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[109.191.228.208]) by smtp.gmail.com with ESMTPSA id a11sm7706080lff.68.2018.12.27.15.26.56 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Thu, 27 Dec 2018 15:26:57 -0800 (PST) Message-ID: <00547df7d87c7fe6d8c842d5b29a0cd6809cdf5d.camel@gmail.com> Subject: Re: [RFC PATCH 1/2] drm/fb-helper: Bring back workaround for bugs of SDL 1.2 From: Ivan Mironov To: Daniel Vetter Cc: dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org, Maarten Lankhorst , Maxime Ripard , Sean Paul , David Airlie , saahriktu , Eugeniy Paltsev Date: Fri, 28 Dec 2018 04:26:56 +0500 In-Reply-To: <20181227120046.GC9058@dvetter-linux.ger.corp.intel.com> References: <20181226121124.1632-1-mironov.ivan@gmail.com> <20181226121124.1632-2-mironov.ivan@gmail.com> <20181227120046.GC9058@dvetter-linux.ger.corp.intel.com> Content-Type: text/plain; charset="UTF-8" User-Agent: Evolution 3.30.3 (3.30.3-1.fc29) Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, 2018-12-27 at 13:00 +0100, Daniel Vetter wrote: > > + /* > > + * Workaround for SDL 1.2, which is known to be setting all pixel format > > + * fields values to zero in some cases. We treat this situation as a > > + * kind of "use some reasonable autodetected values". > > + */ > > + if (!var->red.offset && !var->green.offset && > > + !var->blue.offset && !var->transp.offset && > > + !var->red.length && !var->green.length && > > + !var->blue.length && !var->transp.length && > > + !var->red.msb_right && !var->green.msb_right && > > + !var->blue.msb_right && !var->transp.msb_right) { > > + u8 depth; > > + > > + /* > > + * There is no way to guess the right value for depth when > > + * bpp is 16 or 32. So we just restore the behaviour previously > > + * introduced here by commit 785b93ef8c309. In fact, this was > > + * implemented even earlier in various device drivers. > > + */ > > + switch (var->bits_per_pixel) { > > + case 16: > > + depth = 15; > > + break; > > + case 32: > > + depth = 24; > > + break; > > + default: > > + depth = var->bits_per_pixel; > > + break; > > + } > > The guesswork here looks fishy. We should still have the drm-side format, > and should use that. This existed for a very long time until problematic commit was applied. And there is a clear evidence that it was actually used by applications. > Otherwise the patches look good I think, but they > need a Fixes: tag and cc: stable so backporters know what to do with > these. > I added "cc: stable" into the regression fix. Also added more info into the commit messages. See the PATCH v1 in the mailing list. Thanks.