Messages in this thread | | | From | Marek Vasut <> | Subject | Re: [PATCH] arm: remove unused code in delay.S | Date | Mon, 14 Sep 2009 18:25:55 +0200 |
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Dne Po 14. září 2009 17:50:15 Felipe Contreras napsal(a): > On Mon, Sep 14, 2009 at 6:21 PM, Russell King - ARM Linux > > <linux@arm.linux.org.uk> 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 > >> > >> <linux@arm.linux.org.uk> 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 > >> >> > >> >> <linux@arm.linux.org.uk> 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 > >> >> >> > >> >> >> <linux@arm.linux.org.uk> 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. > > 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. > > > Unless there is a strong argument for removing it, the code stays as > > is. > > > > So far, the argument is basically "it's a #if 0, we must get rid of > > it" which is a religous argument, not a technical one. The fact is > > that (as I said above) keeping it there provides the code for when > > people want to enable it. That's a technical reason for keeping it. > > > > Please can we now move to something more productive instead of this > > religous argument? > > I don't think a good argument has been stated, I'll try to do that on > Wolfram's reply. > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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