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[192.26.37.52]) by smtp.gmail.com with ESMTPSA id be2sm12745741edb.92.2020.07.03.07.13.46 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 03 Jul 2020 07:13:47 -0700 (PDT) From: Adrian Fiergolski Cc: geert@linux-m68k.org, lukas@wunner.de, Adrian Fiergolski , Mark Brown , Rob Herring , linux-spi@vger.kernel.org, devicetree@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [PATCH 2/2] dt-bindings: Add documentation for SPI daisy chain driver. Date: Fri, 3 Jul 2020 16:12:44 +0200 Message-Id: <20200703141246.17281-2-adrian.fiergolski@fastree3d.com> X-Mailer: git-send-email 2.27.0 In-Reply-To: <20200703141246.17281-1-adrian.fiergolski@fastree3d.com> References: <20200703141246.17281-1-adrian.fiergolski@fastree3d.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit To: unlisted-recipients:; (no To-header on input) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Add documentation for SPI daisy chain driver. Signed-off-by: Adrian Fiergolski --- .../bindings/spi/spi-daisy_chain.txt | 56 +++++++++++++++++++ 1 file changed, 56 insertions(+) create mode 100644 Documentation/devicetree/bindings/spi/spi-daisy_chain.txt diff --git a/Documentation/devicetree/bindings/spi/spi-daisy_chain.txt b/Documentation/devicetree/bindings/spi/spi-daisy_chain.txt new file mode 100644 index 000000000000..1e5b046dda83 --- /dev/null +++ b/Documentation/devicetree/bindings/spi/spi-daisy_chain.txt @@ -0,0 +1,56 @@ +spi-daisy_chain : The driver handling SPI daisy chains. +----------------------------------------------------------- + +Required properties: +- compatible : Should be "spi,daisy_chain" +- reg : Chip select assigned to the chain + + For the SPI devices on a common SPI chain - nodes of daisy_chain): +- spi-daisy-chain-len : Length (in bytes) of the SPI transfer, + when the SPI device is part of a device chain. +- spi-daisy-chain-noop : Byte string of no-operation command which should + be send when device is not addressed during the + given SPI transfer + +Optional properties: + (for the SPI devices on a common SPI chain (nodes of daisy_chain): +- spi-daisy-chain-bits_per_word : no-operation transfers involve + one or more words; word sizes like + eight or 12 bits are common. + In-memory wordsizes are powers of two + bytes (e.g. 20 bit samples use 32 bits). + If not defined, it is assumed to be 8. + +The daisy chain is a virtual device represented as a regular SPI device. Its +nodes define physical devices available on the chain. The order of the nodes +defines the order of the physical devices on the chain: MOSI pin of a device +represented by the first node is the last one on the MOSI daisy chain. The +daisy-chain functionality is transparent to the drivers of the physical devices +on the chain. All nodes share SPI mode, chip select and a max speed of the +virtual daisy chain device. Once one of the physical devices is being accessed, +the spi-daisy_chain driver combines this data with no-operation commands of all +other devices on the chain. + +Example: + + daisy_chain0: daisy_chain@0 { + compatible = "spi,daisy_chain"; + spi-max-frequency = <10000000>; + reg = <0>; + + dac0: ltc2632@0 { + compatible = "lltc,ltc2634-l12"; + spi-daisy-chain-len = <4>; + spi-daisy-chain-noop = [00 F0 00 00]; + }; + dac1: ltc2632@1 { + compatible = "lltc,ltc2634-l12"; + spi-daisy-chain-len = <4>; + spi-daisy-chain-noop = [00 F0 00 00]; + }; + dac2: ltc2632@2 { + compatible = "lltc,ltc2634-l12"; + spi-daisy-chain-len = <4>; + spi-daisy-chain-noop = [00 F0 00 00]; + }; + }; -- 2.27.0