linux-kernel - Re: [PATCH v6 1/2] regulator: st-pwm: get voltage and duty table from dts

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Date:	Tue, 23 Sep 2014 19:13:06 -0700
From:	Doug Anderson <dianders@...omium.org>
To:	Chris Zhong <zyw@...k-chips.com>
Cc:	Heiko Stübner <heiko@...ech.de>,
	linux-rockchip@...ts.infradead.org,
	Lee Jones <lee.jones@...aro.org>,
	"broonie@...nel.org" <broonie@...nel.org>,
	Liam Girdwood <lgirdwood@...il.com>,
	Grant Likely <grant.likely@...aro.org>,
	Rob Herring <robh+dt@...nel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>
Subject: Re: [PATCH v6 1/2] regulator: st-pwm: get voltage and duty table from dts

Chris,

On Tue, Sep 23, 2014 at 6:47 PM, Chris Zhong <zyw@...k-chips.com> wrote:
>
> On 09/24/2014 07:43 AM, Doug Anderson wrote:
>>
>> Chris,
>>
>> On Tue, Sep 23, 2014 at 8:53 AM, Chris Zhong <zyw@...k-chips.com> wrote:
>>>
>>> Get voltage & duty table from device tree might be better, other
>>> platforms can also use this
>>> driver without any modify.
>>>
>>> Signed-off-by: Chris Zhong <zyw@...k-chips.com>
>>> Reviewed-by: Doug Anderson <dianders@...omium.org>
>>
>> I finally managed to get everything setup and I've now tested this
>> myself on an rk3288-based board.
>>
>> Tested-by: Doug Anderson <dianders@...omium.org>
>>
>> I'd imagine the next step is for Lee to comment on the patch and when
>> he's happy with it Mark Brown will land it?
>>
>>
>> One thing that's still a bit odd (though no different than the
>> behavior of the driver from before you touched it, so it shouldn't
>> block landing IMHO) is that at boot time this regulator will report
>> that it's at the highest voltage but the voltage won't actually change
>> until the first client sets the voltage.
>
> Yes, I knew this problem, since the default of duty cycle is 0, not a true
> value.
> If we can get duty from pwm, this regulator will report a correct voltage.

I don't think it's possible in all cases to figure out what the
voltage was before this regulator was probed.

* pin might have been input w/ pullup, pulldown, or no pull
* pin might have been driven high or driven low

In that case trying to read the duty from the pwm wouldn't make sense.
...but I guess you could add a property to the PWM driver to say that
it stays enabled at boot if the FW left it enabled (and keep the same
duty cycle / clocks?).  That would at least solve the problem where
the firmware configured the PWM and left it in a specific state even
if it doesn't solve the above problem...


-Doug
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