From mboxrd@z Thu Jan 1 00:00:00 1970 From: Ville =?iso-8859-1?Q?Syrj=E4l=E4?= Subject: Re: [RFC PATCH 18/20] lib: image-formats: Add v4l2 formats support Date: Thu, 21 Mar 2019 23:44:55 +0200 Message-ID: <20190321214455.GL3888@intel.com> References: <20190320142739.GK3888@intel.com> <20190320160939.GR3888@intel.com> <20190320164133.GT3888@intel.com> <20190320183914.GV3888@intel.com> <46df4fb13636b90c147839b0aa5ad1ac33030461.camel@bootlin.com> <20190321163532.GG3888@intel.com> Mime-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Transfer-Encoding: 8bit Return-path: Content-Disposition: inline In-Reply-To: Sender: linux-kernel-owner@vger.kernel.org To: Nicolas Dufresne Cc: Paul Kocialkowski , Maxime Ripard , Daniel Vetter , David Airlie , Maarten Lankhorst , Sean Paul , Mauro Carvalho Chehab , Sakari Ailus , linux-kernel@vger.kernel.org, dri-devel@lists.freedesktop.org, Hans Verkuil , Laurent Pinchart , Thomas Petazzoni , linux-media@vger.kernel.org, Daniel Stone List-Id: dri-devel@lists.freedesktop.org On Thu, Mar 21, 2019 at 03:14:06PM -0400, Nicolas Dufresne wrote: > Le jeudi 21 mars 2019 ā 18:35 +0200, Ville Syrjälä a écrit : > > > I'm not sure what it's worth, but there is a "pixel format guide" > > > project that is all about matching formats from one API to another: > > > https://afrantzis.com/pixel-format-guide/ (and it has an associated > > > tool too). > > > > > > On the page about DRM, it seems that they got the word that DRM formats > > > are the native pixel order in little-endian systems: > > > https://afrantzis.com/pixel-format-guide/drm.html > > > > Looks consistent with the official word in drm_fourcc.h. > > > > $ python3 -m pfg find-compatible V4L2_PIX_FMT_XBGR32 drm > > Format: V4L2_PIX_FMT_XBGR32 > > Is compatible on all systems with: > > DRM_FORMAT_XRGB8888 > > Is compatible on little-endian systems with: > > Is compatible on big-endian systems with: > > > > $ python3 -m pfg find-compatible DRM_FORMAT_XRGB8888 v4l2 > > Format: DRM_FORMAT_XRGB8888 > > Is compatible on all systems with: > > V4L2_PIX_FMT_XBGR32 > > Is compatible on little-endian systems with: > > Is compatible on big-endian systems with: > > > > Even works both ways :) > > > > > Perhaps some drivers have been abusing the format definitions, leading > > > to the inconsistencies that Nicolas could witness? > > > > That is quite possible, perhaps even likely. No one really > > seems interested in making sure big endian systems actually > > work properly. I believe the usual approach is to hack > > around semi-rnadomly until the correct colors accidentally > > appear on the screen. > > We did not hack around randomly. The code in GStreamer is exactly what > the DRM and Wayland dev told us to do (they provided the initial > patches to make it work). These are initially patches from Intel for > what it's worth (see the wlvideoformat.c header [0]). Even though I > just notice that in this file, it seems that we ended up with a > different mapping order for WL and DRM format in 24bit RGB (no > padding), clearly is a bug. That being said, there is no logical > meaning for little endian 24bit RGB, you can't load a pixel on CPU in a > single op. To me little endian just means "little end comes first". So if you think of things as just a stream of bytes CPU word size etc. doesn't matter. And I guess if you really wanted to you could even make a CPU with 24bit word size. Anyways, to make things more clear drm_fourcc.h could probably document things better by showing explicitly which bits go into which byte. I don't know who did what patches for whatever project, but clearly something has been lost in translation at some point. > Just saying since I would not know which one of the two > mapping here is right. I would probably have to go testing what DRM > drivers do, which may not mean anything. I would also ask and get > contradictory answers. > > I have never myself tested these on big endian drivers though, as you > say, nobody seems to care about graphics on those anymore. So the easy > statement is to say they are little endian, like you just did, and > ignore the legacy, but there is some catch. YUV formats has been added > without applying this rules. All drm formats follow the same rule (ignoring the recently added non-byte aligned stuff which I guess don't really follow any rules). > So V4L2 YUYV match YUYV in DRM format name > instead of little endian UYVY. (at least 4 tested drivers implements it > this way). Same for NV12, for which little endian CPU representation > would swap the UV paid on a 16bit word. DRM NV12 and YUYV (YUY2) match the NV12 and YUY2 defined here https://docs.microsoft.com/en-us/windows/desktop/medfound/recommended-8-bit-yuv-formats-for-video-rendering > > To me, all the YUV stuff is the right way, because this is what the > rest of the world is doing, it's not ambiguous. > > [0] https://gitlab.freedesktop.org/gstreamer/gst-plugins-bad/blob/master/ext/wayland/wlvideoformat.c#L86 > > > > Nicolas -- Ville Syrjälä Intel