[PATCH v2 23/25] drm/xe/device: implement transient flush

[Balasubramani Vivekanandan]

From: Nirmoy Das <nirmoy.das at intel.com>

Display surfaces can be tagged as transient by mapping it using one of
the various L3:XD PAT index modes on Xe2. The expectation is that KMD
needs to request transient data flush at the start of flip sequence to
ensure all transient data in L3 cache is flushed to memory. Add a
routine for this which we can then call from the display code.

Signed-off-by: Nirmoy Das <nirmoy.das at intel.com>
Co-developed-by: Matthew Auld <matthew.auld at intel.com>
Signed-off-by: Matthew Auld <matthew.auld at intel.com>
Signed-off-by: Balasubramani Vivekanandan <balasubramani.vivekanandan at intel.com>
---
 drivers/gpu/drm/xe/regs/xe_gt_regs.h |  3 ++
 drivers/gpu/drm/xe/xe_device.c       | 52 ++++++++++++++++++++++++++++
 drivers/gpu/drm/xe/xe_device.h       |  2 ++
 3 files changed, 57 insertions(+)

diff --git a/drivers/gpu/drm/xe/regs/xe_gt_regs.h b/drivers/gpu/drm/xe/regs/xe_gt_regs.h
index 6617c86a096b..7afe810b3441 100644
--- a/drivers/gpu/drm/xe/regs/xe_gt_regs.h
+++ b/drivers/gpu/drm/xe/regs/xe_gt_regs.h
@@ -306,6 +306,9 @@
 
 #define XE2LPM_L3SQCREG5			XE_REG_MCR(0xb658)
 
+#define XE2_TDF_CTRL				XE_REG(0xb418)
+#define   TRANSIENT_FLUSH_REQUEST		REG_BIT(0)
+
 #define XEHP_MERT_MOD_CTRL			XE_REG_MCR(0xcf28)
 #define RENDER_MOD_CTRL				XE_REG_MCR(0xcf2c)
 #define COMP_MOD_CTRL				XE_REG_MCR(0xcf30)
diff --git a/drivers/gpu/drm/xe/xe_device.c b/drivers/gpu/drm/xe/xe_device.c
index 01bd5ccf05ca..0c9769fe04f6 100644
--- a/drivers/gpu/drm/xe/xe_device.c
+++ b/drivers/gpu/drm/xe/xe_device.c
@@ -641,6 +641,58 @@ void xe_device_wmb(struct xe_device *xe)
 		xe_mmio_write32(gt, SOFTWARE_FLAGS_SPR33, 0);
 }
 
+/**
+ * xe_device_td_flush() - Flush transient L3 cache entries
+ * @xe: The device
+ *
+ * Display engine has direct access to memory and is never coherent with L3/L4
+ * caches (or CPU caches), however KMD is responsible for specifically flushing
+ * transient L3 GPU cache entries prior to the flip sequence to ensure scanout
+ * can happen from such a surface without seeing corruption.
+ *
+ * Display surfaces can be tagged as transient by mapping it using one of the
+ * various L3:XD PAT index modes on Xe2.
+ *
+ * Note: On non-discrete xe2 platforms, like LNL, the entire L3 cache is flushed
+ * at the end of each submission via PIPE_CONTROL for compute/render, since SA
+ * Media is not coherent with L3 and we want to support render-vs-media
+ * usescases. For other engines like copy/blt the HW internally forces uncached
+ * behaviour, hence why we can skip the TDF on such platforms.
+ */
+void xe_device_td_flush(struct xe_device *xe)
+{
+	struct xe_gt *gt;
+	int err;
+	u8 id;
+
+	if (!IS_DGFX(xe) || GRAPHICS_VER(xe) < 20)
+		return;
+
+	for_each_gt(gt, xe, id) {
+		if (xe_gt_is_media_type(gt))
+			continue;
+
+		err = xe_force_wake_get(gt_to_fw(gt), XE_FW_GT);
+		if (err)
+			return;
+
+		xe_mmio_write32(gt, XE2_TDF_CTRL, TRANSIENT_FLUSH_REQUEST);
+		/*
+		 * FIXME: We can likely do better here with our choice of
+		 * timeout.  Currently we just assume the worst case, but really
+		 * we should make this dependent on how much actual L3 there is
+		 * for this system. Recomendation is to allow ~64us in the worst
+		 * case for 8M of L3 (assumes all entries are transient and need
+		 * to be flushed).
+		 */
+		if (xe_mmio_wait32(gt, XE2_TDF_CTRL, TRANSIENT_FLUSH_REQUEST, 0,
+				   150, NULL, false))
+			xe_gt_err_once(gt, "TD flush timeout\n");
+
+		xe_force_wake_put(gt_to_fw(gt), XE_FW_GT);
+	}
+}
+
 u32 xe_device_ccs_bytes(struct xe_device *xe, u64 size)
 {
 	return xe_device_has_flat_ccs(xe) ?
diff --git a/drivers/gpu/drm/xe/xe_device.h b/drivers/gpu/drm/xe/xe_device.h
index d413bc2c6be5..d3430f4b820a 100644
--- a/drivers/gpu/drm/xe/xe_device.h
+++ b/drivers/gpu/drm/xe/xe_device.h
@@ -176,4 +176,6 @@ void xe_device_snapshot_print(struct xe_device *xe, struct drm_printer *p);
 u64 xe_device_canonicalize_addr(struct xe_device *xe, u64 address);
 u64 xe_device_uncanonicalize_addr(struct xe_device *xe, u64 address);
 
+void xe_device_td_flush(struct xe_device *xe);
+
 #endif
-- 
2.25.1