From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from gabe.freedesktop.org (gabe.freedesktop.org [131.252.210.177]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 24F33CCD18E for ; Wed, 15 Oct 2025 13:18:37 +0000 (UTC) Received: from gabe.freedesktop.org (localhost [127.0.0.1]) by gabe.freedesktop.org (Postfix) with ESMTP id 78E3A10E184; Wed, 15 Oct 2025 13:18:36 +0000 (UTC) Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by gabe.freedesktop.org (Postfix) with ESMTP id DADEB10E184 for ; Wed, 15 Oct 2025 13:18:34 +0000 (UTC) Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 955B3106F; Wed, 15 Oct 2025 06:18:26 -0700 (PDT) Received: from [10.1.31.33] (e122027.cambridge.arm.com [10.1.31.33]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 965E13F6A8; Wed, 15 Oct 2025 06:18:31 -0700 (PDT) Message-ID: <982d0fb9-a987-4b7f-ba9d-1a87b19e275f@arm.com> Date: Wed, 15 Oct 2025 14:18:29 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 09/13] drm/panfrost: Expose the selected coherency protocol to the UMD To: Boris Brezillon Cc: Liviu Dudau , =?UTF-8?Q?Adri=C3=A1n_Larumbe?= , dri-devel@lists.freedesktop.org, Maarten Lankhorst , Maxime Ripard , Thomas Zimmermann , David Airlie , Simona Vetter , Faith Ekstrand , kernel@collabora.com References: <20251010101147.3290604-1-boris.brezillon@collabora.com> <20251010101147.3290604-10-boris.brezillon@collabora.com> <2e85c917-4e49-4cb2-ba2c-edb35907860d@arm.com> <20251015134159.74b42ec4@fedora> From: Steven Price Content-Language: en-GB In-Reply-To: <20251015134159.74b42ec4@fedora> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-BeenThere: dri-devel@lists.freedesktop.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Direct Rendering Infrastructure - Development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: dri-devel-bounces@lists.freedesktop.org Sender: "dri-devel" On 15/10/2025 12:41, Boris Brezillon wrote: > On Fri, 10 Oct 2025 15:50:58 +0100 > Steven Price 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 >>> --- >>> 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