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Re: SMTC support status in latest git head.

To: "Kevin D. Kissell" <kevink@paralogos.com>
Subject: Re: SMTC support status in latest git head.
From: Anoop P A <anoop.pa@gmail.com>
Date: Fri, 24 Dec 2010 21:32:16 +0530
Cc: STUART VENTERS <stuart.venters@adtran.com>, "Anoop P.A." <Anoop_P.A@pmc-sierra.com>, linux-mips@linux-mips.org
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Sender: linux-mips-bounce@linux-mips.org
On Fri, 2010-12-24 at 06:53 -0800, Kevin D. Kissell wrote:
> Excellent!  Now, does the attached patch (relative to 2.6.37.11) also 
> fix things, while preserving the other fixes and performance enhancements?
> 
I have tested that patch with 2.6.37 branch it well passes calibration
loop but hangs after switching to mips closource

TC 6 going on-line as CPU 6
Brought up 7 CPUs
bio: create slab <bio-0> at 0
SCSI subsystem initialized
Switching to clocksource MIPS

I Presume this is a different issue as restoring older file didn't help
much to get rid of this hang.

diff --git a/arch/mips/include/asm/stackframe.h
b/arch/mips/include/asm/stackframe.h
index 58730c5..7fc9f10 100644
--- a/arch/mips/include/asm/stackframe.h
+++ b/arch/mips/include/asm/stackframe.h
@@ -195,9 +195,9 @@
                 * to cover the pipeline delay.
                 */
                .set    mips32
-               mfc0    v1, CP0_TCSTATUS
+               mfc0    v0, CP0_TCSTATUS
                .set    mips0
-               LONG_S  v1, PT_TCSTATUS(sp)
+               LONG_S  v0, PT_TCSTATUS(sp)
 #endif /* CONFIG_MIPS_MT_SMTC */
                LONG_S  $4, PT_R4(sp)
                LONG_S  $5, PT_R5(sp)


> /K.
> 
> On 12/24/10 6:39 AM, Anoop P A wrote:
> > Hi Kevin, Stuart ,
> >
> > Woohooo You guys spotted !.
> >
> >   http://git.linux-mips.org/?p=linux.git;a=commit;h=d5ec6e3c seems to be
> > the culprit
> >
> > Once I restored previous version of stackframe.h 2.6.33-stable started
> > booting !.
> >
> > Thanks,
> > Anoop
> >
> > On Fri, 2010-12-24 at 04:32 -0800, Kevin D. Kissell wrote:
> >> Thank you, Stuart!  I've spotted some definite breakage to SMTC between
> >> those versions.  In arch/mips/include/asm/stackframe.h, someone moved
> >> the store of the Status register value in SAVE_SOME (line 169 or 204,
> >> depending on the version) from two instructions after the mfc0 to a
> >> point after the #ifdef for SMTC, presumably to get better pipelining of
> >> the register access.  Unfortunately, the v1 register is also used in the
> >> SMTC-specific fragment to save TCStatus, so the Status value gets
> >> clobbered before it gets stored.  This will eventually result in the
> >> Status register getting a TCStatus value, which has some bits on common,
> >> but isn't identical and sooner or later Bad Things will happen.
> >>
> >> I'm a little surprised this wasn't caught by visual inspection of the 
> >> patch.
> >>
> >> Possible solutions would include reverting the store of the CP0_STATUS
> >> value to the block above the #ifdef, or, to retain whatever performance
> >> advantage was obtained by moving the store downward, to use v0/$2
> >> instead of v1/$3, as the staging register for the TCStatus value.  I'd
> >> lean toward the second option, but I'm not in a position to test and
> >> submit a patch just now.
> >>
> >>               Regards,
> >>
> >>               Kevin K.
> >>
> >> On 12/23/10 1:09 PM, STUART VENTERS wrote:
> >>> Kevin,
> >>>
> >>> I'm not sure if it's useful,
> >>>      but finally I got the time to look at the two kernel versions Anoop 
> >>> pointed out.
> >>>       works   2.6.32-stable with patch 804
> >>>       works_not 2.6.33-stable
> >>>
> >>> greping for files with CONFIG_MIPS_MT_SMTC
> >>>      and looking for timer interrupt related stuff found the following 
> >>> differences:
> >>>
> >>>
> >>> arch/mips/include/asm/irq.h
> >>> arch/mips/kernel/irq.c
> >>>     do_IRQ
> >>>
> >>> arch/mips/include/asm/stackframe.h
> >>>     SAVE_SOME SAVE_TEMP get/set_saved_sp
> >>>
> >>> arch/mips/include/asm/time.h
> >>>     clocksource_set_clock
> >>>
> >>> arch/mips/kernel/process.c
> >>>     cpu_idle
> >>>
> >>> arch/mips/kernel/smtc.c
> >>>     __irq_entry
> >>>     ipi_decode
> >>>         SMTC_CLOCK_TICK
> >>>
> >>>
> >>> Enclosed are the two subsets of files for a more expert look.
> >>>
> >>> I'll try to look in more detail after Christmas.
> >>>
> >>>
> >>> Cheers,
> >>>
> >>> Stuart
> >>>
> >>>
> >>>
> >>>
> >
> 



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