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

[Greg Ungerer <gerg@xxxxxxxxxxxxxx>]

Hi Vladimir,

On 19/07/17 10:49, Vladimir Zapolskiy wrote:
> 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.

Thanks for the feedback.

Regards
Greg


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