panfrost: Disable CRC at <16x16 tile sizes

The hardware writes one CRC per (effective) tile, the tile size of the CRC
buffer is the same as the configured effective tile size. However, all our CRC
infrastructure assumes 16x16 tiles. In case CRC is used with smaller tiles,
buffer overflows and incorrect rendering are all possible. Don't use CRC at
smaller tile sizes. Note disabling CRC correctly invalidates any bound CRC
buffers.

Fixes: 2e97d7c835 ("panfrost: Transaction elimination support")
Closes: #6332
Signed-off-by: Alyssa Rosenzweig <alyssa@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/16983>
(cherry picked from commit 44223e5f28)

.pick_status.json

@@ -166,7 +166,7 @@
         "description": "panfrost: Disable CRC at <16x16 tile sizes",
         "nominated": true,
         "nomination_type": 1,
-        "resolution": 0,
+        "resolution": 1,
         "main_sha": null,
         "because_sha": "2e97d7c8350385dbf962a1d6caa5acae667d1c95"
     },

src/panfrost/lib/pan_blitter.c

@@ -1046,7 +1046,10 @@ pan_preload_emit_pre_frame_dcd(struct pan_pool *desc_pool,
         void *dcd = fb->bifrost.pre_post.dcds.cpu +
                     (dcd_idx * pan_size(DRAW));
 
-        int crc_rt = GENX(pan_select_crc_rt)(fb);
+        /* We only use crc_rt to determine whether to force writes for updating
+         * the CRCs, so use a conservative tile size (16x16).
+         */
+        int crc_rt = GENX(pan_select_crc_rt)(fb, 16 * 16);
 
         bool always_write = false;
 

src/panfrost/lib/pan_cs.c

@@ -83,8 +83,22 @@ pan_sample_pattern(unsigned samples)
 }
 
 int
-GENX(pan_select_crc_rt)(const struct pan_fb_info *fb)
+GENX(pan_select_crc_rt)(const struct pan_fb_info *fb, unsigned tile_size)
 {
+        /* Disable CRC when the tile size is not 16x16. In the hardware, CRC
+         * tiles are the same size as the tiles of the framebuffer. However,
+         * our code only handles 16x16 tiles. Therefore under the current
+         * implementation, we must disable CRC when 16x16 tiles are not used.
+         *
+         * This may hurt performance. However, smaller tile sizes are rare, and
+         * CRCs are more expensive at smaller tile sizes, reducing the benefit.
+         * Restricting CRC to 16x16 should work in practice.
+         */
+        if (tile_size != 16 * 16) {
+                assert(tile_size < 16 * 16);
+                return -1;
+        }
+
 #if PAN_ARCH <= 6
         if (fb->rt_count == 1 && fb->rts[0].view && !fb->rts[0].discard &&
             fb->rts[0].view->image->layout.crc_mode != PAN_IMAGE_CRC_NONE)
@@ -636,7 +650,7 @@ GENX(pan_emit_fbd)(const struct panfrost_device *dev,
 
         unsigned tile_size;
         unsigned internal_cbuf_size = pan_internal_cbuf_size(fb, &tile_size);
-        int crc_rt = GENX(pan_select_crc_rt)(fb);
+        int crc_rt = GENX(pan_select_crc_rt)(fb, tile_size);
         bool has_zs_crc_ext = (fb->zs.view.zs || fb->zs.view.s || crc_rt >= 0);
 
         pan_section_pack(fbd, FRAMEBUFFER, PARAMETERS, cfg) {

src/panfrost/lib/pan_cs.h

@@ -149,7 +149,7 @@ GENX(pan_emit_tls)(const struct pan_tls_info *info,
                    void *out);
 
 int
-GENX(pan_select_crc_rt)(const struct pan_fb_info *fb);
+GENX(pan_select_crc_rt)(const struct pan_fb_info *fb, unsigned tile_size);
 
 unsigned
 GENX(pan_emit_fbd)(const struct panfrost_device *dev,