From mboxrd@z Thu Jan 1 00:00:00 1970 From: w.sang@pengutronix.de (Wolfram Sang) Date: Mon, 14 Sep 2009 17:36:16 +0200 Subject: [PATCH] arm: remove unused code in delay.S In-Reply-To: <94a0d4530909140814w36f7f5f0td2c25db07fbd4e57@mail.gmail.com> References: <1252875960-21512-1-git-send-email-felipe.contreras@gmail.com> <200909132328.47079.marek.vasut@gmail.com> <20090913230008.GC30169@n2100.arm.linux.org.uk> <20090914002100.GD30621@shareable.org> <20090914081001.GB14519@n2100.arm.linux.org.uk> <94a0d4530909140558nd8d2c47lc9954563c80a574f@mail.gmail.com> <20090914140059.GC21580@n2100.arm.linux.org.uk> <94a0d4530909140738t7e4d646r134cfd884da21348@mail.gmail.com> <20090914144028.GG21580@n2100.arm.linux.org.uk> <94a0d4530909140814w36f7f5f0td2c25db07fbd4e57@mail.gmail.com> Message-ID: <20090914153616.GD3164@pengutronix.de> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On Mon, Sep 14, 2009 at 06:14:08PM +0300, Felipe Contreras wrote: > On Mon, Sep 14, 2009 at 5:40 PM, Russell King - ARM Linux > wrote: > > On Mon, Sep 14, 2009 at 05:38:32PM +0300, Felipe Contreras wrote: > >> On Mon, Sep 14, 2009 at 5:00 PM, Russell King - ARM Linux > >> wrote: > >> > On Mon, Sep 14, 2009 at 03:58:24PM +0300, Felipe Contreras wrote: > >> >> On Mon, Sep 14, 2009 at 11:10 AM, Russell King - ARM Linux > >> >> wrote: > >> >> > On Mon, Sep 14, 2009 at 01:21:00AM +0100, Jamie Lokier wrote: > >> >> >> Russell King - ARM Linux wrote: > >> >> >> > On Sun, Sep 13, 2009 at 11:28:47PM +0200, Marek Vasut wrote: > >> >> >> > > > ? ? ? ? ? ? ? ? bhi ? ? __delay > >> >> >> > > > ? ? ? ? ? ? ? ? mov ? ? pc, lr > >> >> >> > > > ?ENDPROC(__udelay) > >> >> >> > > > > >> >> >> > > Hi > >> >> >> > > > >> >> >> > > why was this code there in the first place ? > >> >> >> > > >> >> >> > To make the delay loop more stable and predictable on older CPUs. > >> >> >> > >> >> >> So why has it been commented out, if it's needed for that? > >> >> > > >> >> > We moved on and it penalises later CPUs, leading to udelay providing > >> >> > shorter delays than requested. > >> >> > > >> >> > So the choice was either stable and predictable on older CPUs but > >> >> > buggy on newer CPUs, or correct on all CPUs but gives unnecessarily > >> >> > longer delays on older CPUs. > >> >> > >> >> Why not add an #ifdef CPU_V4 or whatever? > >> > > >> > Because then you get it whenever you configure for V4 as the lowest > >> > denominator CPU, which leads to the buggy behaviour on better CPUs. > >> > It's far better to leave it as is and just accept that the old CPUs > >> > will have longer than necessary delays. ?If people really really > >> > care (and there's likely to only be a small minority of them now) > >> > changing the '0' to a '1' is a very simple change for them to carry > >> > in their local tree. ?Unlike getting the right unrolling etc. > >> > >> Well, they can also 'git revert' this patch. If somebody really cares > >> I think they should shout now and provide a better patch, otherwise > >> this one should be merged. > > > > On the other hand, having the code there as it currently stands is not > > harmful in any way, so leaving it there is just as easy. > > It makes the code less understandable. I'm not sure about linux's > practices, but an #if 0 generally means somebody is being lazy. And what about a comment like "Try including the following code if ..."? I think I saw this somewhere else in the kernel and I'd be fine with that. So, while I generally agree that "#if 0" looks suspicious, there are a few cases for it, though they need documentation IMHO. -- Pengutronix e.K. | Wolfram Sang | Industrial Linux Solutions | http://www.pengutronix.de/ | -------------- next part -------------- A non-text attachment was scrubbed... Name: not available Type: application/pgp-signature Size: 197 bytes Desc: Digital signature URL: