Re: [PATCH] arm: remove unused code in delay.S
From: Russell King - ARM Linux
Date: Mon Sep 14 2009 - 11:21:50 EST
On Mon, Sep 14, 2009 at 06:14:08PM +0300, Felipe Contreras wrote:
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On Mon, Sep 14, 2009 at 5:40 PM, Russell King - ARM Linux
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<linux@xxxxxxxxxxxxxxxx> wrote:
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> On Mon, Sep 14, 2009 at 05:38:32PM +0300, Felipe Contreras wrote:
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>> On Mon, Sep 14, 2009 at 5:00 PM, Russell King - ARM Linux
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>> <linux@xxxxxxxxxxxxxxxx> wrote:
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>> > On Mon, Sep 14, 2009 at 03:58:24PM +0300, Felipe Contreras wrote:
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>> >> On Mon, Sep 14, 2009 at 11:10 AM, Russell King - ARM Linux
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>> >> <linux@xxxxxxxxxxxxxxxx> wrote:
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>> >> > On Mon, Sep 14, 2009 at 01:21:00AM +0100, Jamie Lokier wrote:
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>> >> >> Russell King - ARM Linux wrote:
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>> >> >> > On Sun, Sep 13, 2009 at 11:28:47PM +0200, Marek Vasut wrote:
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>> >> >> > > > bhi __delay
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>> >> >> > > > mov pc, lr
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>> >> >> > > > ENDPROC(__udelay)
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>> >> >> > > >
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>> >> >> > > Hi
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>> >> >> > >
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>> >> >> > > why was this code there in the first place ?
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>> >> >> >
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>> >> >> > To make the delay loop more stable and predictable on older CPUs.
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>> >> >>
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>> >> >> So why has it been commented out, if it's needed for that?
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>> >> >
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>> >> > We moved on and it penalises later CPUs, leading to udelay providing
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>> >> > shorter delays than requested.
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>> >> >
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>> >> > So the choice was either stable and predictable on older CPUs but
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>> >> > buggy on newer CPUs, or correct on all CPUs but gives unnecessarily
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>> >> > longer delays on older CPUs.
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>> >>
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>> >> Why not add an #ifdef CPU_V4 or whatever?
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>> >
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>> > Because then you get it whenever you configure for V4 as the lowest
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>> > denominator CPU, which leads to the buggy behaviour on better CPUs.
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>> > It's far better to leave it as is and just accept that the old CPUs
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>> > will have longer than necessary delays. If people really really
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>> > care (and there's likely to only be a small minority of them now)
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>> > changing the '0' to a '1' is a very simple change for them to carry
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>> > in their local tree. Unlike getting the right unrolling etc.
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>>
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>> Well, they can also 'git revert' this patch. If somebody really cares
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>> I think they should shout now and provide a better patch, otherwise
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>> this one should be merged.
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>
>
> On the other hand, having the code there as it currently stands is not
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> harmful in any way, so leaving it there is just as easy.
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>
It makes the code less understandable. I'm not sure about linux's
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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.
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?
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