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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: Fri, 07 Jan 2011 10:46:24 -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 01/06/11 23:56, Anoop P A wrote:
On Thu, 2011-01-06 at 15:31 -0800, Kevin D. Kissell wrote:
I'm sure I've said this before, and it's in various comments in the SMTC
code, but...
As an aside to this conversation, would it be possible to create a
Documentation/mips/SMTC.txt file that would actually propagate
upstream, so that I'd stop being the sole repository of SMTC folklore?
I only maintain it as a hobby.
Ok. Well thanks much for your detailed explanation. Well I hope I found
the root cause . smtc_clockevent_init() was overriding irq_hwmask even
if are using platform specific get_c0_compare_int. With following patch
everything seems to be working for me.
------------------------------------------------------------------------
diff --git a/arch/mips/kernel/cevt-smtc.c b/arch/mips/kernel/cevt-smtc.c
index 2e72d30..a25fc59 100644
--- a/arch/mips/kernel/cevt-smtc.c
+++ b/arch/mips/kernel/cevt-smtc.c
@@ -310,9 +310,14 @@ int __cpuinit smtc_clockevent_init(void)
                return 0;
        /*
         * And we need the hwmask associated with the c0_compare
-        * vector to be initialized.
+        * vector to be initialized. However incase of platform
+        * specific get_co_compare_int, don't override irq_hwmask
+        * expect platform code to set a valid mask value.
         */
-       irq_hwmask[irq] = (0x100<<  cp0_compare_irq);
+
+       if (!get_c0_compare_int)
+               irq_hwmask[irq] = (0x100<<  cp0_compare_irq);
+
        if (cp0_timer_irq_installed)
                return 0;
-----------------------------------------------------------------------
I'm still not clear on one point that, to me, is pretty important when
engineering a fix here.  Are you, in fact, using the Count/Compare
interrupt system, but having the externalization of the compare
interrupt routed back through an intervening interrupt controller,
or is your timer coming from another source?

In the former case, I think you're on the right track as to the
possible cause of a problem, but the fix should actually be simpler
and rather more elegant.  Why can't you simply see to it that
cp0_compare_irq is set to the right value, either at compile time,
or in your earliest platform initialization of the interrupt controller?
That would be a one-line, inline change and spare us another
cryptic conditional.

In the later case, you'll presumably be having lots of other problems,
as cevt-smtc.c is intertwined with cevt-r4k.c and the Count/Compare
paradigm.

            Regards,

            Kevin K.


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