From mboxrd@z Thu Jan 1 00:00:00 1970 From: Rafal Prylowski Subject: Re: [PATCH v2 1/3] PATA host controller driver for ep93xx Date: Wed, 04 Apr 2012 17:16:30 +0200 Message-ID: <4F7C65CE.6000309@metasoft.pl> References: <4F7B0C54.8010804@metasoft.pl> <201204032008.00509.arnd@arndb.de> <4F7C4142.1010709@metasoft.pl> <201204041323.36695.arnd@arndb.de> <4F7C64B8.5000909@metasoft.pl> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-2 Content-Transfer-Encoding: 7bit Return-path: Received: from metasoft.pl ([195.149.224.191]:59903 "EHLO smtp.metasoft.pl" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756672Ab2DDPRa (ORCPT ); Wed, 4 Apr 2012 11:17:30 -0400 In-Reply-To: <4F7C64B8.5000909@metasoft.pl> Sender: linux-ide-owner@vger.kernel.org List-Id: linux-ide@vger.kernel.org To: Arnd Bergmann Cc: linux-arm-kernel@lists.infradead.org, H Hartley Sweeten , "linux-ide@vger.kernel.org" , Sergei Shtylyov , "bzolnier@gmail.com" , "rmallon@gmail.com" , "joao.ramos@inov.pt" On 2012-04-04 17:11, Rafal Prylowski wrote: > On 2012-04-04 15:23, Arnd Bergmann wrote: >> On Wednesday 04 April 2012, Rafal Prylowski wrote: >>> On 2012-04-03 22:08, Arnd Bergmann wrote: >>>>>> +static void ep93xx_pata_wait_for_iordy(void __iomem *base) >>>>>> +{ >>>>>> + unsigned long deadline = jiffies + msecs_to_jiffies(1000); >>>>>> + while (!ep93xx_pata_check_iordy(base) && >>>>>> + time_is_before_jiffies(deadline)) >>>>>> + cpu_relax(); >>>>>> +} >>>> >>>> Much better for a delay than the previous version. However, it's >>>> still a busy wait, which is bad for realtime behavior, especially >>>> since this can potentially take many milliseconds. If possible, >>>> it should have an msleep() or at least cond_resched() instead of >>>> the cpu_relax(). Obviously that will only work when no spinlocks >>>> are held. >>>> >>> >>> Unfortunately, we can't use msleep() or cond_resched() here >>> - ep93xx_pata_wait_for_iordy() is called from interrupt handler. >> >> Well, it also seems inappropriate to have a one second delay timeout >> inside of the interrupt handler. >> >> I suppose if you are emulating what a regular read of the status >> register does, there isn't much to improve here though. >> >> Arnd > > According to ATA specification, maximum IORDY pulse width is 1250ns, > so I'll set timeout to 2ms (I should check this before posting the driver..). 2ms is far too big value... Should be 2us. RP