[U-Boot] spi: mxc_spi: Set master mode for all channels

From: Fabio Estevam <fabio.estevam@freescale.com>

The glitch in the SPI clock line, which commit 3cea335c34 (spi: mxc_spi: Fix spi
clock glitch durant reset) solved, is back now and itwas re-introduced by 
commit d36b39bf0d (spi: mxc_spi: Fix ECSPI reset handling).

Actually the glitch is happening due to always toggling between slave mode
and master mode by configuring the CHANNEL_MODE bits in this reset function.

Since the spi driver only supports master mode, set the mode for all channels 
always to master mode in order to have a stable, "glitch-free" SPI clock line.

Signed-off-by: Fabio Estevam <fabio.estevam@freescale.com>
---
 drivers/spi/mxc_spi.c |   11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

Am 06.04.2013 15:15, schrieb Fabio Estevam:
> From: Fabio Estevam <fabio.estevam@freescale.com>
>
> The glitch in the SPI clock line, which commit 3cea335c34 (spi: mxc_spi: Fix spi
> clock glitch durant reset) solved, is back now and itwas re-introduced by
> commit d36b39bf0d (spi: mxc_spi: Fix ECSPI reset handling).
>
> Actually the glitch is happening due to always toggling between slave mode
> and master mode by configuring the CHANNEL_MODE bits in this reset function.
>
> Since the spi driver only supports master mode, set the mode for all channels
> always to master mode in order to have a stable, "glitch-free" SPI clock line.

Ok, thanks, I wasn't aware of this.

> Signed-off-by: Fabio Estevam <fabio.estevam@freescale.com>
> ---
>   drivers/spi/mxc_spi.c |   11 ++++++++---
>   1 file changed, 8 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/spi/mxc_spi.c b/drivers/spi/mxc_spi.c
> index 4c19e0b..9eb2bce 100644
> --- a/drivers/spi/mxc_spi.c
> +++ b/drivers/spi/mxc_spi.c
> @@ -137,9 +137,14 @@ static s32 spi_cfg_mxc(struct mxc_spi_slave *mxcs, unsigned int cs,
>   		return -1;
>   	}
>
> -	/* Reset spi */
> -	reg_write(&regs->ctrl, 0);
> -	reg_write(&regs->ctrl, MXC_CSPICTRL_EN);
> +	/*
> +	 * Reset SPI and set all CSs to master mode,

I haven't checked the rest of the driver, but do we touch the CSs bits 
anywhere else, too? Could that parts dropped with this patch, then. 
I.e. never touch the bits regs->ctrl[7-4] again?

>  if toggling
> +	 * between slave and master mode we might see a glitch
> +	 * on the clock line
> +	 */
> +	reg_write(&regs->ctrl, 0x000000F0);

Do we have a macro for the 0xF?

> +	reg_ctrl = reg_read(&regs->ctrl);

Do we expect reg_ctrl to be 0x000000F0 then? If yes, do we have to 
really read it here? If we read it here, should we drop the read 
below, then?

> +	reg_write(&regs->ctrl, reg_ctrl | MXC_CSPICTRL_EN);
>
>   	reg_ctrl = reg_read(&regs->ctrl);

So, as mentioned by Stefano before, I'd propose to either

a) do the reg_read(&regs->ctrl); only _once_. E.g.

/*
  * Reset SPI and set all CSs to master mode, if toggling
  * between slave and master mode we might see a glitch
  * on the clock line
*/
reg_write(&regs->ctrl, 0x000000F0); /* FIXME: use a macro here*/
reg_ctrl = reg_read(&regs->ctrl)  | MXC_CSPICTRL_EN; /* Reading back 
the register content is done because we don't get back the value 
written above */
reg_write(&regs->ctrl, reg_ctrl);
=> no additional read of reg_ctrl needed here as reg_ctrl contains 
already the recent register content <=


or


b) _never_ read back the register. E.g.

/*
  * Reset SPI and set all CSs to master mode, if toggling
  * between slave and master mode we might see a glitch
  * on the clock line
*/
reg_ctrl =  0x000000F0;  /* FIXME: use a macro here*/
reg_write(&regs->ctrl, reg_ctrl);
reg_ctrl |=  MXC_CSPICTRL_EN;
reg_write(&regs->ctrl, reg_ctrl);
=> no additional read of reg_ctrl needed here as reg_ctrl contains 
already the recent register content <=


Would one of these options work?

Best regards

Dirk