Re: [PATCH V2 6/9] spi: bcm2835aux: warn in dmesg that native cs is not really supported

Stefan Wahren
2019-03-25T10:28:31Z

Hi Martin,

Am 24.03.19 um 18:49 schrieb kernel@martin.sperl.org:
> From: Martin Sperl <kernel@martin.sperl.org>
>
> From personal bad experience (even as the author of the original driver)
> it shows that native-cs is "somewhat" supported by the spi bus driver
> when using a buggy device tree.
>
> So make sure that the driver is warning in dmesg about this fact
> that we are running in a not supported mode that may have surprizing
> limitations.
>
> Signed-off-by: Martin Sperl <kernel@martin.sperl.org>
> Fixes: 1ea29b39f4c812ece2f936065a0a3d6fe44a263e
please use a proper fixes tag.
> ---
> drivers/spi/spi-bcm2835aux.c | 33 +++++++++++++++++++++++++++++++++
> 1 file changed, 33 insertions(+)
>
> diff --git a/drivers/spi/spi-bcm2835aux.c b/drivers/spi/spi-bcm2835aux.c
> index c8acde017b6a..6af07dec5fdc 100644
> --- a/drivers/spi/spi-bcm2835aux.c
> +++ b/drivers/spi/spi-bcm2835aux.c
> @@ -396,6 +396,38 @@ static void bcm2835aux_spi_handle_err(struct spi_master *master,
> bcm2835aux_spi_reset_hw(bs);
> }
>
> +static int bcm2835aux_spi_setup(struct spi_device *spi)
> +{
> + int ret;
> +
> + if (spi->mode & SPI_NO_CS)
> + return 0;
> + /* sanity check for native cs */
> + if (!gpio_is_valid(spi->cs_gpio)) {
> + /* for dt-backwards compatibility: only support native on CS0
> + * known things not supported with broken native CS:
> + * * multiple chip-selects: cs0-cs2 are all
> + * simultaniously asserted whenever there is a transfer
> + * this even includes SPI_NO_CS
> + * * SPI_CS_HIGH: cs are always asserted low
> + * * cs_change: cs is deasserted after each spi_transfer
> + * * cs_delay_usec: cs is always deasserted one SCK cycle
> + * after the last transfer
> + * probably more...
> + */
> + if (spi->chip_select == 0) {
> + dev_err(&spi->dev,
> + "native CS is not supported but may work for some use-cases for cs = 0 - please define a valid value cs-gpios in DT for complete feature set\n");
> + return 0;

These messages are rather too long, please keep it in the ~ 80 char
limit (in source code and dmesg).
Or make it two lines ...

Since we return with 0, i prefer to use dev_warn instead of dev_err.

Thanks

> + }
> + dev_err(&spi->dev,
> + "native CS is not supported for cs > 0 - please define a valid value cs-gpios in DT to enable multiple cs\n");
> + return -EINVAL;
> + }
> +
> + return 0;
> +}
> +