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    SubjectRe: [PATCH] arm: remove unused code in delay.S
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    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.

    --
    Felipe Contreras
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