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

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Date:	Wed, 24 Sep 2014 10:51:53 +0800
From:	Chris Zhong <zyw@...k-chips.com>
To:	Doug Anderson <dianders@...omium.org>
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


On 09/24/2014 10:13 AM, Doug Anderson wrote:
> 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
>
If we want pwm stay enabled at boot(FW left it), needn't to modify 
anything, only need to init pwm duty in FW.
And now reading the duty from pwm would make sense.



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