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Tue, 14 Oct 2025 15:03:06 -0700 (PDT) From: David Lechner Date: Tue, 14 Oct 2025 17:02:13 -0500 Subject: [PATCH 3/6] spi: add multi_bus_mode field to struct spi_transfer Precedence: bulk X-Mailing-List: devicetree@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Message-Id: <20251014-spi-add-multi-bus-support-v1-3-2098c12d6f5f@baylibre.com> References: <20251014-spi-add-multi-bus-support-v1-0-2098c12d6f5f@baylibre.com> In-Reply-To: <20251014-spi-add-multi-bus-support-v1-0-2098c12d6f5f@baylibre.com> To: Mark Brown , Rob Herring , Krzysztof Kozlowski , Conor Dooley , Marcelo Schmitt , Michael Hennerich , =?utf-8?q?Nuno_S=C3=A1?= , Jonathan Cameron , Andy Shevchenko Cc: Sean Anderson , linux-spi@vger.kernel.org, devicetree@vger.kernel.org, linux-kernel@vger.kernel.org, linux-iio@vger.kernel.org, David Lechner X-Mailer: b4 0.14.2 X-Developer-Signature: v=1; a=openpgp-sha256; l=3744; i=dlechner@baylibre.com; h=from:subject:message-id; bh=4CqVCZcygZWUEZQ30wthncfqjOostuEs/o8pgXKJiB0=; b=owEBbQGS/pANAwAKAcLMIAH/AY/AAcsmYgBo7sh6BzPQljNleuRvHGy1T+//g8qgNkkcKEB7m t2x2s/6pxuJATMEAAEKAB0WIQTsGNmeYg6D1pzYaJjCzCAB/wGPwAUCaO7IegAKCRDCzCAB/wGP wFtUB/9dBUXIQU9ybm7B92Fho2l86h72tDmoH2+mQWM06nRRo13tlDzZ3P60vvjI70TPS5wwUCC WNwyJTo5eVpAAh9+TIlXegk+8sC77xSUAc7vmKCgfKn7vamIiXizC5cEfFXXrv0WBHPcsMz5UMQ 9T735QHdr+wEau9l4S9YdycINg726ZCdjm2WECdnvKKK+2P70NMPi3gJVQ3/KHY+27+BaXCKA/K maJwkWwxR6xLywlPtD9s+yBJ1ZUapklb4KXKHq9anZxuAfmEFqOmq4g21HYfpVZapESx4DUMyIu LgBST6h8Td9uHSqHE3Hv1i8OWJkGRttY+iXO2N5IXm7c4ZFG X-Developer-Key: i=dlechner@baylibre.com; a=openpgp; fpr=8A73D82A6A1F509907F373881F8AF88C82F77C03 Add a new multi_bus_mode field to struct spi_transfer to allow peripherals that support multiple SPI buses to be used with a single SPI controller. This requires both the peripheral and the controller to have multiple serializers connected to separate data buses. It could also be used with a single controller and multiple peripherals that are functioning as a single logical device (similar to parallel memories). The possible values for this field have the following semantics: - SPI_MULTI_BUS_MODE_SINGLE: Only use the first bus. This means that it it is operating just like a conventional SPI bus. It is the default value so that existing drivers do not need to be modified. Example: tx_buf[0] = 0x88; struct spi_transfer xfer = { .tx_buf = tx_buf, .len = 1, }; spi_sync_transfer(spi, &xfer, 1); controller > data bits > peripheral ---------- ---------------- ---------- SDO 0 0-0-0-1-0-0-0-1 SDI 0 - SPI_MULTI_BUS_MODE_MIRROR: Send a single data word over all of the buses at the same time. This only makes sense for writes and not for reads. Example: tx_buf[0] = 0x88; struct spi_transfer xfer = { .tx_buf = tx_buf, .len = 1, .multi_bus_mode = SPI_MULTI_BUS_MODE_MIRROR, }; spi_sync_transfer(spi, &xfer, 1); controller > data bits > peripheral ---------- ---------------- ---------- SDO 0 0-0-0-1-0-0-0-1 SDI 0 SDO 1 0-0-0-1-0-0-0-1 SDI 1 - SPI_MULTI_BUS_MODE_STRIPE: Send or receive two different data words at the same time, one on each bus. Example: struct spi_transfer xfer = { .rx_buf = rx_buf, .len = 2, /* must be multiple of number of buses */ .multi_bus_mode = SPI_MULTI_BUS_MODE_STRIPE, }; spi_sync_transfer(spi, &xfer, 1); controller < data bits < peripheral ---------- ---------------- ---------- SDI 0 0-0-0-1-0-0-0-1 SDO 0 SDI 1 1-0-0-0-1-0-0-0 SDO 1 After the transfer, rx_buf[0] == 0x11 (word from SDO 0) and rx_buf[1] == 0x88 (word from SDO 1). If the transfer was longer, the data would continue in an alternating fashion. Signed-off-by: David Lechner --- include/linux/spi/spi.h | 6 ++++++ 1 file changed, 6 insertions(+) diff --git a/include/linux/spi/spi.h b/include/linux/spi/spi.h index c314194d4e7e2b396795ece10e142118ca05f4eb..7d22ef5077d1229cac2574831f80092c591b972f 100644 --- a/include/linux/spi/spi.h +++ b/include/linux/spi/spi.h @@ -976,6 +976,8 @@ struct spi_res { * (SPI_NBITS_SINGLE) is used. * @rx_nbits: number of bits used for reading. If 0 the default * (SPI_NBITS_SINGLE) is used. + * @multi_bus_mode: How to serialize data on multiple buses. One of the + * SPI_MULTI_BUS_MODE_* values. * @len: size of rx and tx buffers (in bytes) * @speed_hz: Select a speed other than the device default for this * transfer. If 0 the default (from @spi_device) is used. @@ -1112,6 +1114,10 @@ struct spi_transfer { unsigned cs_change:1; unsigned tx_nbits:4; unsigned rx_nbits:4; + unsigned multi_bus_mode: 2; +#define SPI_MULTI_BUS_MODE_SINGLE 0 /* only use single bus */ +#define SPI_MULTI_BUS_MODE_STRIPE 1 /* one data word per bus */ +#define SPI_MULTI_BUS_MODE_MIRROR 2 /* same word sent on all buses */ unsigned timestamped:1; bool dtr_mode; #define SPI_NBITS_SINGLE 0x01 /* 1-bit transfer */ -- 2.43.0