Hi Tony, Komal,
> Hmmm, this sounds like a bug somewhere. TRM for 5912 says the I2C clock
> must be prescaled to be between 7 - 12 MHz [1]. The XOR input clock is
> typically 12, 13 or 19.2 MHz. So we should have code that produces:
>
> XOR Mhz Divider Prescaler
> 12 1 0
> 13 2 1
> 19.2 2 1
Not that 13 MHz cannot actually be prescaled between 7 and 12 MHz, no
matter how you look at it.
> Then again the original old code produces something different too [2]...
>
> I suspect the original code had some hw workarounds and and later code
> may have a conversion bug somewhere :)
>
> I suggest we keep the code as is for now since it's known to work on
> all omaps, and then submit a follow-up patch later once we have
> verified that that code based on the TRM works on all omaps.
I've now taken Komal's patch (#4). Here is a proposed patch which brings
the prescaler computation formula in line with your comment and table
above. It could be applied on top of Komal's patch unless it causes a
problem on some of the OMAP systems. For XOR = 13 MHz, it changes the
prescaler from 0 to 1. For XOR = 19.2 MHz it changes the prescaler from
2 to 1.
I don't have any hardware to test it, though. If it happens to be
better to be slightly over 12 MHz than slightly below 7 MHz, the
"> 12000000" condition below can be replaced with "> 14000000".
i2c: Fix OMAP clock prescaler to match the comment
Signed-off-by: Jean Delvare <[email protected]>
---
drivers/i2c/busses/i2c-omap.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
--- linux-2.6.18-rc4.orig/drivers/i2c/busses/i2c-omap.c 2006-08-10 09:56:54.000000000 +0200
+++ linux-2.6.18-rc4/drivers/i2c/busses/i2c-omap.c 2006-08-10 10:12:03.000000000 +0200
@@ -231,8 +231,8 @@
* 13 2 1
* 19.2 2 1
*/
- if (fclk_rate > 16000000)
- psc = (fclk_rate + 8000000) / 12000000;
+ if (fclk_rate > 12000000)
+ psc = fclk_rate / 12000000;
}
/* Setup clock prescaler to obtain approx 12MHz I2C module clock: */
--
Jean Delvare
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