nvk: Add an NVK_DEBUG=coherent flag

Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/38163>

docs/drivers/nvk.rst

@@ -72,6 +72,9 @@ specific to NVK:
       views.
    ``gart``
       Forces all memory to be allocated from system RAM (GART)
+   ``coherent``
+      Forces all memory maps to be coherent with the CPU caches.  This only
+      applies to Tegra devices.
 
 .. envvar:: NVK_I_WANT_A_BROKEN_VULKAN_DRIVER
 

src/nouveau/vulkan/nvk_debug.h

@@ -39,6 +39,9 @@ enum nvk_debug {
 
    /* Force all memory allocations to go to GART */
    NVK_DEBUG_FORCE_GART = 1ull << 7,
+
+   /* Force all memory allocations to go to GART */
+   NVK_DEBUG_FORCE_COHERENT = 1ull << 8,
 };
 
 #endif /* NVK_DEBUG_H */

src/nouveau/vulkan/nvk_instance.c

@@ -89,6 +89,7 @@ nvk_init_debug_flags(struct nvk_instance *instance)
       { "no_cbuf", NVK_DEBUG_NO_CBUF },
       { "edb_bview", NVK_DEBUG_FORCE_EDB_BVIEW },
       { "gart", NVK_DEBUG_FORCE_GART },
+      { "coherent", NVK_DEBUG_FORCE_COHERENT },
       { NULL, 0 },
    };
 

src/nouveau/vulkan/nvkmd/nouveau/nvkmd_nouveau_mem.c

@@ -135,6 +135,9 @@ nvkmd_nouveau_alloc_tiled_mem(struct nvkmd_dev *_dev,
       nouveau_flags |= NOUVEAU_WS_BO_NO_SHARE;
 
    if (dev->base.pdev->dev_info.type == NV_DEVICE_TYPE_SOC) {
+      if (dev->base.pdev->debug_flags & NVK_DEBUG_FORCE_COHERENT)
+         flags |= NVKMD_MEM_COHERENT;
+
       /* On Tegra, we have to explicitly request coherent maps by putting the
        * BO in NOUVEAU_GEM_DOMAIN_COHERENT.
        */