From mboxrd@z Thu Jan 1 00:00:00 1970 From: Sujit Reddy Thumma Subject: Re: [PATCH] mmc: use usleep_range() in mmc_delay() Date: Tue, 27 Dec 2011 10:10:25 +0530 Message-ID: <4EF94C39.3070705@codeaurora.org> References: <4EF18310.6080801@linaro.org> <4EF1C230.6060005@codeaurora.org> <4EF1D97E.3000201@linaro.org> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Return-path: Received: from wolverine02.qualcomm.com ([199.106.114.251]:29080 "EHLO wolverine02.qualcomm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753881Ab1L0Eka (ORCPT ); Mon, 26 Dec 2011 23:40:30 -0500 In-Reply-To: <4EF1D97E.3000201@linaro.org> Sender: linux-mmc-owner@vger.kernel.org List-Id: linux-mmc@vger.kernel.org To: Dmitry Antipov Cc: linaro-dev@lists.linaro.org, patches@linaro.org, linux-mmc@vger.kernel.org, linux-kernel@vger.kernel.org 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