Re: [PATCH] I2C: i.MX: early: Use a custom delay on i.MX6

[Sascha Hauer <sha@pengutronix.de>]

On Wed, Feb 01, 2023 at 08:44:35PM +1100, John Watts wrote:
> The i.MX early I2C code requires waiting for the controller to settle
> after configuration. This is currently done using udelay which is
> supported on ARMv8 but not on ARMv7.
> 
> For the i.MX6 we will have to use a custom delay. This was only
> tested on the i.MX6Q but should work on all other i.MX6 chips.
> 
> Signed-off-by: John Watts <contact@jookia.org>
> ---
>  drivers/i2c/busses/i2c-imx-early.c | 24 +++++++++++++++++++++++-
>  1 file changed, 23 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/i2c/busses/i2c-imx-early.c b/drivers/i2c/busses/i2c-imx-early.c
> index 6c8bdc7904..30cc65ca86 100644
> --- a/drivers/i2c/busses/i2c-imx-early.c
> +++ b/drivers/i2c/busses/i2c-imx-early.c
> @@ -90,6 +90,28 @@ static int i2c_fsl_acked(struct fsl_i2c *fsl_i2c)
>  	return i2c_fsl_poll_status(fsl_i2c, 0, I2SR_RXAK);
>  }
>  
> +static void i2c_fsl_settle(struct fsl_i2c *fsl_i2c)
> +{
> +#ifdef CPU_ARCH_ARMv8
> +	udelay(100);
> +#else
> +	/*
> +	 * We lack udelay on the i.MX6 prebootloader, so delay
> +	 * manually: On an i.MX6 with a 66Mhz I2C peripheral clock
> +	 * one cycle of this loop takes 1.30us,
> +	 * this means we have to wait for 76.9 microseconds.
> +	 *
> +	 * This clock may be 44Mhz if the BT_FREQ eFUSE is set,
> +	 * this just means it will take 150 microseconds.
> +	 */

I rounded up to 100 cycles and rephrased this to be a little less i.MX6
centric:

	/*
	 * We lack udelay on the 32bit i.MX SoCs, so delay manually: On an
	 * i.MX6 with a 66Mhz I2C peripheral clock one cycle of this loop
	 * takes 1.30us. Let's be generous and round up to 100 cycles. Other
	 * i.MX SoCs do not have a higher peripheral clock, so we should be
	 * safe here as well.
	 */

In the end it doesn't hurt when it takes a little longer.

Applied, thanks

Sascha

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