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Nikolaus Schaller" In-Reply-To: <13356060.GkHXLIg068@jason> Date: Wed, 19 Jan 2022 07:40:22 +0100 Cc: Paul Cercueil , Mark Rutland , Geert Uytterhoeven , Neil Armstrong , David Airlie , dri-devel , linux-mips , Andrzej Hajda , Laurent Pinchart , Miquel Raynal , Sam Ravnborg , Jernej Skrabec , Harry Wentland , OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS , Kees Cook , Jonas Karlman , Mark Brown , Maxime Ripard , Thomas Bogendoerfer , Liam Girdwood , Robert Foss , linux-kernel , Rob Herring , Daniel Vetter , Hans Verkuil , Discussions about the Letux Kernel Content-Transfer-Encoding: quoted-printable Message-Id: References: <13356060.GkHXLIg068@jason> To: Paul Boddie X-Mailer: Apple Mail (2.3445.104.21) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Paul, > Am 18.01.2022 um 23:59 schrieb Paul Boddie : >=20 > On Tuesday, 18 January 2022 17:58:58 CET Paul Cercueil wrote: >>=20 >> Not at all. If the clock is disabled, the LCD controller is disabled, >> so all the registers read zero, this makes sense. You can only read = the >> registers when the clock is enabled. On some SoCs, reading disabled >> registers can even cause a complete lockup. >=20 > My concern was that something might be accessing the registers before = the=20 > clock had been enabled. It seems unlikely, given that the clock is = enabled in=20 > the bind function, and I would have thought that nothing would invoke = the=20 > different driver operations ("funcs") until bind has been called, nor = should=20 > anything called from within bind itself be accessing registers. >=20 >> Why is this JZ_LCD_OSDC_ALPHAEN bit needed now? I remember it working >> fine last time I tried, and now I indeed get a black screen unless = this >> bit is set. The PM doesn't make it obvious that the bit is required, >> but that wouldn't be surprising. >=20 > It isn't actually needed. If the DMA descriptors are set up = appropriately, the=20 > OSD alpha bit seems to be set as a consequence. In my non-Linux = testing=20 > environment I don't even set any OSD registers explicitly, but the OSD = alpha=20 > and enable flags become set when the display is active. Is it set by DMA descriptors or by explicit code? We did have an explicit setting of JZ_LCD_OSDC_ALPHAEN https://www.spinics.net/lists/devicetree/msg438447.html but that was postponed for further discussion. And now if we add it (from basic functionality) back, it is fine again. BR, Nikolaus=