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[PATCH][MIPS] add CP0 hazard to CP0 compare register accesses

To: Ralf Baechle <ralf@linux-mips.org>
Subject: [PATCH][MIPS] add CP0 hazard to CP0 compare register accesses
From: Yoichi Yuasa <yoichi_yuasa@tripeaks.co.jp>
Date: Wed, 19 Mar 2008 16:38:47 +0900
Cc: yoichi_yuasa@tripeaks.co.jp, linux-mips <linux-mips@linux-mips.org>
In-reply-to: <20080318132709.GC11382@linux-mips.org>
Organization: TriPeaks Corporation
Original-recipient: rfc822;linux-mips@linux-mips.org
References: <20080317234740.705a8a34.yoichi_yuasa@tripeaks.co.jp> <20080317161635.GA25549@linux-mips.org> <200803180447.m2I4lJ40005091@po-mbox301.hop.2iij.net> <20080318132709.GC11382@linux-mips.org>
Sender: linux-mips-bounce@linux-mips.org
Hi,

On Tue, 18 Mar 2008 13:27:09 +0000
Ralf Baechle <ralf@linux-mips.org> wrote:

> On Tue, Mar 18, 2008 at 01:47:20PM +0900, Yoichi Yuasa wrote:
> 
> > On Mon, 17 Mar 2008 16:16:35 +0000
> > Ralf Baechle <ralf@linux-mips.org> wrote:
> > 
> > > On Mon, Mar 17, 2008 at 11:47:40PM +0900, Yoichi Yuasa wrote:
> > > 
> > > > VR41xx, CP0 hazard is necessary between read_c0_count() and 
> > > > write_c0_compare().
> > > 
> > > Interesting.  I wonder why you need this patch but nobody else?
> > 
> > Three NOP are necessary on the TB0287(VR4131 board).
> 
> That much was obvious from your patch.  I was more wondering about this
> change:
> 
> -               write_c0_compare(read_c0_count());
> +               c0_timer_ack();
> 
> c0_timer_ack is defined as
> 
> static void c0_timer_ack(void)
> {
>         write_c0_compare(read_c0_compare());
> }
> 
> so your patch does a functional change there - even though it should not
> actually matter.  So I was wondering if for some reason you need that
> change.

OK, update my patch.
Two patches have been brought together in one.

How about this?

VR41xx, CP0 hazard is necessary between read_c0_count() and write_c0_compare()
(or read_c0_cause()).

Signed-off-by: Yoichi Yuasa <yoichi_yuasa@tripeaks.co.jp>

diff -pruN -X /home/yuasa/Memo/dontdiff linux-orig/arch/mips/kernel/cevt-r4k.c 
linux/arch/mips/kernel/cevt-r4k.c
--- linux-orig/arch/mips/kernel/cevt-r4k.c      2008-03-19 11:35:53.017749179 
+0900
+++ linux/arch/mips/kernel/cevt-r4k.c   2008-03-19 16:31:29.617938142 +0900
@@ -186,7 +186,9 @@ static int c0_compare_int_usable(void)
         * IP7 already pending?  Try to clear it by acking the timer.
         */
        if (c0_compare_int_pending()) {
-               write_c0_compare(read_c0_count());
+               cnt = read_c0_count();
+               back_to_back_c0_hazard();
+               write_c0_compare(cnt);
                irq_disable_hazard();
                if (c0_compare_int_pending())
                        return 0;
@@ -205,10 +207,13 @@ static int c0_compare_int_usable(void)
        while ((int)(read_c0_count() - cnt) <= 0)
                ;       /* Wait for expiry  */
 
+       back_to_back_c0_hazard();
        if (!c0_compare_int_pending())
                return 0;
 
-       write_c0_compare(read_c0_count());
+       cnt = read_c0_count();
+       back_to_back_c0_hazard();
+       write_c0_compare(cnt);
        irq_disable_hazard();
        if (c0_compare_int_pending())
                return 0;

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