Re: [Qemu-devel] [PATCH] target-ppc: Eliminate redundant and incorrect function booke206_page_size_to_tlb

[David Gibson <david@gibson.dropbear.id.au>]

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On Mon, Jun 27, 2016 at 10:55:03AM -0500, alarson@ddci.com wrote:
> David Gibson <david@gibson.dropbear.id.au> wrote on 06/27/2016 12:32:13 
> AM:
> 
> > From: David Gibson <david@gibson.dropbear.id.au>
> > To: alarson@ddci.com
> > Cc: agraf@suse.de, qemu-devel@nongnu.org, qemu-ppc@nongnu.org
> > Date: 06/27/2016 12:30 AM
> > Subject: Re: [PATCH] target-ppc: Eliminate redundant and incorrect 
> function booke206_page_size_to_tlb
> > 
> > On Sun, Jun 26, 2016 at 09:38:03PM -0500, alarson@ddci.com wrote:
> > > David Gibson <david@gibson.dropbear.id.au> wrote on 06/26/2016 
> 08:36:52 
> > > PM:
> > > 
> > > > From: David Gibson <david@gibson.dropbear.id.au>
> > > > To: Aaron Larson <alarson@ddci.com>
> > > > Cc: agraf@suse.de, qemu-devel@nongnu.org, qemu-ppc@nongnu.org
> > > > Date: 06/26/2016 08:58 PM
> > > > Subject: Re: [PATCH] target-ppc: Eliminate redundant and incorrect 
> > > function booke206_page_size_to_tlb
> > > > 
> > > > On Fri, Jun 24, 2016 at 12:11:00PM -0700, Aaron Larson wrote:
> > > > > 
> > > > > Eliminate redundant and incorrect booke206_page_size_to_tlb 
> function
> > > > > from ppce500_spin.c in preference to previously existing but newly
> > > > > exported definition from e500.c
> > > > > 
> > > > > Signed-off-by: Aaron Larson <alarson@ddci.com>
> > > > 
> > > > Uh.. sorry.. can you provide a reference explaining why the removed
> > > > version is wrong?  Doesn't this depend on which MMU Architecture
> > > > Version we're emulating?
> > > 
> > > Sure, the code is internally inconsistent (shift assumed didn't match 
> > > shift defined).  I will provide an update commit message, similar to 
> the 
> > > original posting I made a few days ago with the "direction"
> > > corrected.
> > 
> > Right, I can see that the two old versions were different, which was
> > clearly wrong.  What I'm looking for is an explanation of why the one
> > you've picked is the right one, not the other one.
> 
> How's this?
> 
> Eliminate redundant and incorrect booke206_page_size_to_tlb function
> from ppce500_spin.c in preference to previously existing but newly
> exported definition from e500.c
> 
> The booke206_page_size_to_tlb function in e500.c was updated in commit
> 2bd9543cd303d9f6cbd37b7466bb03543035156b to reflect a change in the
> definition of MAS1_TSIZE_SHIFT from 8 (corresponding to a min TLB page
> size of 4kb) to a value of 7 (TLB page size 2k).  The
> booke206_page_size_to_tlb() function defined in ppce500_spin.c was
> never updated to reflect the change in MAS1_TSIZE_SHIFT.

Ah, yes, that looks good.  Except that the convention when citing
other commits is to just use the first 7 characters of the commit id,
but to include the 1 line description.  So:

   ...commit 2bd9543 "ppc: booke206: use MAV=2.0 TSIZE definition, fix
      4G pages" to reflect...

> In http://lists.nongnu.org/archive/html/qemu-ppc/2016-06/msg00533.html,
> Scott Wood suggested this "root cause" explanation:
> 
> SW> The patch that changed MAS1_TSIZE_SHIFT from 8 to 7 was around the
> SW> same time as the patch that added this code, which is probably why
> SW> adjusting it got missed.  Commit 2bd9543cd3 did update the
> SW> equivalent code in ppce500_mpc8544ds.c, which now resides in
> SW> hw/ppc/e500.c and has been changed to not assume a power-of-2
> SW> size.  The ppce500_spin version should be eliminated.
> 

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson

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