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[2620:137:e000::3:5]) by mx.google.com with ESMTPS id w191-20020a6382c8000000b0059b9e4e53d5si9180377pgd.218.2023.10.24.17.54.27 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 24 Oct 2023 17:54:27 -0700 (PDT) Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::3:5 as permitted sender) client-ip=2620:137:e000::3:5; Authentication-Results: mx.google.com; dkim=fail header.i=@igalia.com header.s=20170329 header.b=OrClVTCZ; spf=pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::3:5 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: from out1.vger.email (depot.vger.email [IPv6:2620:137:e000::3:0]) by groat.vger.email (Postfix) with ESMTP id 3CF3A804C531; Tue, 24 Oct 2023 17:54:24 -0700 (PDT) X-Virus-Status: Clean X-Virus-Scanned: clamav-milter 0.103.10 at groat.vger.email Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232011AbjJYAyG (ORCPT + 26 others); Tue, 24 Oct 2023 20:54:06 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:39514 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231433AbjJYAx7 (ORCPT ); Tue, 24 Oct 2023 20:53:59 -0400 Received: from fanzine2.igalia.com (fanzine.igalia.com [178.60.130.6]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id AB5EA10E7 for ; Tue, 24 Oct 2023 17:53:54 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=igalia.com; s=20170329; h=Content-Transfer-Encoding:Content-Type:MIME-Version:References: In-Reply-To:Message-ID:Date:Subject:Cc:To:From:Sender:Reply-To:Content-ID: Content-Description:Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc :Resent-Message-ID:List-Id:List-Help:List-Unsubscribe:List-Subscribe: List-Post:List-Owner:List-Archive; bh=ptMecIWhxppUkq2aXoZa2CHrMXZa5VzlLHDPQoyEpAg=; b=OrClVTCZX7Ue/kAEL5KE0PbLo0 T5rBz0LCKIV0u9EhorjmSHrK/I2GsDpHz4hehUYHXr0SfGRpp86Zn6cF1EgD48DwZMgm41AW40nCC Fh93+/G6I9+CILBb0D9fb3G/bq6g2ZhiEEXORCHd6yjrGocodEeyqgGByRmWnrdLHtDZb9WhRfs2I 5vEJnp8tVghSkjIF3pj3pykoCH8aJOfT3Q4/Bhnw7yaP8ynG5CHOQ+nZqwzT5E6wA//Y4PtTeoKAs 1fuOer0ETIIGxT6QEgEAoJtcGuLFccnidF9aDXi5J56qydss64qUhhu1PFZbjtODkN1c4bCUykkbO LEuP7SOQ==; Received: from [191.193.179.125] (helo=steammachine.lan) by fanzine2.igalia.com with esmtpsa (Cipher TLS1.3:ECDHE_X25519__RSA_PSS_RSAE_SHA256__AES_256_GCM:256) (Exim) id 1qvS9f-006qog-Uh; Wed, 25 Oct 2023 02:53:52 +0200 From: =?utf-8?q?Andr=C3=A9_Almeida?= To: dri-devel@lists.freedesktop.org, amd-gfx@lists.freedesktop.org, linux-kernel@vger.kernel.org Cc: kernel-dev@igalia.com, alexander.deucher@amd.com, christian.koenig@amd.com, pierre-eric.pelloux-prayer@amd.com, Simon Ser , Rob Clark , Pekka Paalanen , Daniel Vetter , Daniel Stone , =?utf-8?b?J01hcmVrIE9sxaHDoWsn?= , Dave Airlie , =?utf-8?q?Michel_D=C3=A4nzer?= , Randy Dunlap , Pekka Paalanen , =?utf-8?q?Andr=C3=A9_Almeida?= Subject: [PATCH v8 5/6] drm/doc: Define KMS atomic state set Date: Tue, 24 Oct 2023 21:53:17 -0300 Message-ID: <20231025005318.293690-6-andrealmeid@igalia.com> X-Mailer: git-send-email 2.42.0 In-Reply-To: <20231025005318.293690-1-andrealmeid@igalia.com> References: <20231025005318.293690-1-andrealmeid@igalia.com> MIME-Version: 1.0 X-Spam-Status: No, score=-0.6 required=5.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS autolearn=unavailable autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on groat.vger.email Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org X-Greylist: Sender passed SPF test, not delayed by milter-greylist-4.6.4 (groat.vger.email [0.0.0.0]); Tue, 24 Oct 2023 17:54:24 -0700 (PDT) X-getmail-retrieved-from-mailbox: INBOX X-GMAIL-THRID: 1780686801243247365 X-GMAIL-MSGID: 1780686801243247365 From: Pekka Paalanen Specify how the atomic state is maintained between userspace and kernel, plus the special case for async flips. Signed-off-by: Pekka Paalanen Signed-off-by: André Almeida --- v8: - no changes v7: - add a note that drivers can make exceptions for ad-hoc prop changes - add a note about flipping the same FB_ID as a no-op --- --- Documentation/gpu/drm-uapi.rst | 47 ++++++++++++++++++++++++++++++++++ 1 file changed, 47 insertions(+) diff --git a/Documentation/gpu/drm-uapi.rst b/Documentation/gpu/drm-uapi.rst index 632989df3727..34bd02270ee7 100644 --- a/Documentation/gpu/drm-uapi.rst +++ b/Documentation/gpu/drm-uapi.rst @@ -570,3 +570,50 @@ dma-buf interoperability Please see Documentation/userspace-api/dma-buf-alloc-exchange.rst for information on how dma-buf is integrated and exposed within DRM. + +KMS atomic state +================ + +An atomic commit can change multiple KMS properties in an atomic fashion, +without ever applying intermediate or partial state changes. Either the whole +commit succeeds or fails, and it will never be applied partially. This is the +fundamental improvement of the atomic API over the older non-atomic API which is +referred to as the "legacy API". Applying intermediate state could unexpectedly +fail, cause visible glitches, or delay reaching the final state. + +An atomic commit can be flagged with DRM_MODE_ATOMIC_TEST_ONLY, which means the +complete state change is validated but not applied. Userspace should use this +flag to validate any state change before asking to apply it. If validation fails +for any reason, userspace should attempt to fall back to another, perhaps +simpler, final state. This allows userspace to probe for various configurations +without causing visible glitches on screen and without the need to undo a +probing change. + +The changes recorded in an atomic commit apply on top the current KMS state in +the kernel. Hence, the complete new KMS state is the complete old KMS state with +the committed property settings done on top. The kernel will try to avoid +no-operation changes, so it is safe for userspace to send redundant property +settings. However, not every situation allows for no-op changes, due to the +need to acquire locks for some attributes. Userspace needs to be aware that some +redundant information might result in oversynchronization issues. No-operation +changes do not count towards actually needed changes, e.g. setting MODE_ID to a +different blob with identical contents as the current KMS state shall not be a +modeset on its own. As a special exception for VRR needs, explicitly setting +FB_ID to its current value is not a no-op. + +A "modeset" is a change in KMS state that might enable, disable, or temporarily +disrupt the emitted video signal, possibly causing visible glitches on screen. A +modeset may also take considerably more time to complete than other kinds of +changes, and the video sink might also need time to adapt to the new signal +properties. Therefore a modeset must be explicitly allowed with the flag +DRM_MODE_ATOMIC_ALLOW_MODESET. This in combination with +DRM_MODE_ATOMIC_TEST_ONLY allows userspace to determine if a state change is +likely to cause visible disruption on screen and avoid such changes when end +users do not expect them. + +An atomic commit with the flag DRM_MODE_PAGE_FLIP_ASYNC is allowed to +effectively change only the FB_ID property on any planes. No-operation changes +are ignored as always. Changing any other property will cause the commit to be +rejected. Each driver may relax this restriction if they have guarantees that +such property change doesn't cause modesets. Userspace can use TEST_ONLY commits +to query the driver about this.