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SubjectRe: [PATCH] spi: fsl_spi: Don't change speed while chipselect is active
Hi Christophe,

On Wed, 14 Dec 2022 14:41:33 +0100
Christophe Leroy <christophe.leroy@csgroup.eu> wrote:

> Commit c9bfcb315104 ("spi_mpc83xx: much improved driver") made
> modifications to the driver to not perform speed changes while
> chipselect is active. But those changes where lost with the
> convertion to tranfer_one.
>
> Previous implementation was allowing speed changes during
> message transfer when cs_change flag was set.
> At the time being, core SPI does not provide any feature to change
> speed while chipselect is off, so do not allow any speed change during
> message transfer, and perform the transfer setup in prepare_message
> in order to set correct speed while chipselect is still off.
>
> Reported-by: Herve Codina <herve.codina@bootlin.com>
> Fixes: 64ca1a034f00 ("spi: fsl_spi: Convert to transfer_one")
> Cc: stable@vger.kernel.org
> Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
> Tested-by: Herve Codina <herve.codina@bootlin.com>
> ---
> drivers/spi/spi-fsl-spi.c | 19 ++++++++++++++++---
> 1 file changed, 16 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/spi/spi-fsl-spi.c b/drivers/spi/spi-fsl-spi.c
> index 731624f157fc..93152144fd2e 100644
> --- a/drivers/spi/spi-fsl-spi.c
> +++ b/drivers/spi/spi-fsl-spi.c
> @@ -333,13 +333,26 @@ static int fsl_spi_prepare_message(struct spi_controller *ctlr,
> {
> struct mpc8xxx_spi *mpc8xxx_spi = spi_controller_get_devdata(ctlr);
> struct spi_transfer *t;
> + struct spi_transfer *first;
> +
> + first = list_first_entry(&m->transfers, struct spi_transfer,
> + transfer_list);
>
> /*
> * In CPU mode, optimize large byte transfers to use larger
> * bits_per_word values to reduce number of interrupts taken.
> + *
> + * Some glitches can appear on the SPI clock when the mode changes.
> + * Check that there is no speed change during the transfer and set it up
> + * now to change the mode without having a chip-select asserted.
> */
> - if (!(mpc8xxx_spi->flags & SPI_CPM_MODE)) {
> - list_for_each_entry(t, &m->transfers, transfer_list) {
> + list_for_each_entry(t, &m->transfers, transfer_list) {
> + if (t->speed_hz != first->speed_hz) {
> + dev_err(&m->spi->dev,
> + "speed_hz cannot change during message.\n");
> + return -EINVAL;
> + }
> + if (!(mpc8xxx_spi->flags & SPI_CPM_MODE)) {
> if (t->len < 256 || t->bits_per_word != 8)
> continue;
> if ((t->len & 3) == 0)
> @@ -348,7 +361,7 @@ static int fsl_spi_prepare_message(struct spi_controller *ctlr,
> t->bits_per_word = 16;
> }
> }
> - return 0;
> + return fsl_spi_setup_transfer(m->spi, first);
> }
>
> static int fsl_spi_transfer_one(struct spi_controller *controller,

Looks good to me.

Reviewed-by: Herve Codina <herve.codina@bootlin.com>

Regards,
Hervé

--
Hervé Codina, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com

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