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[108.51.35.162]) by smtp.googlemail.com with ESMTPSA id j50sm6081221qtc.5.2020.11.09.05.47.11 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 09 Nov 2020 05:47:11 -0800 (PST) Subject: Re: [PATCH 03/32] spi: dw: Fix driving MOSI low while recieving To: Mark Brown , Damien Le Moal References: <20201107081420.60325-1-damien.lemoal@wdc.com> <20201107081420.60325-4-damien.lemoal@wdc.com> <20201109132935.GB6380@sirena.org.uk> From: Sean Anderson Autocrypt: addr=seanga2@gmail.com; prefer-encrypt=mutual; keydata= mQENBFe74PkBCACoLC5Zq2gwrDcCkr+EPGsT14bsxrW07GiYzQhLCgwnPdEpgU95pXltbFhw 46GfyffABWxHKO2x+3L1S6ZxC5AiKbYXo7lpnTBYjamPWYouz+VJEVjUx9aaSEByBah5kX6a lKFZWNbXLAJh+dE1HFaMi3TQXXaInaREc+aO1F7fCa2zNE75ja+6ah8L4TPRFZ2HKQzve0/Y GXtoRw97qmnm3U36vKWT/m2AiLF619F4T1mHvlfjyd9hrVwjH5h/2rFyroXVXBZHGA9Aj8eN F2si35dWSZlIwXkNu9bXp0/pIu6FD0bI+BEkD5S7aH1G1iAcMFi5Qq2RNa041DfQSDDHABEB AAG0K1NlYW4gR2FsbGFnaGVyIEFuZGVyc29uIDxzZWFuZ2EyQGdtYWlsLmNvbT6JAVcEEwEK AEECGwMFCwkIBwIGFQgJCgsCBBYCAwECHgECF4ACGQEWIQSQYR1bzo1I0gPoYCg+6I/stKEQ bgUCXT+S2AUJB2TlXwAKCRA+6I/stKEQbhNOB/9ooea0hU9Sgh7PBloU6CgaC5mlqPLB7NTp +JkB+nh3Fqhk+qLZwzEynnuDLl6ESpVHIc0Ym1lyF4gT3DsrlGT1h0Gzw7vUwd1+ZfN0CuIx Rn861U/dAUjvbtN5kMBqOI4/5ea+0r7MACcIVnKF/wMXBD8eypHsorT2sJTzwZ6DRCNP70C5 N1ahpqqNmXe0uLdP0pu55JCqhrGw2SinkRMdWyhSxT56uNwIVHGhLTqH7Q4t1N6G1EH626qa SvIJsWlNpll6Y3AYLDw2/Spw/hqieS2PQ/Ky3rPZnvJt7/aSNYsKoFGX0yjkH67Uq8Lx0k1L w8jpXnbEPQN3A2ZJCbeM Message-ID: Date: Mon, 9 Nov 2020 08:47:10 -0500 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.12.0 MIME-Version: 1.0 In-Reply-To: <20201109132935.GB6380@sirena.org.uk> Content-Language: en-US X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20201109_084715_861353_A9DFBBE0 X-CRM114-Status: GOOD ( 23.05 ) X-BeenThere: linux-riscv@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: devicetree@vger.kernel.org, Stephen Boyd , Linus Walleij , Serge Semin , linux-spi@vger.kernel.org, linux-gpio@vger.kernel.org, Rob Herring , Palmer Dabbelt , Philipp Zabel , linux-riscv@lists.infradead.org, Frank Rowand , linux-clk@vger.kernel.org Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-riscv" Errors-To: linux-riscv-bounces+linux-riscv=archiver.kernel.org@lists.infradead.org On 11/9/20 8:29 AM, Mark Brown wrote: > On Sat, Nov 07, 2020 at 05:13:51PM +0900, Damien Le Moal wrote: > >> The resting state of MOSI is high when nothing is driving it. If we >> drive it low while recieving, it looks like we are transmitting 0x00 >> instead of transmitting nothing. This can confuse slaves (like SD cards) >> which allow new commands to be sent over MOSI while they are returning >> data over MISO. The return of MOSI from 0 to 1 at the end of recieving >> a byte can look like a start bit and a transmission bit to an SD card. > > If client devices are interpreting the transmitted data then I would > expect the drivers for that hardware to be ensuring that whatever we > transmit matches what the device is expecting. We shouldn't be putting > a hack in a particular controller driver to paper over things, that will > mean that the device will break when used with other controllers and if > different devices have different requirements then obviously we can't > satisfy them. There is not meaningfully a general specification for SPI > which says what happens when signals are idle, it's all specific to the > client device. > > In this case it also looks like the controller hardware requires > transmit data and therefore should be setting SPI_MUST_TX and just > removing the in driver default anyway, though that will have no effect > one way or anther on the issue you're seeing. There is a recieve-only mode, but it is not used by this driver. Perhaps it should be. > Please also try to avoid the use of master/slave terminology where > reasonable, controller and device tend to work for SPI (though MOSI/MISO > are going to be harder to shift). Here I use it to draw distinction between the SPI master and the SPI slave, which are both devices in different contexts. --Sean _______________________________________________ linux-riscv mailing list linux-riscv@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-riscv