linux-mips
[Top] [All Lists]

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, 24 Dec 2010 06:53:46 -0800
Cc: STUART VENTERS <stuart.venters@adtran.com>, "Anoop P.A." <Anoop_P.A@pmc-sierra.com>, linux-mips@linux-mips.org
Domainkey-signature: a=rsa-sha1; q=dns; c=nofws; s=default; d=paralogos.com; h=Received:Message-ID:Date:From:User-Agent:MIME-Version:To:CC:Subject:References:In-Reply-To:Content-Type:X-Source:X-Source-Args:X-Source-Dir; b=PcPMLr8jqJhaYsVWgBIpjrvP8ufmMWLYnc04sq2rNTFRqg9jot3ZTZqlNfOGl2vrjjYXCRbWYgNV9h/31TpIbLn1LTIinYBWwLW7QKipou1sj3fDnxNl6YQZN+Wr4WnZ;
In-reply-to: <1293201545.27661.55.camel@paanoop1-desktop>
Original-recipient: rfc822;linux-mips@linux-mips.org
References: <8F242B230AD6474C8E7815DE0B4982D7179FB88D@EXV1.corp.adtran.com> <4D1492E0.5090407@paralogos.com> <1293201545.27661.55.camel@paanoop1-desktop>
Sender: linux-mips-bounce@linux-mips.org
User-agent: Mozilla/5.0 (Macintosh; U; Intel Mac OS X 10.5; en-US; rv:1.9.2.13) Gecko/20101207 Thunderbird/3.1.7
Excellent! Now, does the attached patch (relative to 2.6.37.11) also fix things, while preserving the other fixes and performance enhancements?

/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






Attachment: smtc_stackframe.h.patch
Description: Text document

<Prev in Thread] Current Thread [Next in Thread>