linux-kernel - Re: [PATCH] mmc: use usleep_range() in mmc

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Date:	Tue, 27 Dec 2011 10:10:25 +0530
From:	Sujit Reddy Thumma <sthumma@...eaurora.org>
To:	Dmitry Antipov <dmitry.antipov@...aro.org>
CC:	linaro-dev@...ts.linaro.org, patches@...aro.org,
	linux-mmc@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mmc: use usleep_range() in mmc_delay()

Hi Antipov,

Sorry for the delayed response. Please find some comments below:

On 12/21/2011 6:35 PM, Dmitry Antipov wrote:
> On 12/21/2011 03:25 PM, Sujit Reddy Thumma wrote:
>
>> I have posted similar patch some time back.
>> http://comments.gmane.org/gmane.linux.ports.arm.msm/2119.
>>
>> Would you like to comment on that?
>
> - I believe we should forget about jiffies, HZ and other similar obsolete
> timekeeping stuff;
>
> - I have no ideas where did you get 'most typical' 20 ms. MMC subsystem
> uses
> mmc_delay() with two compile-time fixed values 1 and 10 ms, with the only
> exception of card-dependent sleep/awake timeout. I was unable to find a
> table
> with typical values, but it's rounded up to >= 1 ms anyway.

The main aim of my patch was to fix mmc_delay() to give accurate delay.
You might want to refer to Documentation/timers/timers-howto.txt 
(Section: SLEEPING FOR ~USECS OR SMALL MSECS) to know why usleep_range() 
must be used instead of msleep for delays less than 20ms (or more 
accurately two jiffies, since in HZ=100 systems this comes to 20ms).

Also, in the documentation it is suggested that for delays greater than 
10ms+ use msleep(). Although MMC subsystem doesn't use mmc_delay() for 
greater than 10ms today but I guess we should keep it for future purpose 
and just not have only usleep_range() as your patch did.

>
> Dmitry

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