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([2a0e:41a:894f:0:6f8e:6bf6:725c:d7d5]) by smtp.gmail.com with ESMTPSA id u16-20020a05600c19d000b003cf37c5ddc0sm5775361wmq.22.2022.11.18.11.02.33 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 18 Nov 2022 11:02:33 -0800 (PST) From: Carlo Caione X-Google-Original-From: Carlo Caione Message-ID: <8a3bdd84-2789-1b42-976f-2843320750b6@baylibre.com> Date: Fri, 18 Nov 2022 20:02:32 +0100 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.4.2 Subject: Re: [PATCH 2/3] drm/tiny: ili9486: Do not assume 8-bit only SPI controllers Content-Language: en-US To: Mark Brown Cc: Kamlesh Gurudasani , Neil Armstrong , Jerome Brunet , David Airlie , Martin Blumenstingl , Kevin Hilman , Daniel Vetter , linux-arm-kernel@lists.infradead.org, linux-amlogic@lists.infradead.org, linux-kernel@vger.kernel.org, linux-spi@vger.kernel.org, dri-devel@lists.freedesktop.org References: <20221116-s905x_spi_ili9486-v1-0-630401cb62d5@baylibre.com> <20221116-s905x_spi_ili9486-v1-2-630401cb62d5@baylibre.com> In-Reply-To: X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20221118_110243_749379_A4E3448D X-CRM114-Status: UNSURE ( 9.76 ) X-CRM114-Notice: Please train this message. X-BeenThere: linux-amlogic@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset="us-ascii"; Format="flowed" Sender: "linux-amlogic" Errors-To: linux-amlogic-bounces+linux-amlogic=archiver.kernel.org@lists.infradead.org On 18/11/2022 16:44, Mark Brown wrote: >> The problem arrives when your controller does support 16-bits, so >> your data is not swapped, but you still put the data on the bus >> with 8-bit transfers. > > Why would you need to use 8 bit transfers if the controller supports > 16 bits? No idea why this driver is forcing 8-bit transfers when the controller supports 16-bits (this is what this patch is fixing). My theory is that this driver was written with the Raspberry Pi HATs in mind and (AFAICT) the RPi has an 8-bit only SPI controller so the driver author didn't bother with anything different. -- Carlo Caione _______________________________________________ linux-amlogic mailing list linux-amlogic@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-amlogic