Hi Wolfram,
On Mon, Feb 23, 2015 at 02:07:18PM +0100, Wolfram Sang wrote:
> Hi,
>
> On 2015-02-15 15:43, Yoshihiro Kaneko wrote:
> >From: Ryo Kataoka <[email protected]>
> >
> >In case of repeated START condition, the restart has to be kicked
> >before clear status (MSR register). If it is kicked after clear status,
> >R-Car I2C may transfer data (TXD register) or receive data (RXD register)
> >instead of transferring slave address (MAR register).
> >
> >Signed-off-by: Ryo Kataoka <[email protected]>
> >Signed-off-by: Yoshihiro Kaneko <[email protected]>
>
> Thanks for the patch!
>
> I wondered if we couldn't always kick the start/restart before clearing
> the status register?
I asked Kataoka-san about this and his response was as follows:
If system(CPU) is busy, the driver can't clear the status register soon
after kicking start.
If sequence of first start is as follows, there is a problem.
Because H/W starts by 1.
But sequence of re-start is as follows, there is no problem.
Because H/W starts by 2.
1. Issue START condition by ESG bit of ICMCR register.
<--- If there is too much time, H/W finish transmitting
and set status in status register.
2. Clear interrupt status (ICMSR).
3. Open interrupt mask.
4. Wait interrupt.
<--- If status is cleared, interrupt does not occur.
> I am not sure if this simulates the flaw accurately, but I inserted a
> udelay(500) in the original code after clearing the status register.
> Then, I couldn't access the audio codec on my Lager board anymore. By
> always first "kicking" and then clearing, access was possible again. But
> as said, I am not sure if my scenario matches yours. Have you considered
> to treat start and repeated start the same and always kick the condition
> before clearing the status?
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