Re: [PATCH 06/10] ARC: [plat-eznps] Fix TLB Errata

From	Vineet Gupta <Vineet.Gupta1@synopsys.com>
Newsgroups	linux.kernel
Subject	Re: [PATCH 06/10] ARC: [plat-eznps] Fix TLB Errata
Date	2017-06-01 23:20 +0200
Message-ID	<tNFFD-84v-9@gated-at.bofh.it> (permalink)
References	<tKQQV-2dF-7@gated-at.bofh.it> <tKQQW-2dF-25@gated-at.bofh.it> <tKYOu-7pA-7@gated-at.bofh.it>
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On 05/25/2017 04:00 AM, Alexey Brodkin wrote:
> Hi Noam,
> 
> On Thu, 2017-05-25 at 05:34 +0300, Noam Camus wrote:
>> From: Noam Camus <noamca@mellanox.com>
>>
>> Due to a HW bug in NPS400 we get from time to time false TLB miss.
>> Workaround this by validating each miss.
>>
>> Signed-off-by: Noam Camus <noamca@mellanox.com>
>> ---
>>   arch/arc/mm/tlbex.S |   10 ++++++++++
>>   1 files changed, 10 insertions(+), 0 deletions(-)
>>
>> diff --git a/arch/arc/mm/tlbex.S b/arch/arc/mm/tlbex.S
>> index b30e4e3..1d48723 100644
>> --- a/arch/arc/mm/tlbex.S
>> +++ b/arch/arc/mm/tlbex.S
>> @@ -274,6 +274,13 @@ ex_saved_reg1:
>>   .macro COMMIT_ENTRY_TO_MMU
>>   #if (CONFIG_ARC_MMU_VER < 4)
>>   
>> +#ifdef CONFIG_EZNPS_MTM_EXT
>> +	/* verify if entry for this vaddr+ASID already exists */
>> +	sr    TLBProbe, [ARC_REG_TLBCOMMAND]
>> +	lr    r0, [ARC_REG_TLBINDEX]
>> +	bbit0 r0, 31, 88f
>> +#endif
> 
> That's funny. I think we used to have something like that in the past.

Not here as this is fast path TLB refill handler and landign here implies entry 
was *not* present, unless there's a hardware bug, hence this patch.

Perhaps you are remembering the slow path TLB update code (tlb.c) which has always 
had this - as mm code can call update_mmu_cache() in various cases and in soem of 
those, the entry can be already present so for ARC700 cores we need to ensure that 
dups are not inserted !

>>   	/* Get free TLB slot: Set = computed from vaddr, way = random */
>>   	sr  TLBGetIndex, [ARC_REG_TLBCOMMAND]
>>   
>> @@ -287,6 +294,9 @@ ex_saved_reg1:
>>   #else
>>   	sr TLBInsertEntry, [ARC_REG_TLBCOMMAND]
>>   #endif
>> +#ifdef CONFIG_EZNPS_MTM_EXT
>> +88:
>> +#endif
> 
> Not sure if label itself required wrapping in ifdefs. It just makes code bulkier
> and harder to read.

I agree !

FWIW, after this patch, COMMIT_ENTRY_TO_MMU is totally unreadable - perhaps one of 
us needs to break it up into MMU ver specific implementations. But at any rate 
that can be after this patch.

Thread

[PATCH 00/10] ARC plat-eznps upstream cont. Noam Camus <noamca@mellanox.com> - 2017-05-25 04:40 +0200
  [PATCH 02/10] ARC: send ipi to all cpus sharing task mm in case of page fault Noam Camus <noamca@mellanox.com> - 2017-05-25 04:40 +0200
    Re: [PATCH 02/10] ARC: send ipi to all cpus sharing task mm in case  of page fault Alexey Brodkin <Alexey.Brodkin@synopsys.com> - 2017-05-25 13:40 +0200
  [PATCH 08/10] ARC: [plat-eznps] spinlock aware for MTM Noam Camus <noamca@mellanox.com> - 2017-05-25 04:40 +0200
  [PATCH 06/10] ARC: [plat-eznps] Fix TLB Errata Noam Camus <noamca@mellanox.com> - 2017-05-25 04:40 +0200
    Re: [PATCH 06/10] ARC: [plat-eznps] Fix TLB Errata Alexey Brodkin <Alexey.Brodkin@synopsys.com> - 2017-05-25 13:10 +0200
      RE: [PATCH 06/10] ARC: [plat-eznps] Fix TLB Errata Noam Camus <noamca@mellanox.com> - 2017-05-25 13:20 +0200
      Re: [PATCH 06/10] ARC: [plat-eznps] Fix TLB Errata Vineet Gupta <Vineet.Gupta1@synopsys.com> - 2017-06-01 23:20 +0200
  [PATCH 10/10] ARC: [plat-eznps] Handle memory error as an exception Noam Camus <noamca@mellanox.com> - 2017-05-25 04:40 +0200
    Re: [PATCH 10/10] ARC: [plat-eznps] Handle memory error as an  exception Alexey Brodkin <Alexey.Brodkin@synopsys.com> - 2017-05-25 13:20 +0200
      RE: [PATCH 10/10] ARC: [plat-eznps] Handle memory error as an  exception Noam Camus <noamca@mellanox.com> - 2017-05-25 13:30 +0200
        Re: [PATCH 10/10] ARC: [plat-eznps] Handle memory error as an  exception Alexey Brodkin <Alexey.Brodkin@synopsys.com> - 2017-05-25 13:40 +0200
          RE: [PATCH 10/10] ARC: [plat-eznps] Handle memory error as an  exception Noam Camus <noamca@mellanox.com> - 2017-05-25 14:10 +0200
            Re: [PATCH 10/10] ARC: [plat-eznps] Handle memory error as an  exception Alexey Brodkin <Alexey.Brodkin@synopsys.com> - 2017-05-25 14:10 +0200
          Re: [PATCH 10/10] ARC: [plat-eznps] Handle memory error as an  exception Vineet Gupta <Vineet.Gupta1@synopsys.com> - 2017-06-07 00:00 +0200
  [PATCH 04/10] ARC: typos fix in kernel/entry-compact.S Noam Camus <noamca@mellanox.com> - 2017-05-25 04:40 +0200
    Re: [PATCH 04/10] ARC: typos fix in kernel/entry-compact.S Alexey Brodkin <Alexey.Brodkin@synopsys.com> - 2017-05-25 13:10 +0200

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