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[92.176.231.205]) by smtp.gmail.com with ESMTPSA id a14-20020a5d456e000000b0022ccae2fa62sm1423311wrc.22.2022.10.13.00.39.22 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 13 Oct 2022 00:39:22 -0700 (PDT) Message-ID: Date: Thu, 13 Oct 2022 09:39:21 +0200 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.3.1 Subject: Re: [PATCH v4 5/5] drm/ofdrm: Support big-endian scanout buffers Content-Language: en-US To: =?UTF-8?Q?Michal_Such=c3=a1nek?= , Arnd Bergmann Cc: Thomas Zimmermann , David Airlie , Daniel Vetter , Helge Deller , Maxime Ripard , sam@ravnborg.org, Michael Ellerman , benh@kernel.crashing.org, Paul Mackerras , Geert Uytterhoeven , mark.cave-ayland@ilande.co.uk, linux-fbdev@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, dri-devel@lists.freedesktop.org References: <83071743-a7f2-f761-baa3-da688f26b5e3@suse.de> <9162f41f-28c3-493c-ab54-b1c4a2fdf494@app.fastmail.com> <654e3cfe-80d7-46c9-8e5e-461846e4df35@app.fastmail.com> <866c7033-0d4e-7b5d-008c-8eb16f99498b@suse.de> <0a15ecf5-939d-3b00-bcde-0fc7b449cfda@suse.de> <76d8a408-fc3e-4bd1-91c5-8278f7469979@app.fastmail.com> <20221012142707.GD28810@kitsune.suse.cz> From: Javier Martinez Canillas In-Reply-To: <20221012142707.GD28810@kitsune.suse.cz> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-fbdev@vger.kernel.org Hello, On 10/12/22 16:27, Michal Suchánek wrote: [...] >> >> If you are using the framebuffer code from vga.c, I would guess that >> that you can run a big-endian kernel with qemu-system-ppc64, >> or a little-endian kernel with qemu-system-ppc64le and get the >> correct colors, while running a little-endian kernel with >> qemu-system-ppc64 and vga.c, or using a different framebuffer >> emulation on a big-endian kernel would give you the wrong colors. > > Thanks for digging this up. > > That makes one thing clear: qemu does not emulate this framebuffer > property correctly, and cannot be relied on for verification. > > If you can provide test results from real hardware that show the current > logic as flawed it should be changed. > > In absence of such test results I think the most reasonable thing is to > keep the logic that nobody complained about for 10+ years. > I agree with Michal and Thomas on this. I don't see a strong reason to not use the same heuristic that the offb fbdev driver has been doing for this. Otherwise if this turns out to be needed, it will cause a regression for a user that switches to this driver instead. Specially since both fbdev and DRM drivers match against the same "display" OF compatible string. -- Best regards, Javier Martinez Canillas Core Platforms Red Hat