Re: [PATCH 4/9] thermal: rockchip: handle the power sequence for tsadc controller

From: Caesar Wang <caesar.upstream@gmail.com>
To: Eduardo Valentin <edubezval@gmail.com>
Cc: Caesar Wang <caesar.upstream@gmail.com>,
	Heiko Stuebner <heiko@sntech.de>,
	linux-pm@vger.kernel.org, dianders@chromium.org,
	linux-kernel@vger.kernel.org, linux-rockchip@lists.infradead.org,
	smbarber@google.com, briannorris@google.com,
	Zhang Rui <rui.zhang@intel.com>,
	linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH 4/9] thermal: rockchip: handle the power sequence for tsadc controller
Date: Tue, 3 May 2016 10:27:26 +0800	[thread overview]
Message-ID: <57280C8E.5080406@gmail.com> (raw)
In-Reply-To: <20160428150432.GA20009@localhost.localdomain>

在 2016年04月28日 23:04, Eduardo Valentin 写道:
> On Thu, Apr 28, 2016 at 09:50:29AM +0800, Caesar Wang wrote:
>>
>> 在 2016年04月28日 07:48, Eduardo Valentin 写道:
>>> On Mon, Apr 18, 2016 at 11:35:56AM +0800, Caesar Wang wrote:
>>>> +		regmap_write(grf, GRF_TSADC_TESTBIT_L, GRF_TSADC_TSEN_PD_ON);
>>>> +		mdelay(10);
>>>> +		regmap_write(grf, GRF_TSADC_TESTBIT_L, GRF_TSADC_TSEN_PD_OFF);
>>>> +		udelay(100); /* The spec note says at least 15 us */
>>>> +		regmap_write(grf, GRF_SARADC_TESTBIT, GRF_SARADC_TESTBIT_ON);
>>>> +		regmap_write(grf, GRF_TSADC_TESTBIT_H, GRF_TSADC_TESTBIT_H_ON);
>>>> +		udelay(200); /* The spec note says at least 90 us */
>>> Does it make sense to use usleep_range() instead?
>> I think so in the past, but I'm digging into the the udelay/usleep for
>> kernel.
> What do you mean by in the past? timekeeping doc still recommends the
> range 10us to 20ms for usleep_range()
>
>> In general,
>>
>> udelay < 10us ~100us
>> mdelay > 1m, <1000ms/HZ
>> usleep_range(min,max) > 100us, <20ms
> even here, your udelays could be replaced by usleep_range().
>
> Any particular reason you believe spining is better than sleeping in
> your case?
>
>> msleep > 20ms,  < 1000ms
>>
>> So the udelay is suit for tsadc power sequence.
>> ---
>>
>>
>> Also,  we have used the mdelay(10), so it doesn't matter if use the udelay.
>> After all the udelay is stable than the usleep_range.
> What do you mean udelay is stable than usleep_range? usleep_range will
> give the opportunity to the scheduler to coalesce wakeups. udelay is a
> busyloop spin. Besides, I am not sure the current situation, but
> busylooping may be affected by cpu frequency.

Okay, thanks for pointing out.

Send the fixes patch on https://patchwork.kernel.org/patch/8999971/

Thank you!

-Caesar
>
>> -Caesar
>>
>>> 1.9.1
>>>
>>>
>>>
>>>
>>> -- 
>>> Thanks,
>>> Caesar
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> http://lists.infradead.org/mailman/listinfo/linux-rockchip

-- 
Thanks,
Caesar