Re: [PATCHv3 1/2] spi: imx: fix use of native chip-selects with devicetree

[Fabio Estevam <festevam@xxxxxxxxx>]

Adding Pengutronix folks on Cc.

On Tue, Jul 11, 2017 at 1:22 AM, Greg Ungerer <gerg@xxxxxxxxxxxxxx> wrote:
> The commonly used mechanism of specifying the hardware or native
> chip-select on an SPI device in devicetree (that is "cs-gpios = <0>")
> does not result in the native chip-select being configured for use.
> So external SPI devices that require use of the native chip-select
> will not work.
>
> You can successfully specify native chip-selects if using a platform
> setup by specifying the cs-gpio as negative offset by 32. And that
> works correctly. You cannot use the same method in devicetree.
>
> The logic in the spi-imx.c driver during probe uses core spi function
> of_spi_register_master() in spi.c to parse the "cs-gpios" devicetree tag.
> For valid GPIO values that will be recorded for use, all other entries in
> the cs_gpios list will be set to -ENOENT. So entries like "<0>" will be
> set to -ENOENT in the cs_gpios list.
>
> When the SPI device registers are setup the code will use the GPIO
> listed in the cs_gpios list for the desired chip-select. If the cs_gpio
> is less then 0 then it is intended to be for a native chip-select, and
> its cs_gpio value is added to 32 to get the chipselect number to use.
> Problem is that with devicetree this can only ever be -ENOENT (which
> is -2), and that alone results in an invalid chip-select number. But also
> doesn't allow selection of the native chip-select at all.
>
> To fix, if the cs_gpio specified for this spi device is not a
> valid GPIO then use the "chip_select" (that is the native chip-select
> number) for hardware setup.
>
> Signed-off-by: Greg Ungerer <gerg@xxxxxxxxxxxxxx>
> ---
>  drivers/spi/spi-imx.c | 8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/spi/spi-imx.c b/drivers/spi/spi-imx.c
> index b402530..f4fe66c 100644
> --- a/drivers/spi/spi-imx.c
> +++ b/drivers/spi/spi-imx.c
> @@ -524,8 +524,8 @@ static int mx31_config(struct spi_device *spi, struct spi_imx_config *config)
>                 reg |= MX31_CSPICTRL_POL;
>         if (spi->mode & SPI_CS_HIGH)
>                 reg |= MX31_CSPICTRL_SSPOL;
> -       if (spi->cs_gpio < 0)
> -               reg |= (spi->cs_gpio + 32) <<
> +       if (!gpio_is_valid(spi->cs_gpio))
> +               reg |= (spi->chip_select) <<
>                         (is_imx35_cspi(spi_imx) ? MX35_CSPICTRL_CS_SHIFT :
>                                                   MX31_CSPICTRL_CS_SHIFT);
>
> @@ -616,8 +616,8 @@ static int mx21_config(struct spi_device *spi, struct spi_imx_config *config)
>                 reg |= MX21_CSPICTRL_POL;
>         if (spi->mode & SPI_CS_HIGH)
>                 reg |= MX21_CSPICTRL_SSPOL;
> -       if (spi->cs_gpio < 0)
> -               reg |= (spi->cs_gpio + 32) << MX21_CSPICTRL_CS_SHIFT;
> +       if (!gpio_is_valid(spi->cs_gpio))
> +               reg |= spi->chip_select << MX21_CSPICTRL_CS_SHIFT;
>
>         writel(reg, spi_imx->base + MXC_CSPICTRL);
>
> --
> 1.9.1
>
> --
> To unsubscribe from this list: send the line "unsubscribe linux-spi" in
> the body of a message to majordomo@xxxxxxxxxxxxxxx
> More majordomo info at  http://vger.kernel.org/majordomo-info.html
--
To unsubscribe from this list: send the line "unsubscribe linux-spi" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html