On 6/16/26 3:21 AM, Rodrigo Alencar via B4 Relay wrote:
> From: Rodrigo Alencar <[email protected]>
>
> Use of local SPI bus data to manage a collection of SPI transfers and
> flush them to the SPI platform driver with the sync() operation. This
> allows for faster handling of multiple channel DAC writes, avoiding kernel
> overhead per spi_sync() call, which will be helpful when enabling
> triggered buffer support.
>
> Signed-off-by: Rodrigo Alencar <[email protected]>
> ---
> drivers/iio/dac/ad5686-spi.c | 121
> ++++++++++++++++++++++++++++++++-----------
> drivers/iio/dac/ad5686.c | 4 +-
> drivers/iio/dac/ad5686.h | 8 ++-
> drivers/iio/dac/ad5696-i2c.c | 2 +-
> 4 files changed, 100 insertions(+), 35 deletions(-)
>
> diff --git a/drivers/iio/dac/ad5686-spi.c b/drivers/iio/dac/ad5686-spi.c
> index 6b6ef1d7071f..77c86674d178 100644
> --- a/drivers/iio/dac/ad5686-spi.c
> +++ b/drivers/iio/dac/ad5686-spi.c
> @@ -12,59 +12,91 @@
> #include <linux/errno.h>
> #include <linux/mod_devicetable.h>
> #include <linux/module.h>
> +#include <linux/overflow.h>
> #include <linux/spi/spi.h>
>
> #include <asm/byteorder.h>
>
> #include "ad5686.h"
>
> +/**
> + * struct ad5686_spi_data - SPI bus specific data
> + * @msg: SPI message used for transfers
> + * @size: number of transfers currently in the message
> + * @capacity: maximum number of transfers that can be added to the message
> + * @xfers: array of SPI transfers, allocated with the provided capacity
> + */
> +struct ad5686_spi_data {
> + struct spi_message msg;
> + unsigned int size;
> + unsigned int capacity;
> + struct spi_transfer xfers[] __counted_by(capacity);
> +};
> +
> static int ad5686_spi_write(struct ad5686_state *st,
> u8 cmd, u8 addr, u16 val)
> {
> - struct spi_device *spi = to_spi_device(st->dev);
> - u8 tx_len, *buf;
> + struct ad5686_spi_data *bus_data = st->bus_data;
> + struct spi_transfer *xfer;
>
> + if (bus_data->size >= bus_data->capacity)
> + return -E2BIG;
> +
> + if (bus_data->size)
> + bus_data->xfers[bus_data->size - 1].cs_change = 1;
> + else
> + spi_message_init(&bus_data->msg);
Seems odd that spi_message_init() is called conditionally. What
prevents spi_message_add_tail() from growing the message unbounded
on repeated calls?
> +
> + xfer = &bus_data->xfers[bus_data->size];
> switch (st->chip_info->regmap_type) {
> case AD5310_REGMAP:
> - st->data[0].d16 = cpu_to_be16(AD5310_CMD(cmd) |
> - val);
> - buf = &st->data[0].d8[0];
> - tx_len = 2;
> + st->data[bus_data->size].d16 =
> + cpu_to_be16(AD5310_CMD(cmd) | val);
> + *xfer = (struct spi_transfer) {
> + .tx_buf = &st->data[bus_data->size].d16,
> + .len = sizeof(st->data[bus_data->size].d16),
> + };
> break;
> case AD5683_REGMAP:
> - st->data[0].d32 = cpu_to_be32(AD5686_CMD(cmd) |
> - AD5683_DATA(val));
> - buf = &st->data[0].d8[1];
> - tx_len = 3;
> + st->data[bus_data->size].d32 =
> + cpu_to_be32(AD5686_CMD(cmd) | AD5683_DATA(val));
> + *xfer = (struct spi_transfer) {
> + .tx_buf = &st->data[bus_data->size].d8[1],
> + .len = sizeof(st->data[bus_data->size].d32) - 1,
> + };
> break;
> case AD5686_REGMAP:
> - st->data[0].d32 = cpu_to_be32(AD5686_CMD(cmd) |
> - AD5686_ADDR(addr) |
> - val);
> - buf = &st->data[0].d8[1];
> - tx_len = 3;
> + st->data[bus_data->size].d32 =
> + cpu_to_be32(AD5686_CMD(cmd) | AD5686_ADDR(addr) | val);
> + *xfer = (struct spi_transfer) {
> + .tx_buf = &st->data[bus_data->size].d8[1],
> + .len = sizeof(st->data[bus_data->size].d32) - 1,
> + };
> break;
> default:
> return -EINVAL;
> }
>
> - return spi_write(spi, buf, tx_len);
If this function no longer writes, should we change the name of
the function to something like ad5686_spi_write_prepare_msg()?
> + spi_message_add_tail(xfer, &bus_data->msg);
> + bus_data->size++;
> +
> + return 0;
> +}
> +
> +static int ad5686_spi_sync(struct ad5686_state *st)
> +{
> + struct spi_device *spi = to_spi_device(st->dev);
> + struct ad5686_spi_data *bus_data = st->bus_data;
> +
> + bus_data->size = 0; /* always reset, even on sync failure */
> + return spi_sync(spi, &bus_data->msg);
> }
>
> static int ad5686_spi_read(struct ad5686_state *st, u8 addr)
> {
> - struct spi_transfer t[] = {
> - {
> - .tx_buf = &st->data[0].d8[1],
> - .len = 3,
> - .cs_change = 1,
> - }, {
> - .tx_buf = &st->data[1].d8[1],
> - .rx_buf = &st->data[2].d8[1],
> - .len = 3,
> - },
> - };
> struct spi_device *spi = to_spi_device(st->dev);
> + struct ad5686_spi_data *bus_data = st->bus_data;
> + struct spi_transfer *xfer = &bus_data->xfers[0];
> u8 cmd = 0;
> int ret;
>
> @@ -85,8 +117,21 @@ static int ad5686_spi_read(struct ad5686_state *st, u8
> addr)
> AD5686_ADDR(addr));
> st->data[1].d32 = cpu_to_be32(AD5686_CMD(AD5686_CMD_NOOP));
>
> - ret = spi_sync_transfer(spi, t, ARRAY_SIZE(t));
> - if (ret < 0)
> + xfer[0] = (struct spi_transfer) {
> + .tx_buf = &st->data[0].d8[1],
> + .len = sizeof(st->data[0].d32) - 1,
Would make more sense to say `sizeof(st->data[0].d8) - 1` since
the buffer is &st->data[0].d8[1].
> + .cs_change = 1,
> + };
> + xfer[1] = (struct spi_transfer) {
> + .tx_buf = &st->data[1].d8[1],
> + .rx_buf = &st->data[2].d8[1],
> + .len = sizeof(st->data[1].d32) - 1,
And here.
> + };
> +
> + spi_message_init_with_transfers(&bus_data->msg, xfer, 2);
> +
> + ret = spi_sync(spi, &bus_data->msg);
> + if (ret)
> return ret;
>
> return be32_to_cpu(st->data[2].d32);
> @@ -95,12 +140,26 @@ static int ad5686_spi_read(struct ad5686_state *st, u8
> addr)
> static const struct ad5686_bus_ops ad5686_spi_ops = {
> .write = ad5686_spi_write,
> .read = ad5686_spi_read,
> + .sync = ad5686_spi_sync,
> };
>
