linux-kernel - Re: [PATCH RFT] regulator: max8972: Fix setting ramp delay

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Date:	Mon, 30 May 2016 16:52:12 +0800
From:	Axel Lin <axel.lin@...ics.com>
To:	Krzysztof Kozlowski <k.kozlowski@...sung.com>
Cc:	Mark Brown <broonie@...nel.org>,
	Laxman Dewangan <ldewangan@...dia.com>,
	Mikko Perttunen <mperttunen@...dia.com>,
	Liam Girdwood <lgirdwood@...il.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH RFT] regulator: max8972: Fix setting ramp delay

2016-05-30 16:48 GMT+08:00 Krzysztof Kozlowski <k.kozlowski@...sung.com>:
> On 05/29/2016 01:16 PM, Axel Lin wrote:
>> Current code can set ramp delay to a wrong setting that the return value
>> from .set_voltage_time_sel is not enough for proper delay.
>
> I don't understand what yo wanted to say here. What wrong setting is
> possible? Why do you mention set_voltage_time_sel() here?
>
> Can you elaborate?
>
> The only difference I spotted is how you round up the ramp_delay values.

Assume rdev->constraints->ramp_delay is 20000.

Original code will set MAX8973_RAMP_12mV_PER_US.

However, in regulator_set_voltage_time_sel()
        return DIV_ROUND_UP(abs(new_volt - old_volt), ramp_delay);

This return value is not enough if the device is using MAX8973_RAMP_12mV_PER_US
setting.