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

[Vladimir Zapolskiy <vz@xxxxxxxxx>]

Hello Greg,

On 07/11/2017 07:22 AM, Greg Ungerer 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);
>  
> 

FWIW I still didn't manage to utilize the second and so on native chip
selects on DT-only i.MX31 (master->num_chipselect value is preset to 1
if I remember correctly), but the experienced problem is not related
to the change and it should be addressed separately.

So,

Reviewed-by: Vladimir Zapolskiy <vz@xxxxxxxxx>
Tested-by: Vladimir Zapolskiy <vz@xxxxxxxxx>

Thank you for the change.

--
With best wishes,
Vladimir
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