Re: [PATCH] i2c: scx200_acb: avoid I2C bus overclocking.

[Wolfram Sang <wsa-z923LK4zBo2bacvFa/9K2g@public.gmane.org>]

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On Thu, Apr 23, 2015 at 10:27:50PM +0200, Svenning Sørensen wrote:
> According to I2C spec, max SCL rate is 100 kHz, but SCx200/CS5536
> controller is currently driving it at 214 kHz according to my math.
> 
> SCL is derived from an input clock of 48 MHz, which must be divided
> by 480 (240 cycles for each SCL high/low state) to be within spec.
> 
> Signed-off-by: Svenning Soerensen <sss-sijd2F9aCfdBDgjK7y7TUQ@public.gmane.org>

Thanks for mentioning that it fixed a problem for you. I needed this
info.

> +#define ACBCLK		240	/* 48 MHz / 100 kHz / 2 */

Can you add a comment where you found the info about 48MHz? Since I
don't know the hardware at all: Can you imagine that there is even older
hardware with a clock where 0x70 was suitable?

> -	outb(inb(ACBCTL2) | ACBCTL2_ENABLE, ACBCTL2);
> +	outb(ACBCLK | ACBCTL2_ENABLE, ACBCTL2);
...
> -	outb(inb(ACBCTL2) | ACBCTL2_ENABLE, ACBCTL2);
> +	outb(ACBCLK | ACBCTL2_ENABLE, ACBCTL2);

For consistency reasons and to be less intrusive, I'd rather keep the
original chunks.


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