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Re: [MIPS] SB1: Build fix: delete initialization of flush_icache_page po

To: Atsushi Nemoto <anemo@mba.ocn.ne.jp>
Subject: Re: [MIPS] SB1: Build fix: delete initialization of flush_icache_page pointer.
From: Ralf Baechle <ralf@linux-mips.org>
Date: Thu, 28 Sep 2006 11:14:48 +0100
Cc: manoje@broadcom.com, linux-mips@linux-mips.org, mark.e.mason@broadcom.com
In-reply-to: <20060928.132712.47915433.nemoto@toshiba-tops.co.jp>
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References: <20060927.235804.95064004.anemo@mba.ocn.ne.jp> <710F16C36810444CA2F5821E5EAB7F230A0E91@NT-SJCA-0752.brcm.ad.broadcom.com> <20060928.132712.47915433.nemoto@toshiba-tops.co.jp>
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On Thu, Sep 28, 2006 at 01:27:12PM +0900, Atsushi Nemoto wrote:
> Date: Thu, 28 Sep 2006 13:27:12 +0900 (JST)
> To:   manoje@broadcom.com
> Cc:   linux-mips@linux-mips.org, ralf@linux-mips.org,
>       mark.e.mason@broadcom.com
> Subject: Re: [MIPS] SB1: Build fix: delete initialization of
>  flush_icache_page pointer.
> From: Atsushi Nemoto <anemo@mba.ocn.ne.jp>
> Content-Type: Text/Plain; charset=us-ascii
> 
> On Wed, 27 Sep 2006 19:17:16 -0700, "Manoj Ekbote" <manoje@broadcom.com> 
> wrote:
> > I added a line that initializes the flush_icache_page pointer in
> > sb1_cache_init.
> > The below method worked. The SMP kernel boots fine now. Removing parts
> > of local_sb1_flush_icache_page doesn't help. It looks like
> > flush_icache_page in mm/memory.c:do_no_page is needed. Removing it will
> > fail the boot process.
> 
> Thank you for testing.
> 
> Now I'm wondering why do_no_page() works on SMP.
> 
>       if (pte_none(*page_table)) {
>               flush_icache_page(vma, new_page);
>               entry = mk_pte(new_page, vma->vm_page_prot);
>               if (write_access)
>                       entry = maybe_mkwrite(pte_mkdirty(entry), vma);
>               set_pte_at(mm, address, page_table, entry);
> ...
>       } else {
>               /* One of our sibling threads was faster, back out. */
>               page_cache_release(new_page);
>               goto unlock;
>       }
> 
>       /* no need to invalidate: a not-present page shouldn't be cached */
>       update_mmu_cache(vma, address, entry);
> 
> Other CPU might be able to load new pte value just after set_ste_at(),
> but dcache is not flushed until update_mmu_cache().  Maybe I missed
> something...
> 
> > I am wondering if people have booted the latest tree on non-Broadcom
> > boards...curious to know if the removal of flush_icache_page has
> > affected them.
> 
> Yes, Ralf and Thiemo said even some SB1 boards can work fine without
> flush_icache_page.

The have to by definition - flush_icache_page is going to go away.

Note the SB1 cache code is a bizarre beast.  It totally avoids Hit-type
cacheops because those used to have problems on early silicon.  So my
favorite solution would be to dump c-sb1.c and deal with any SB1 issues
that may pop up in c-r4k.c.

  Ralf

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