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

[Michal Wajdeczko]

Only limited set of registers is accessible for the VF driver.
The hardware will silently drop writes to inaccessible registers,
but to improve our driver lets track all such unexpected writes
on debug builds.

We will explicitly ignore writes to SOFTWARE_FLAGS_SPR33 since it
is used by the driver just to mimic wmb and we do not have any
similar unused scratch register accessible from the VF.

Signed-off-by: Michal Wajdeczko <michal.wajdeczko at intel.com>
---
 drivers/gpu/drm/xe/xe_gt_sriov_vf.c | 22 ++++++++++++++++++++++
 drivers/gpu/drm/xe/xe_gt_sriov_vf.h |  1 +
 drivers/gpu/drm/xe/xe_mmio.c        |  6 +++++-
 3 files changed, 28 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/xe/xe_gt_sriov_vf.c b/drivers/gpu/drm/xe/xe_gt_sriov_vf.c
index 41e46a00c01e..36cefe3161e1 100644
--- a/drivers/gpu/drm/xe/xe_gt_sriov_vf.c
+++ b/drivers/gpu/drm/xe/xe_gt_sriov_vf.c
@@ -892,6 +892,28 @@ u32 xe_gt_sriov_vf_read32(struct xe_gt *gt, struct xe_reg reg)
 	return rr->value;
 }
 
+/**
+ * xe_gt_sriov_vf_write32 - Track writes to an inaccessible registers.
+ * @gt: the &xe_gt
+ * @reg: the register to write
+ * @val: value to write
+ *
+ * This function is for VF use only.
+ * This function is dedicated for registers that VFs can't write directly.
+ * 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);
+
+	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
diff --git a/drivers/gpu/drm/xe/xe_gt_sriov_vf.h b/drivers/gpu/drm/xe/xe_gt_sriov_vf.h
index 0de7f8cbcfa6..e541ce57bec2 100644
--- a/drivers/gpu/drm/xe/xe_gt_sriov_vf.h
+++ b/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);
diff --git a/drivers/gpu/drm/xe/xe_mmio.c b/drivers/gpu/drm/xe/xe_mmio.c
index f92faad4b96d..ff72afd79272 100644
--- a/drivers/gpu/drm/xe/xe_mmio.c
+++ b/drivers/gpu/drm/xe/xe_mmio.c
@@ -151,7 +151,11 @@ 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)) && reg.addr != SOFTWARE_FLAGS_SPR33.addr)
+		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)
-- 
2.43.0