On 15/10/2025 12:41, Boris Brezillon wrote: > On Fri, 10 Oct 2025 15:50:58 +0100 > Steven Price <[email protected]> wrote: > >> On 10/10/2025 11:11, Boris Brezillon wrote: >>> Will be needed if we want to skip CPU cache maintenance operations when >>> the GPU can snoop CPU caches. >>> >>> v2: >>> - New commit >>> >>> Signed-off-by: Boris Brezillon <[email protected]> >>> --- >>> drivers/gpu/drm/panfrost/panfrost_device.h | 1 + >>> drivers/gpu/drm/panfrost/panfrost_drv.c | 1 + >>> drivers/gpu/drm/panfrost/panfrost_gpu.c | 18 +++++++++++++++++- >>> drivers/gpu/drm/panfrost/panfrost_regs.h | 2 ++ >>> include/uapi/drm/panfrost_drm.h | 7 +++++++ >>> 5 files changed, 28 insertions(+), 1 deletion(-) >>> >>> diff --git a/drivers/gpu/drm/panfrost/panfrost_device.h >>> b/drivers/gpu/drm/panfrost/panfrost_device.h >>> index 1e73efad02a8..bd38b7ae169e 100644 >>> --- a/drivers/gpu/drm/panfrost/panfrost_device.h >>> +++ b/drivers/gpu/drm/panfrost/panfrost_device.h >>> @@ -75,6 +75,7 @@ struct panfrost_features { >>> u32 thread_max_workgroup_sz; >>> u32 thread_max_barrier_sz; >>> u32 coherency_features; >>> + u32 selected_coherency; >>> 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 607a5b8448d0..3ffcd08f7745 100644 >>> --- a/drivers/gpu/drm/panfrost/panfrost_drv.c >>> +++ b/drivers/gpu/drm/panfrost/panfrost_drv.c >>> @@ -94,6 +94,7 @@ static int panfrost_ioctl_get_param(struct drm_device >>> *ddev, void *data, struct >>> PANFROST_FEATURE_ARRAY(JS_FEATURES, js_features, 15); >>> PANFROST_FEATURE(NR_CORE_GROUPS, nr_core_groups); >>> PANFROST_FEATURE(THREAD_TLS_ALLOC, thread_tls_alloc); >>> + PANFROST_FEATURE(SELECTED_COHERENCY, selected_coherency); >>> >>> case DRM_PANFROST_PARAM_SYSTEM_TIMESTAMP: >>> ret = panfrost_ioctl_query_timestamp(pfdev, ¶m->value); >>> diff --git a/drivers/gpu/drm/panfrost/panfrost_gpu.c >>> b/drivers/gpu/drm/panfrost/panfrost_gpu.c >>> index 174e190ba40f..fed323e6a307 100644 >>> --- a/drivers/gpu/drm/panfrost/panfrost_gpu.c >>> +++ b/drivers/gpu/drm/panfrost/panfrost_gpu.c >>> @@ -260,7 +260,23 @@ static void panfrost_gpu_init_features(struct >>> panfrost_device *pfdev) >>> pfdev->features.max_threads = gpu_read(pfdev, GPU_THREAD_MAX_THREADS); >>> 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); >>> + >>> + if (panfrost_has_hw_feature(pfdev, HW_FEATURE_COHERENCY_REG)) >>> + pfdev->features.coherency_features = gpu_read(pfdev, >>> GPU_COHERENCY_FEATURES); >>> + else >>> + pfdev->features.coherency_features = COHERENCY_ACE_LITE; >>> + >>> + if (!pfdev->coherent) { >>> + pfdev->features.selected_coherency = COHERENCY_NONE; >>> + } else if (pfdev->features.coherency_features & COHERENCY_ACE) { >>> + pfdev->features.selected_coherency = COHERENCY_ACE; >>> + } else if (pfdev->features.coherency_features & COHERENCY_ACE_LITE) { >>> + pfdev->features.selected_coherency = COHERENCY_ACE_LITE; >>> + } else { >>> + drm_WARN(pfdev->ddev, true, "No known coherency protocol >>> supported"); >>> + pfdev->features.selected_coherency = COHERENCY_NONE; >>> + } >> >> Same comment as for panthor about not using bits when we can't have more >> than one. But also here because selected_coherency is only a UAPI >> concept, it would make sense to use the UAPI values, i.e. >> DRM_PANFROST_GPU_COHERENCY_ACE_LITE etc rather than the private >> COHERENCY_ACE_LITE defines. > > For simplicity (we simply copy the coherency_features from the GPU reg > at the moment), I want the HW/uAPI values to match, so I've added > BUILD_BUG_ON()s. And I think I'd prefer to stick to the defs in > panfrost_regs.h, such that if we ever end up writing that back to > COHERENCY_ENABLE on newer HW, it's obvious we based the initialization > on those HW values.
Yeah, BUILD_BUG_ON works as well. It just seemed a little fragile to be using the 'wrong' symbol - and we're messed these symbols up before ;) >> >> Although there is actually a COHERENCY_ENABLE register on some GPUs >> (BASE_HW_FEATURE_COHERENCY_REG in the kbase driver). Looks like it was >> probably introduced for Bifrost. But AFAIK the above checks should be ok. > > Yep. I didn't dare writing it back, because it's working as-is on all > supported HW, and I don't want to regress things. Not that I've played > with this COHERENCY_ENABLE reg on my amlogic board, which is coherent, > to fake a non-coherent setup, and it works like a charm :-). > Yeah, I don't know if it's actually useful beyond testing the non-coherent mode, so probably not worth changing things. Thanks, Steve
