Re: [patch] Fix AF9015 Dual tuner i2c write failures

[Antti Palosaari <crope@iki.fi>]

Wow, thanks!

On 03/04/2011 11:37 PM, Andrew de Quincey wrote:
> Hi, this has been annoying me for some time, so this evening I fixed
> it. If you use one of the above dual tuner devices (e.g. KWorld 399U),
> you get random tuning failures and i2c errors reported in dmesg such
> as:
[...]
> Adding a "bus lock" to af9015_i2c_xfer() will not work as demod/tuner
> accesses will take multiple i2c transactions.
>
> Therefore, the following patch overrides the dvb_frontend_ops
> functions to add a per-device lock around them: only one frontend can
> now use the i2c bus at a time. Testing with the scripts above shows
> this has eliminated the errors.

This have annoyed me too, but since it does not broken functionality 
much I haven't put much effort for fixing it. I like that fix since it 
is in AF9015 driver where it logically belongs to. But it looks still 
rather complex. I see you have also considered "bus lock" to 
af9015_i2c_xfer() which could be much smaller in code size (that's I 
have tried to implement long time back).

I would like to ask if it possible to check I2C gate open / close inside 
af9015_i2c_xfer() and lock according that? Something like:

typical command sequence:
 >> FE0 open gate
 >> FE0 write reg
 >> FE0 close gate
 >> FE1 open gate
 >> FE1 read reg
 >> FE1 close gate

if (locked == YES)
   if (locked_by != caller FE)
     return error locked by other FE
   else (locked_by == caller FE)
     allow reg access
     if (gate close req)
       locked = NO
       locked_by = NONE
else (locked == NO)
   locked = YES
   locked_by = caller FE
   allow reg access

Do you see it possible?

thanks
Antti
-- 
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