The value of the AFBC_FEATURES register is required by userspace to determine AFBC support on Bifrost. A user on our IRC channel (#panfrost) reported a workload that raised a fault on one system's Mali G31 but worked flawlessly with another system's Mali G31. We determined the cause to be missing AFBC support on one vendor's Mali implementation -- it turns out AFBC is optional on Bifrost!
Whether AFBC is supported or not is exposed in the AFBC_FEATURES register on Bifrost, which reads back as 0 on Midgard. A zero value indicates AFBC is fully supported, provided the architecture itself supports AFBC, allowing backwards-compatibility with Midgard. Bits 0 and 15 indicate that AFBC support is absent for texturing and rendering respectively.
The user experiencing the fault reports that AFBC_FEATURES reads back 0x10001 on their system, confirming the architectural lack of AFBC. Userspace needs this this parameter to know to disable AFBC on that chip, and perhaps others.
v2: Fix typo from copy-paste fail.
Signed-off-by: Alyssa Rosenzweig alyssa.rosenzweig@collabora.com Cc: Rob Herring robh@kernel.org Cc: Tomeu Vizoso tomeu.vizoso@collabora.com Cc: Steven Price steven.price@arm.com --- drivers/gpu/drm/panfrost/panfrost_device.h | 1 + drivers/gpu/drm/panfrost/panfrost_drv.c | 1 + drivers/gpu/drm/panfrost/panfrost_gpu.c | 1 + drivers/gpu/drm/panfrost/panfrost_regs.h | 1 + include/uapi/drm/panfrost_drm.h | 1 + 5 files changed, 5 insertions(+)
diff --git a/drivers/gpu/drm/panfrost/panfrost_device.h b/drivers/gpu/drm/panfrost/panfrost_device.h index 597cf1459..f614e9877 100644 --- a/drivers/gpu/drm/panfrost/panfrost_device.h +++ b/drivers/gpu/drm/panfrost/panfrost_device.h @@ -45,6 +45,7 @@ struct panfrost_features { u32 thread_max_workgroup_sz; u32 thread_max_barrier_sz; u32 coherency_features; + u32 afbc_features; u32 texture_features[4]; u32 js_features[16];
diff --git a/drivers/gpu/drm/panfrost/panfrost_drv.c b/drivers/gpu/drm/panfrost/panfrost_drv.c index ca07098a6..3383c8200 100644 --- a/drivers/gpu/drm/panfrost/panfrost_drv.c +++ b/drivers/gpu/drm/panfrost/panfrost_drv.c @@ -63,6 +63,7 @@ static int panfrost_ioctl_get_param(struct drm_device *ddev, void *data, struct PANFROST_FEATURE(THREAD_MAX_BARRIER_SZ, thread_max_barrier_sz); PANFROST_FEATURE(COHERENCY_FEATURES, coherency_features); + PANFROST_FEATURE(AFBC_FEATURES, afbc_features); PANFROST_FEATURE_ARRAY(TEXTURE_FEATURES, texture_features, 3); PANFROST_FEATURE_ARRAY(JS_FEATURES, js_features, 15); PANFROST_FEATURE(NR_CORE_GROUPS, nr_core_groups); diff --git a/drivers/gpu/drm/panfrost/panfrost_gpu.c b/drivers/gpu/drm/panfrost/panfrost_gpu.c index 2aae636f1..0e70e27fd 100644 --- a/drivers/gpu/drm/panfrost/panfrost_gpu.c +++ b/drivers/gpu/drm/panfrost/panfrost_gpu.c @@ -228,6 +228,7 @@ static void panfrost_gpu_init_features(struct panfrost_device *pfdev) pfdev->features.thread_max_workgroup_sz = gpu_read(pfdev, GPU_THREAD_MAX_WORKGROUP_SIZE); pfdev->features.thread_max_barrier_sz = gpu_read(pfdev, GPU_THREAD_MAX_BARRIER_SIZE); pfdev->features.coherency_features = gpu_read(pfdev, GPU_COHERENCY_FEATURES); + pfdev->features.afbc_features = gpu_read(pfdev, GPU_AFBC_FEATURES); for (i = 0; i < 4; i++) pfdev->features.texture_features[i] = gpu_read(pfdev, GPU_TEXTURE_FEATURES(i));
diff --git a/drivers/gpu/drm/panfrost/panfrost_regs.h b/drivers/gpu/drm/panfrost/panfrost_regs.h index eddaa62ad..dc9df5457 100644 --- a/drivers/gpu/drm/panfrost/panfrost_regs.h +++ b/drivers/gpu/drm/panfrost/panfrost_regs.h @@ -82,6 +82,7 @@
#define GPU_TEXTURE_FEATURES(n) (0x0B0 + ((n) * 4)) #define GPU_JS_FEATURES(n) (0x0C0 + ((n) * 4)) +#define GPU_AFBC_FEATURES (0x4C) /* (RO) AFBC support on Bifrost */
#define GPU_SHADER_PRESENT_LO 0x100 /* (RO) Shader core present bitmap, low word */ #define GPU_SHADER_PRESENT_HI 0x104 /* (RO) Shader core present bitmap, high word */ diff --git a/include/uapi/drm/panfrost_drm.h b/include/uapi/drm/panfrost_drm.h index ec19db1ee..061e700dd 100644 --- a/include/uapi/drm/panfrost_drm.h +++ b/include/uapi/drm/panfrost_drm.h @@ -171,6 +171,7 @@ enum drm_panfrost_param { DRM_PANFROST_PARAM_JS_FEATURES15, DRM_PANFROST_PARAM_NR_CORE_GROUPS, DRM_PANFROST_PARAM_THREAD_TLS_ALLOC, + DRM_PANFROST_PARAM_AFBC_FEATURES, };
struct drm_panfrost_get_param {