diff options
Diffstat (limited to 'include/drm/drm_cache.h')
| -rw-r--r-- | include/drm/drm_cache.h | 18 |
1 files changed, 18 insertions, 0 deletions
diff --git a/include/drm/drm_cache.h b/include/drm/drm_cache.h index cebecff536a3..c5fb6f871930 100644 --- a/include/drm/drm_cache.h +++ b/include/drm/drm_cache.h @@ -41,6 +41,24 @@ static inline bool drm_arch_can_wc_memory(void) return false; #elif defined(CONFIG_MIPS) && defined(CONFIG_CPU_LOONGSON3) return false; +#elif defined(CONFIG_ARM) || defined(CONFIG_ARM64) + /* + * The DRM driver stack is designed to work with cache coherent devices + * only, but permits an optimization to be enabled in some cases, where + * for some buffers, both the CPU and the GPU use uncached mappings, + * removing the need for DMA snooping and allocation in the CPU caches. + * + * The use of uncached GPU mappings relies on the correct implementation + * of the PCIe NoSnoop TLP attribute by the platform, otherwise the GPU + * will use cached mappings nonetheless. On x86 platforms, this does not + * seem to matter, as uncached CPU mappings will snoop the caches in any + * case. However, on ARM and arm64, enabling this optimization on a + * platform where NoSnoop is ignored results in loss of coherency, which + * breaks correct operation of the device. Since we have no way of + * detecting whether NoSnoop works or not, just disable this + * optimization entirely for ARM and arm64. + */ + return false; #else return true; #endif |