drm/nouveau/device: fix changing endianess code to work on older GPUs
With this we try to detect if the endianess switch works and assume LE if
not. Suggested by Ben.
Fixes: 51c05340e407 ("drm/nouveau/device: detect if changing endianness failed")
Signed-off-by: Karol Herbst <kherbst@redhat.com>
Cc: <stable@vger.kernel.org> # v5.8+
Signed-off-by: Ben Skeggs <bskeggs@redhat.com>
diff --git a/drivers/gpu/drm/nouveau/nvkm/engine/device/base.c b/drivers/gpu/drm/nouveau/nvkm/engine/device/base.c
index dcb7067..7851bec 100644
--- a/drivers/gpu/drm/nouveau/nvkm/engine/device/base.c
+++ b/drivers/gpu/drm/nouveau/nvkm/engine/device/base.c
@@ -2924,17 +2924,34 @@
}
}
+/* returns true if the GPU is in the CPU native byte order */
static inline bool
nvkm_device_endianness(struct nvkm_device *device)
{
- u32 boot1 = nvkm_rd32(device, 0x000004) & 0x01000001;
#ifdef __BIG_ENDIAN
- if (!boot1)
- return false;
+ const bool big_endian = true;
#else
- if (boot1)
- return false;
+ const bool big_endian = false;
#endif
+
+ /* Read NV_PMC_BOOT_1, and assume non-functional endian switch if it
+ * doesn't contain the expected values.
+ */
+ u32 pmc_boot_1 = nvkm_rd32(device, 0x000004);
+ if (pmc_boot_1 && pmc_boot_1 != 0x01000001)
+ return !big_endian; /* Assume GPU is LE in this case. */
+
+ /* 0 means LE and 0x01000001 means BE GPU. Condition is true when
+ * GPU/CPU endianness don't match.
+ */
+ if (big_endian == !pmc_boot_1) {
+ nvkm_wr32(device, 0x000004, 0x01000001);
+ nvkm_rd32(device, 0x000000);
+ if (nvkm_rd32(device, 0x000004) != (big_endian ? 0x01000001 : 0x00000000))
+ return !big_endian; /* Assume GPU is LE on any unexpected read-back. */
+ }
+
+ /* CPU/GPU endianness should (hopefully) match. */
return true;
}
@@ -2987,14 +3004,10 @@
if (detect) {
/* switch mmio to cpu's native endianness */
if (!nvkm_device_endianness(device)) {
- nvkm_wr32(device, 0x000004, 0x01000001);
- nvkm_rd32(device, 0x000000);
- if (!nvkm_device_endianness(device)) {
- nvdev_error(device,
- "GPU not supported on big-endian\n");
- ret = -ENOSYS;
- goto done;
- }
+ nvdev_error(device,
+ "Couldn't switch GPU to CPUs endianess\n");
+ ret = -ENOSYS;
+ goto done;
}
boot0 = nvkm_rd32(device, 0x000000);
