */
> 		u16 instance_target;
>+		/** @steering.initialized: Whether this steering range is initialized */
>+		bool initialized;
> 	} steering[NUM_STEERING_TYPES];
>
> 	/**
>-- 
>2.45.2
>