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Fri, 07 Nov 2025 12:53:46 -0800 (PST) From: David Lechner Date: Fri, 07 Nov 2025 14:52:49 -0600 Subject: [PATCH v2 3/6] spi: add multi_bus_mode field to struct spi_transfer Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable Message-Id: <20251107-spi-add-multi-bus-support-v2-3-8a92693314d9@baylibre.com> References: <20251107-spi-add-multi-bus-support-v2-0-8a92693314d9@baylibre.com> In-Reply-To: <20251107-spi-add-multi-bus-support-v2-0-8a92693314d9@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=3841; i=dlechner@baylibre.com; h=from:subject:message-id; bh=uBZhRBQvKxN5Rbc+PdSnTkkrZAa+WeV1PheO2s8Yfj0=; b=owEBbQGS/pANAwAKAcLMIAH/AY/AAcsmYgBpDlw6WL09bq9iy+/GN33p/vb2QS8/tlJSTsR8H F4YmjIugkKJATMEAAEKAB0WIQTsGNmeYg6D1pzYaJjCzCAB/wGPwAUCaQ5cOgAKCRDCzCAB/wGP wC8VB/4wshs9FzXaveEoEjEhM+PG0nDRH0fQV4ZScm5cEAV+PAJPkqnMUu+GvtyQo1Qe5OLjZcR rjJfhnozvGJ7I91mbnuVX6fXsJ8EbX+faFEJbSjEyLGtzsolg5Zhwbws8KKRDqEAC4Z4fIO8l/7 bwTVB4QbJqfYpYoAXGRS/HZ+KjFd3k5qBmC+B2G4h5Z4i1ux+qMF0otPmcksaPQMsHmZDRNFeWY TghgoBn+sobC+tXMSawtC4sKeBHToHRJwExDy/Y/0+araYcGqzQeynLrv/4d0NcEliRIS1CpP+T XDZxb1cv9dEKZok/p9EyooZrSDMqnK0atHgj4p5IUI+m8T48 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] =3D 0x88; struct spi_transfer xfer =3D { .tx_buf =3D tx_buf, .len =3D 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] =3D 0x88; struct spi_transfer xfer =3D { .tx_buf =3D tx_buf, .len =3D 1, .multi_bus_mode =3D 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 =3D { .rx_buf =3D rx_buf, .len =3D 2, /* must be multiple of number of buses */ .multi_bus_mode =3D 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] =3D=3D 0x11 (word from SDO 0) and rx_buf[1] =3D=3D 0x88 (word from SDO 1). If the transfer was longer, the data would continue in an alternating fashion. Acked-by: Nuno S=C3=A1 Acked-by: Marcelo Schmitt 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..7d22ef5077d1229cac2574831f8= 0092c591b972f 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 */ --=20 2.43.0