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

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

[Uwe Kleine-König]

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@pengutronix.de>
---
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.

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


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

[Uwe Kleine-König]

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/  |

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

[Mark Brown]

On Thu, Jul 05, 2012 at 09:45:40AM +0200, Uwe Kleine-K?nig wrote:
> On Thu, Feb 09, 2012 at 10:21:45PM +0100, Uwe Kleine-K?nig 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-K?nig <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

You probably want to resend this with Linus W in the CCs.

> 
> > 
> > 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-K?nig            |
> Industrial Linux Solutions                 | http://www.pengutronix.de/  |
> 
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Re: [PATCH RFC] spi/gpio: start with CS non-active

[Linus Walleij]

On Mon, Jul 9, 2012 at 2:08 PM, Mark Brown <broonie-GFdadSzt00ze9xe1eoZjHA@public.gmane.org> wrote:
> On Thu, Jul 05, 2012 at 09:45:40AM +0200, Uwe Kleine-K?nig wrote:
>> On Thu, Feb 09, 2012 at 10:21:45PM +0100, Uwe Kleine-K?nig 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-K?nig <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
>
> You probably want to resend this with Linus W in the CCs.

It all makes sense to me so:
Acked-by: Linus Walleij <linus.walleij-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org>

Now the SPI maintainer needs to pick it up though, if your proposal
to pick it up goes through this patch is all yours now.

Yours,
Linus Walleij

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