linux-kernel - Re: [PATCH] Revert "MIPS: mm: tlbex: Use cpu_has_mips_r2_exec

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Date:	Wed, 11 Mar 2015 09:51:20 -0700
From:	David Daney <ddaney.cavm@...il.com>
To:	Markos Chandras <Markos.Chandras@...tec.com>, ralf@...ux-mips.org
CC:	linux-mips@...ux-mips.org, linux-kernel@...r.kernel.org,
	Leonid Yegoshin <Leonid.Yegoshin@...tec.com>,
	David Daney <david.daney@...ium.com>
Subject: Re: [PATCH] Revert "MIPS: mm: tlbex: Use cpu_has_mips_r2_exec_hazard
 for the EHB instruction"

On 03/11/2015 01:28 AM, Markos Chandras wrote:
> On 02/23/2015 10:52 PM, David Daney wrote:
>> From: David Daney <david.daney@...ium.com>
>>
>> This reverts commit 77f3ee59ee7cfe19e0ee48d9a990c7967fbfcbed.
>>
>> There are two problems:
>>
>> 1) It breaks OCTEON, which will now crash in early boot with:
>>
>>    Kernel panic - not syncing: No TLB refill handler yet (CPU type: 80)
>>
>> 2) The logic is broken.
>>
>> The meaning of cpu_has_mips_r2_exec_hazard is that the EHB instruction
>> is required.  The offending patch attempts (and fails) to change the
>> meaning to be that EHB is part of the ISA.
>>
>> Signed-off-by: David Daney <david.daney@...ium.com>
>> ---
> Hi,
>
> First of all sorry about the octeon breakage.
>
> However, whilst this patch will fix Octeon it will break R6
>

But breaking R6 is not a regression, breaking OCTEON is.  For new code, 
there is this bit of asymmetry.

> Can we please consider another patch that will simply use
> cpu_has_mips_r2_r6 instead of cpu_has_mips_r2 so both will work in 4.0?
>

If you have a patch that fixes the problem properly, please post it for 
consideration.

Thanks,
David Daney




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