Re: [PATCH RFC] spi/gpio: start with CS non-active

["Uwe Kleine-König" <u.kleine-koenig-bIcnvbaLZ9MEGnE8C9+IrQ@public.gmane.org>]

On Thu, Feb 09, 2012 at 10:21:45PM +0100, Uwe Kleine-König wrote:
> The chip select line was configured as output with the initial value
> being active explicitly. It was later deasserted during
> spi_bitbang_setup() without any clock activity in between. So it makes
> no sense to activate the device at all and the chip select line can
> better start non-active.
> 
> Signed-off-by: Uwe Kleine-König <u.kleine-koenig-bIcnvbaLZ9MEGnE8C9+IrQ@public.gmane.org>
> ---
> Hello,
> 
> I'm not sure if an active chip select line without any clock activity can
> confuse a device. If so, this patch might qualify as fix. But with my
> limited knowledge about spi it's also possible that I just miss why the
> active chip select is important. For the devices I have it doesn't seem
> to make a difference.
ping

> 
> Best regards
> Uwe
> 
>  drivers/spi/spi-gpio.c |    3 ++-
>  1 files changed, 2 insertions(+), 1 deletions(-)
> 
> diff --git a/drivers/spi/spi-gpio.c b/drivers/spi/spi-gpio.c
> index 0094c64..0b56cfc 100644
> --- a/drivers/spi/spi-gpio.c
> +++ b/drivers/spi/spi-gpio.c
> @@ -235,7 +235,8 @@ static int spi_gpio_setup(struct spi_device *spi)
>  			status = gpio_request(cs, dev_name(&spi->dev));
>  			if (status)
>  				return status;
> -			status = gpio_direction_output(cs, spi->mode & SPI_CS_HIGH);
> +			status = gpio_direction_output(cs,
> +					!(spi->mode & SPI_CS_HIGH));
>  		}
>  	}
>  	if (!status)
> -- 
> 1.7.9
> 
> 

-- 
Pengutronix e.K.                           | Uwe Kleine-König            |
Industrial Linux Solutions                 | http://www.pengutronix.de/  |

------------------------------------------------------------------------------
Live Security Virtual Conference
Exclusive live event will cover all the ways today's security and 
threat landscape has changed and how IT managers can respond. Discussions 
will include endpoint security, mobile security and the latest in malware 
threats. http://www.accelacomm.com/jaw/sfrnl04242012/114/50122263/