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List:       linux-video
Subject:    Re: Odd I2c gate code in tda1004x.c
From:       Andrew de Quincey <adq_dvb () lidskialf ! net>
Date:       2006-10-04 21:46:27
Message-ID: 200610042246.28212.adq_dvb () lidskialf ! net
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On Wednesday 04 October 2006 22:28, Hartmut Hackmann wrote:
> Hi,
>
> I stumbled over some strange code in the tda1004x_set_fe()
> function. It calls the set_params() function without
> opening the gate before but afterwards it closes it.
> So
> - the set_params() function needs to open the gate before
>    it accesses the tuner, but it doesn't need to close it.
> - _init and _sleep need to do both.
>
> This is confusing. Is there a reason why it is this way?
> I would prefer either to completely control the gate
> in the  tda1004x_set_fe() function or completely leave
> it to the board specific code.

The idea was to allow board specific code to override the default 
i2c_gate_ctrl op provided by the demodulator if a board has some /other/ gate 
mechanism on it. So a board driver can just override that op once and then 
doesn't need to care afterwards; it'll all happen automatically.  

Some gates (e.g. stv0299) auto-close after each i2c transaction. Since we were 
trying to separate the pll code from the frontend code and the board drivers 
themselves, the frontend doesn't know what the pll/tuner code is going to 
do.. it could do several transactions, each requring the gate to be opened 
each time. Therefore, it has to be up to the pll/tuner code to open the gate 
if/when it needs to. 

Finally, the reason the frontend closes it after the call was simply to ensure 
the the gate was definitely closed afterwards, if the gate happens to be of 
the type which doesn't auto-close.

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