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Feedback-ID: i56a14606:Fastmail Received: by mailuser.nyi.internal (Postfix, from userid 501) id 97747B60086; Tue, 11 Oct 2022 16:07:30 -0400 (EDT) X-Mailer: MessagingEngine.com Webmail Interface User-Agent: Cyrus-JMAP/3.7.0-alpha0-1047-g9e4af4ada4-fm-20221005.001-g9e4af4ad Mime-Version: 1.0 Message-Id: <9162f41f-28c3-493c-ab54-b1c4a2fdf494@app.fastmail.com> In-Reply-To: <83071743-a7f2-f761-baa3-da688f26b5e3@suse.de> References: <20220928105010.18880-1-tzimmermann@suse.de> <20220928105010.18880-6-tzimmermann@suse.de> <23333ff7-3ae1-494f-7abe-62da6698fd00@redhat.com> <83071743-a7f2-f761-baa3-da688f26b5e3@suse.de> Date: Tue, 11 Oct 2022 22:06:59 +0200 From: "Arnd Bergmann" To: "Thomas Zimmermann" , "Javier Martinez Canillas" , "David Airlie" , "Daniel Vetter" , "Helge Deller" , maxime@cerno.tech, sam@ravnborg.org, "Michal Suchanek" , "Michael Ellerman" , benh@kernel.crashing.org, "Paul Mackerras" , "Geert Uytterhoeven" , mark.cave-ayland@ilande.co.uk Subject: Re: [PATCH v4 5/5] drm/ofdrm: Support big-endian scanout buffers Content-Type: text/plain X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: linux-fbdev@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, dri-devel@lists.freedesktop.org Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" On Tue, Oct 11, 2022, at 1:30 PM, Thomas Zimmermann wrote: > Am 11.10.22 um 09:46 schrieb Javier Martinez Canillas: >>> +static bool display_get_big_endian_of(struct drm_device *dev, struct device_node *of_node) >>> +{ >>> + bool big_endian; >>> + >>> +#ifdef __BIG_ENDIAN >>> + big_endian = true; >>> + if (of_get_property(of_node, "little-endian", NULL)) >>> + big_endian = false; >>> +#else >>> + big_endian = false; >>> + if (of_get_property(of_node, "big-endian", NULL)) >>> + big_endian = true; >>> +#endif >>> + >>> + return big_endian; >>> +} >>> + >> >> Ah, I see. The heuristic then is whether the build is BE or LE or if the Device >> Tree has an explicit node defining the endianess. The patch looks good to me: > > Yes. I took this test from offb. Has the driver been tested with little-endian kernels though? While ppc32 kernels are always BE, you can build kernels as either big-endian or little-endian for most (modern) powerpc64 and arm/arm64 hardware, and I don't see why that should change the defaults of the driver when describing the same framebuffer hardware. I could understand having a default to e.g. big-endian on all powerpc and a default for little-endian on all arm, but having it tied to the way the kernel is built seems wrong, and doesn't make sense in a DT binding either. Arnd