On Wed, 5 Apr 2023, Jan Kundrát wrote:
> After upgrading from 5.16 to 6.1, our board with a MAX14830 started
> producing lots of garbage data over UART. Bisection pointed out commit
> 285e76fc049c as the culprit. That patch tried to replace hand-written
> code which I added in 2b4bac48c1084 ("serial: max310x: Use batched reads
> when reasonably safe") with the generic regmap infrastructure for
> batched operations.
>
> Unfortunately, the `regmap_raw_read` and `regmap_raw_write` which were
> used are actually functions which perform IO over *multiple* registers.
> That's not what is needed for accessing these Tx/Rx FIFOs; the
> appropriate functions are the `_noinc_` versions, not the `_raw_` ones.
>
> Fix this regression by using `regmap_noinc_read()` and
> `regmap_noinc_write()` along with the necessary `regmap_config` setup;
> with this patch in place, our board communicates happily again. Since
> our board uses SPI for talking to this chip, the I2C part is completely
> untested.
>
> Fixes: 285e76fc049c serial: max310x: use regmap methods for SPI batch operations
> Signed-off-by: Jan Kundrát <jan.kundrat@xxxxxxxxx>
> Cc: stable@xxxxxxxxxxxxxxx
> ---
> drivers/tty/serial/max310x.c | 17 +++++++++++++++--
> 1 file changed, 15 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/tty/serial/max310x.c b/drivers/tty/serial/max310x.c
> index c82391c928cb..47520d4a381f 100644
> --- a/drivers/tty/serial/max310x.c
> +++ b/drivers/tty/serial/max310x.c
> @@ -529,6 +529,11 @@ static bool max310x_reg_precious(struct device *dev, unsigned int reg)
> return false;
> }
>
> +static bool max310x_reg_noinc(struct device *dev, unsigned int reg)
> +{
> + return reg == MAX310X_RHR_REG;
I'd either add a comment or just do || reg == MAX310X_THR_REG (which
probably gets optimized away by the compiler) to make it look less magic
for the Tx side.
--
i.
> +}
> +
> static int max310x_set_baud(struct uart_port *port, int baud)
> {
> unsigned int mode = 0, div = 0, frac = 0, c = 0, F = 0;
> @@ -658,14 +663,14 @@ static void max310x_batch_write(struct uart_port *port, u8 *txbuf, unsigned int
> {
> struct max310x_one *one = to_max310x_port(port);
>
> - regmap_raw_write(one->regmap, MAX310X_THR_REG, txbuf, len);
> + regmap_noinc_write(one->regmap, MAX310X_THR_REG, txbuf, len);
> }
>
> static void max310x_batch_read(struct uart_port *port, u8 *rxbuf, unsigned int len)
> {
> struct max310x_one *one = to_max310x_port(port);
>
> - regmap_raw_read(one->regmap, MAX310X_RHR_REG, rxbuf, len);
> + regmap_noinc_read(one->regmap, MAX310X_RHR_REG, rxbuf, len);
> }
>
> static void max310x_handle_rx(struct uart_port *port, unsigned int rxlen)
> @@ -1480,6 +1485,10 @@ static struct regmap_config regcfg = {
> .writeable_reg = max310x_reg_writeable,
> .volatile_reg = max310x_reg_volatile,
> .precious_reg = max310x_reg_precious,
> + .writeable_noinc_reg = max310x_reg_noinc,
> + .readable_noinc_reg = max310x_reg_noinc,
> + .max_raw_read = MAX310X_FIFO_SIZE,
> + .max_raw_write = MAX310X_FIFO_SIZE,
> };
>
> #ifdef CONFIG_SPI_MASTER
> @@ -1565,6 +1574,10 @@ static struct regmap_config regcfg_i2c = {
> .volatile_reg = max310x_reg_volatile,
> .precious_reg = max310x_reg_precious,
> .max_register = MAX310X_I2C_REVID_EXTREG,
> + .writeable_noinc_reg = max310x_reg_noinc,
> + .readable_noinc_reg = max310x_reg_noinc,
> + .max_raw_read = MAX310X_FIFO_SIZE,
> + .max_raw_write = MAX310X_FIFO_SIZE,
> };
>
> static const struct max310x_if_cfg max310x_i2c_if_cfg = {
>
