linux-kernel - Re: [RFC PATCH 08/17] powerpc/e500: Remove conditional "lwsync" substitution

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Message-Id: <AC287A9B-0C8B-494E-95CD-A33014AECE22@kernel.crashing.org>
Date:	Thu, 10 Nov 2011 10:42:25 -0600
From:	Kumar Gala <galak@...nel.crashing.org>
To:	Scott Wood <scottwood@...escale.com>
Cc:	Kyle Moffett <Kyle.D.Moffett@...ing.com>,
	<linuxppc-dev@...ts.ozlabs.org>, <linux-kernel@...r.kernel.org>,
	Baruch Siach <baruch@...s.co.il>,
	Timur Tabi <B04825@...escale.com>,
	Paul Gortmaker <paul.gortmaker@...driver.com>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Paul Mackerras <paulus@...ba.org>
Subject: Re: [RFC PATCH 08/17] powerpc/e500: Remove conditional "lwsync" substitution


On Nov 10, 2011, at 10:31 AM, Scott Wood wrote:

> On Thu, Nov 10, 2011 at 07:40:04AM -0600, Kumar Gala wrote:
>> 
>> On Nov 9, 2011, at 6:07 PM, Kyle Moffett wrote:
>> 
>>> As FreeScale e500 systems have different cacheline sizes from e500mc, it
>>> is basically impossible for the kernel to support both in a single
>>> system image at present.
>>> 
>>> Given that one is SPE-float and the other is classic-float, they are not
>>> generally userspace-compatible either.
>>> 
>>> This patch updates the conditional to depend on whether the system is
>>> actually targetting an "e500" or "e500mc" core and entirely removes the
>>> unused sync-to-lwsync-replacement on e500v1/e500v2 systems.
>>> 
>>> Signed-off-by: Kyle Moffett <Kyle.D.Moffett@...ing.com>
>>> ---
>>> arch/powerpc/include/asm/synch.h |   16 ++++------------
>>> 1 files changed, 4 insertions(+), 12 deletions(-)
>> 
>> Nak, we can run an e500mc in a mode that is compatible with e500v1/v2.  I see no reason to change the support we have there.
> 
> What "mode" do you mean?  DCBZ32?  We don't support using that currently,
> and I'd imagine the performance implication would be such that you'd
> never want to do it unless it's the only way to make some piece of legacy
> software work.

Correct, DCBZ32, we've had customers that go down this path.

>> I see no reason to change the support we have there.
> 
> No reason to remove complexity that is not needed, and is not planned to
> be needed?


I'd rather wait for at least 2 years for e500mc devices to have further deployment before we'd remove this.

- k--
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