Re: [linux-2.6 PATCH 1/1] i2c-i801: Re-read busy bit and wait for transaction to complete

[Chaitanya Lala <clala-DUeqMYwuH4dWk0Htik3J/w@public.gmane.org>]

Hi Jean,

Jean Delvare wrote:
> Hi Chaitanya,
>
> On Tue, 15 Sep 2009 10:34:56 -0700, Chaitanya Lala wrote:
>   
>> I tried your patch and preliminary results look encouraging.
>> Will let you know about the final results in a few days.
>>     
>
> OK, thanks.
>
>   
>> One question - Are we sure that msleep(2) would fix the glitch for good ?
>> I am not very clear about the timings constraints of the i2c bus, hence 
>> the query.
>>     
>
> It doesn't have anything to do with I2C bus timings. The msleep() is
> between the beginning of the transaction and the polling for result.
> This is between the OS and the SMBus controller. The bus timings
> themselves are solely handled by the SMBus controller in hardware and
> we don't have to deal with it at all.
>
> The msleep(1) has been there for a long time, back when HZ was
> hard-coded to 100. This means we used to wait for at least 10 ms. With
> HZ values increasing, the same code results in shorter sleeps (down to
> 1 ms). So maybe 1 ms wasn't sufficient and 2 ms will be. That being
> said, if you didn't use HZ=1000... At HZ=250 and HZ=100, msleep(1) and
> msleep(2) are the same, so I would be surprised if my patch really
> helps for these values of HZ. I expected your problems to happen at
> HZ=1000.
>   

Thanks for the explanation.

> But please keep testing, and report what you find. If my patch doesn't
> help, you could try with msleep(3) or msleep(4) and see if that helps.
>
>   

Will continue testing and let you know soon.

Thanks,
Chaitanya