linux-kernel - Re: [PATCH 2/2] MIPS: CPS: Copy EVA configuration when starting secondary VPs.

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Date:	Wed, 18 May 2016 16:39:12 +0100
From:	Matt Redfearn <matt.redfearn@...tec.com>
To:	Paul Burton <paul.burton@...tec.com>
CC:	Ralf Baechle <ralf@...ux-mips.org>, <linux-mips@...ux-mips.org>,
	<linux-kernel@...r.kernel.org>,
	Markos Chandras <markos.chandras@...tec.com>
Subject: Re: [PATCH 2/2] MIPS: CPS: Copy EVA configuration when starting
 secondary VPs.



On 18/05/16 16:04, Paul Burton wrote:
> On Wed, May 18, 2016 at 03:45:22PM +0100, Matt Redfearn wrote:
>> When starting secondary VPEs which support EVA and the SegCtl registers,
>> copy the memory segmentation configuration from the running VPE to ensure
>> that all VPEs in the core have a consitent virtual memory map.
>>
>> The EVA configuration of secondary cores is dealt with when starting the
>> core via the CM.
>>
>> Signed-off-by: Matt Redfearn <matt.redfearn@...tec.com>
>> ---
>>
>>   arch/mips/kernel/cps-vec.S | 16 ++++++++++++++++
>>   1 file changed, 16 insertions(+)
>>
>> diff --git a/arch/mips/kernel/cps-vec.S b/arch/mips/kernel/cps-vec.S
>> index ac81edd44563..07b3274c8ae1 100644
>> --- a/arch/mips/kernel/cps-vec.S
>> +++ b/arch/mips/kernel/cps-vec.S
>> @@ -431,6 +431,22 @@ LEAF(mips_cps_boot_vpes)
>>   	mfc0	t0, CP0_CONFIG
>>   	mttc0	t0, CP0_CONFIG
>>   
>> +	/* Copy the EVA config from this VPE if the CPU supports it */
>> +	mfc0	t0, CP0_CONFIG, 1
>> +	bgez	t0, 1f
>> +	 mfc0	t0, CP0_CONFIG, 2
>> +	bgez	t0, 1f
>> +	 mfc0	t0, CP0_CONFIG, 3
>> +	and	t0, t0, MIPS_CONF3_SC
>> +	beqz	t0, 1f
>> +	 nop
> Hi Matt,
>
> The checks here aren't *quite* right since they do the mfc0 of the next
> register in the delay slot which will happen even if the M bit of the
> preceeding register wasn't set. There are other cases in cps-vec.S where
> I've made that mistake... Luckily, in this particular case, we know that
> we have MT ASE support which means we know that Config3 exists. So I
> think you can just remove the checks of Config1.M & Config2.M and just
> read Config3 straight away.
Good point - thanks Paul :-)

Matt
>
> Thanks,
>      Paul
>
>> +	mfc0    t0, CP0_SEGCTL0
>> +	mttc0	t0, CP0_SEGCTL0
>> +	mfc0    t0, CP0_SEGCTL1
>> +	mttc0	t0, CP0_SEGCTL1
>> +	mfc0    t0, CP0_SEGCTL2
>> +	mttc0	t0, CP0_SEGCTL2
>> +1:
>>   	/* Ensure no software interrupts are pending */
>>   	mttc0	zero, CP0_CAUSE
>>   	mttc0	zero, CP0_STATUS
>> -- 
>> 2.5.0
>>