[PATCH v2] drm/panfrost: Add AFBC_FEATURES parameter

[PATCH v2] drm/panfrost: Add AFBC_FEATURES parameter

[Alyssa Rosenzweig]

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 {
-- 
2.30.2