Subject: Re: [PATCHv3 4/6] iommu/arm-smmu-qcom: Request direct mapping for modem device

From: Sai Prakash Ranjan <[email-masked]>
Date: Mon, 20 Apr 2020 23:40:42 +0530

Hi Robin,

On 2020-04-20 22:39, Robin Murphy wrote:
> On 2020-04-20 5:42 pm, Sai Prakash Ranjan wrote:
>> From: Sibi Sankar <[email-masked]>
>> 
>> Request direct mapping for modem on platforms which don't have 
>> TrustZone
>> (which programs the modem SIDs) to prevent the following global faults 
>> seen
>> on Cheza/Trogdor:
> 
> Not strictly true - it's patch #6/6 that prevents *those* faults (and
> these days the driver should be reporting unmatched streams a little
> more helpfully). This change would resolve the context faults and/or
> weird memory corruption that might result from applying patch #6 alone
> - this is the crazy thing where transactions sometimes go directly to
> DRAM round the side of the SMMU so we can never safely remap anything,
> right?
> 

True this doesnt prevent global faults, the fault details should go to 
patch6.
I'll update the commit msg something like below:

The Q6 modem sub-system has direct access to DDR through memnoc.
Also SMMU is not expected to provide access control/translation for 
these SIDs
(sandboxing of the modem is achieved through XPUs engaged using SMC 
calls).

Thanks,
Sai

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