Re: [PATCH] mmc: use usleep_range() in mmc_delay()

From: Sujit Reddy Thumma
Date: Mon Dec 26 2011 - 23:40:53 EST

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.

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
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
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.


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