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Re: SMTC support status in latest git head.

To: Anoop P A <anoop.pa@gmail.com>
Subject: Re: SMTC support status in latest git head.
From: "Kevin D. Kissell" <kevink@paralogos.com>
Date: Wed, 05 Jan 2011 11:23:17 -0800
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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On 01/05/11 05:11, Anoop P A wrote:
On Tue, 2011-01-04 at 10:33 -0800, Kevin D. Kissell wrote:
On 01/04/11 09:54, Anoop P A wrote:
On Tue, 2011-01-04 at 09:21 -0800, Kevin D. Kissell wrote:
I'm trying to figure out a reason why your change below should help, and
offhand, modulo tool bugs, I don't see it.  I'm assuming that your diff
below is a diff relative to the pre-patch stackframe.h.   I wouldn't
Yes patch created against stock code .

bless it as an alternative because it moves code and comments
unnecessarily - all you should really have to do is to move the


    190                 mfc0    v1, CP0_STATUS
    191                 LONG_S  $2, PT_R2(sp)

to be just after the #endif /* CONFIG_MIPS_MT_SMTC */ at around line 201.
Actually I just moved code under CONFIG_MIPS_MT_SMTC to previous block
of code ( which store $0 ) . git diff did the rest on behalf of me :)

If moving the save of zero to PT_R0(sp) actually makes a difference,
it's evidence that you've got problems in your toolchain (or, heaven
forbid, your pipeline)!
In previous version of patch usage of V0 was creating issue. I have
verified this with previous version of code ( working code before
David's instruction rearrangement patch.) .
Argh.  It's not very clearly commented, but it looks as if the system
call trap handler has an implicit assumption that v0 has never been
changed by SAVE_SOME, TRACE_IRQS_ON_RELOAD, or STI.  So yeah, moving the
code around to fix the v1 conflict ends up being better than using v0 -
otherwise, we'd need to add a LONG_L v0, PT_R2(sp) somewhere after the
LONG_S v0, PT_TCSTATUS(sp) of the original patch.
Well, Here is the patch.

diff --git a/arch/mips/include/asm/stackframe.h
b/arch/mips/include/asm/stackframe.h
index 58730c5..19418c4 100644
--- a/arch/mips/include/asm/stackframe.h
+++ b/arch/mips/include/asm/stackframe.h
@@ -187,8 +187,6 @@
                 * need it to operate correctly
                 */
                LONG_S  $0, PT_R0(sp)
-               mfc0    v1, CP0_STATUS
-               LONG_S  $2, PT_R2(sp)
  #ifdef CONFIG_MIPS_MT_SMTC
                /*
                 * Ideally, these instructions would be shuffled in
@@ -199,6 +197,8 @@
                .set    mips0
                LONG_S  v1, PT_TCSTATUS(sp)
  #endif /* CONFIG_MIPS_MT_SMTC */
+               mfc0    v1, CP0_STATUS
+               LONG_S  $2, PT_R2(sp)
                LONG_S  $4, PT_R4(sp)
                LONG_S  $5, PT_R5(sp)
                LONG_S  v1, PT_STATUS(sp)

That's exactly what I'd propose as the cleanest minimal fix. I've got a version that also replaces the .set mips32 / .set mips0 with the .set push / .set pop paradigm, which I'd have used in the original code if I'd known at the time about that assembler directive. I'm hoping to be able to test on a Malta/34K reference platform, and make sure there isn't breakage on that platform branch as well, before we commit to the repository.

Your msp_smtc.c file looks plausible on the face of it. The init_secondary function has the quirk that it expects to execute on each "CPU" in numerical order, which is very likely but not guaranteed. It *ought* to be harmless in the rare case where it fails, but the assumption is worth a comment, IMHO.

At this point, there shouldn't be a whole lot of SMTC-specific mystery to get your timer running on the second VPE. You know it's taking interrupts, because of the IPIs getting through, so in principle you just need to run the chain of enables from the clock peripheral itself through the CIC to the CPU core and the IM bits.

It would be really cool if we could get a stable repository branch that boots SMTC out-of-the-box on both Malta and the MSP platform.

            Regards,

            Kevin K.



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