From mboxrd@z Thu Jan 1 00:00:00 1970 From: felipe.contreras@gmail.com (Felipe Contreras) Date: Mon, 14 Sep 2009 19:54:54 +0300 Subject: [PATCH] arm: remove unused code in delay.S In-Reply-To: <200909141825.55239.marek.vasut@gmail.com> References: <1252875960-21512-1-git-send-email-felipe.contreras@gmail.com> <20090914152129.GI21580@n2100.arm.linux.org.uk> <94a0d4530909140850h3ec1bde2ifc05ff7d340f96fe@mail.gmail.com> <200909141825.55239.marek.vasut@gmail.com> Message-ID: <94a0d4530909140954u1217e27dq7b21bb883a75753b@mail.gmail.com> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On Mon, Sep 14, 2009 at 7:25 PM, Marek Vasut wrote: > Dne Po 14. z??? 2009 17:50:15 Felipe Contreras napsal(a): >> On Mon, Sep 14, 2009 at 6:21 PM, Russell King - ARM Linux >> >> wrote: >> > 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. >> > >> > I would agree with you if it was a complicated bit of code, but it >> > isn't. ?It is a simple count to zero (or overflow) and terminate >> > loop. ?And it's certainly not about me being lazy. > > Russell, what about adding a comment somewhere explaining why it's there? That'd > be a fine fix I think. >> >> Maybe it's not complicated to you, but not everyone is so literate >> about ARM assembly code (e.g. me). When I first looked at the code I >> didn't even realize there was an #if 0 there, which yes, I grant is a >> problem of my editor, but the issue wouldn't have happened if the code >> wasn't there in the first place. > > This is still religious argument and or your problem -- fix your editor. I'm an example user. I'm pretty sure there's other vim users out there :) Since I'm not touching the 'asm' configurations I'm assuming many other people will see the code as I do. Not my main argument, anyway. >> And I'm not saying your are being lazy, if anything it's probably the >> people using this code. They should figure a way to avoid patching the >> code. However, these users are hypothetical at this point. > > If you could invest your time into investigating how to make this configurable > instead of arguing about #if 0, it'd be awesome. That's what I'm doing, so far I haven't heard any suggestions on how to do that. -- Felipe Contreras