drm/xe/vf: Track writes to inaccessible registers from VF

Only limited set of registers is accessible for the VF driver and
the hardware will silently drop writes to inaccessible registers.
To improve our VF driver lets intercept all such writes to warn
about such unexpected writes on debug builds or optionally allow
to provide some substitution (as a potential future extension).

Signed-off-by: Michal Wajdeczko <michal.wajdeczko@intel.com>
Cc: Gustavo Sousa <gustavo.sousa@intel.com>
Cc: Piotr Piórkowski <piotr.piorkowski@intel.com>
Reviewed-by: Piotr Piórkowski <piotr.piorkowski@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240713142643.1242-2-michal.wajdeczko@intel.com

drivers/gpu/drm/xe/xe_gt_sriov_vf.c

@@ -892,6 +892,32 @@ u32 xe_gt_sriov_vf_read32(struct xe_gt *gt, struct xe_reg reg)
 	return rr->value;
 }
 
+/**
+ * xe_gt_sriov_vf_write32 - Handle a write to an inaccessible register.
+ * @gt: the &xe_gt
+ * @reg: the register to write
+ * @val: value to write
+ *
+ * This function is for VF use only.
+ * Currently it will trigger a WARN if running on debug build.
+ */
+void xe_gt_sriov_vf_write32(struct xe_gt *gt, struct xe_reg reg, u32 val)
+{
+	u32 addr = xe_mmio_adjusted_addr(gt, reg.addr);
+
+	xe_gt_assert(gt, IS_SRIOV_VF(gt_to_xe(gt)));
+	xe_gt_assert(gt, !reg.vf);
+
+	/*
+	 * In the future, we may want to handle selected writes to inaccessible
+	 * registers in some custom way, but for now let's just log a warning
+	 * about such attempt, as likely we might be doing something wrong.
+	 */
+	xe_gt_WARN(gt, IS_ENABLED(CONFIG_DRM_XE_DEBUG),
+		   "VF is trying to write %#x to an inaccessible register %#x+%#x\n",
+		   val, reg.addr, addr - reg.addr);
+}
+
 /**
  * xe_gt_sriov_vf_print_config - Print VF self config.
  * @gt: the &xe_gt

drivers/gpu/drm/xe/xe_gt_sriov_vf.h

@@ -22,6 +22,7 @@ u32 xe_gt_sriov_vf_gmdid(struct xe_gt *gt);
 u16 xe_gt_sriov_vf_guc_ids(struct xe_gt *gt);
 u64 xe_gt_sriov_vf_lmem(struct xe_gt *gt);
 u32 xe_gt_sriov_vf_read32(struct xe_gt *gt, struct xe_reg reg);
+void xe_gt_sriov_vf_write32(struct xe_gt *gt, struct xe_reg reg, u32 val);
 
 void xe_gt_sriov_vf_print_config(struct xe_gt *gt, struct drm_printer *p);
 void xe_gt_sriov_vf_print_runtime(struct xe_gt *gt, struct drm_printer *p);

drivers/gpu/drm/xe/xe_mmio.c

@@ -171,7 +171,11 @@ void xe_mmio_write32(struct xe_gt *gt, struct xe_reg reg, u32 val)
 	u32 addr = xe_mmio_adjusted_addr(gt, reg.addr);
 
 	trace_xe_reg_rw(gt, true, addr, val, sizeof(val));
-	writel(val, (reg.ext ? tile->mmio_ext.regs : tile->mmio.regs) + addr);
+
+	if (!reg.vf && IS_SRIOV_VF(gt_to_xe(gt)))
+		xe_gt_sriov_vf_write32(gt, reg, val);
+	else
+		writel(val, (reg.ext ? tile->mmio_ext.regs : tile->mmio.regs) + addr);
 }
 
 u32 xe_mmio_read32(struct xe_gt *gt, struct xe_reg reg)