From patchwork Tue Sep 17 17:24:20 2019 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Simon Ser X-Patchwork-Id: 11149235 Return-Path: Received: from mail.kernel.org (pdx-korg-mail-1.web.codeaurora.org [172.30.200.123]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id 2591914DB for ; Tue, 17 Sep 2019 17:24:35 +0000 (UTC) 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 mail.kernel.org (Postfix) with ESMTPS id 0E03A218AE for ; Tue, 17 Sep 2019 17:24:35 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 0E03A218AE Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=emersion.fr Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=dri-devel-bounces@lists.freedesktop.org Received: from gabe.freedesktop.org (localhost [127.0.0.1]) by gabe.freedesktop.org (Postfix) with ESMTP id C515D6ED15; Tue, 17 Sep 2019 17:24:32 +0000 (UTC) X-Original-To: dri-devel@lists.freedesktop.org Delivered-To: dri-devel@lists.freedesktop.org X-Greylist: delayed 115018 seconds by postgrey-1.36 at gabe; Tue, 17 Sep 2019 17:24:30 UTC Received: from mail-40132.protonmail.ch (mail-40132.protonmail.ch [185.70.40.132]) by gabe.freedesktop.org (Postfix) with ESMTPS id 576296ED15 for ; Tue, 17 Sep 2019 17:24:30 +0000 (UTC) Date: Tue, 17 Sep 2019 17:24:20 +0000 To: dri-devel@lists.freedesktop.org From: Simon Ser Subject: [PATCH v2] drm: two planes with the same zpos have undefined ordering Message-ID: <1hklN2_EspD_s4vA3fdCCkVN9jeARGhmtkSGWDyVus-0ryZFs4xftUYRp_Z4pzsikJActaDVaTUoPNfBd-QitQX_JJTXkkqKFXxJhgMjEI0=@emersion.fr> In-Reply-To: References: <20190910133810.64e973f4@eldfell.localdomain> Feedback-ID: FsVprHBOgyvh0T8bxcZ0CmvJCosWkwVUg658e_lOUQMnA9qynD8O1lGeniuBDfPSkDAUuhiKfOIXUZBfarMyvA==:Ext:ProtonMail MIME-Version: 1.0 X-Spam-Status: No, score=-1.2 required=7.0 tests=ALL_TRUSTED,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF autolearn=ham autolearn_force=no version=3.4.2 X-Spam-Checker-Version: SpamAssassin 3.4.2 (2018-09-13) on mail.protonmail.ch X-Mailman-Original-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=emersion.fr; s=protonmail; t=1568741067; bh=XwlxkzMlUCQgqE276URVdlsNfavanldGs+g2WWWmFqw=; h=Date:To:From:Cc:Reply-To:Subject:In-Reply-To:References: Feedback-ID:From; b=Ynd0xUvSkUdvkZxbu+nmvl/swxTByMZ8L28J3RHnLVuAEWl3HCLnPKcJ0jCkVePv0 BECsLUwMYb0pYglDCkWzrIHh4go+MbJsjmKnbYUOE0el847ykfqFOhL52FciiY3asC lsLpYJGMDVaukwUN3ma65UwxKHlia51WtOxNLdng= X-BeenThere: dri-devel@lists.freedesktop.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: Direct Rendering Infrastructure - Development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Reply-To: Simon Ser Cc: Daniel Vetter , Marius Vlad Errors-To: dri-devel-bounces@lists.freedesktop.org Sender: "dri-devel" Currently the property docs don't specify whether it's okay for two planes to have the same zpos value and what user-space should expect in this case. The rule mentionned in the past was to disambiguate with object IDs. However some drivers break this rule (that's why the ordering is documented as unspecified in case the zpos property is missing). Additionally it doesn't really make sense for a driver to user identical zpos values if it knows their relative position: the driver can just pick different values instead. So two solutions would make sense: either disallow completely identical zpos values for two different planes, either make the ordering unspecified. To allow drivers that don't know the relative ordering between two planes to still expose the zpos property, choose the latter solution. Additionally, update the drm_plane_state.zpos docs to clarify that zpos disambiguation via plane object IDs is a recommendation for drivers, not something user-space can rely on. v2: clarify drm_plane_state.zpos docs (Daniel) Signed-off-by: Simon Ser Cc: Pekka Paalanen Cc: Marius Vlad Cc: Daniel Vetter --- drivers/gpu/drm/drm_blend.c | 8 ++++---- include/drm/drm_plane.h | 6 +++--- 2 files changed, 7 insertions(+), 7 deletions(-) -- 2.23.0 diff --git a/drivers/gpu/drm/drm_blend.c b/drivers/gpu/drm/drm_blend.c index d02709dd2d4a..51bd5454e50a 100644 --- a/drivers/gpu/drm/drm_blend.c +++ b/drivers/gpu/drm/drm_blend.c @@ -132,10 +132,10 @@ * planes. Without this property the primary plane is always below the cursor * plane, and ordering between all other planes is undefined. The positive * Z axis points towards the user, i.e. planes with lower Z position values - * are underneath planes with higher Z position values. Note that the Z - * position value can also be immutable, to inform userspace about the - * hard-coded stacking of overlay planes, see - * drm_plane_create_zpos_immutable_property(). + * are underneath planes with higher Z position values. Two planes with the + * same Z position value have undefined ordering. Note that the Z position + * value can also be immutable, to inform userspace about the hard-coded + * stacking of overlay planes, see drm_plane_create_zpos_immutable_property(). * * pixel blend mode: * Pixel blend mode is set up with drm_plane_create_blend_mode_property(). diff --git a/include/drm/drm_plane.h b/include/drm/drm_plane.h index cd5903ad33f7..7ac68057b19d 100644 --- a/include/drm/drm_plane.h +++ b/include/drm/drm_plane.h @@ -141,9 +141,9 @@ struct drm_plane_state { * Priority of the given plane on crtc (optional). * * Note that multiple active planes on the same crtc can have an - * identical zpos value. The rule to solving the conflict is to compare - * the plane object IDs; the plane with a higher ID must be stacked on - * top of a plane with a lower ID. + * identical zpos value. To solve the conflict, the recommendation to + * drivers to avoid surprises is to compare the plane object IDs; the + * plane with a higher ID is stacked on top of a plane with a lower ID. * * See drm_plane_create_zpos_property() and * drm_plane_create_zpos_immutable_property() for more details.