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Subject: Re: [PATCH v1 1/2] iommu/tegra-smmu: Defer attachment of display
 clients
From:   Dmitry Osipenko <digetx@gmail.com>
To:     Thierry Reding <thierry.reding@gmail.com>
Cc:     Joerg Roedel <joro@8bytes.org>,
        Jonathan Hunter <jonathanh@nvidia.com>,
        Krishna Reddy <vdumpa@nvidia.com>,
        Nicolin Chen <nicoleotsuka@gmail.com>,
        Will Deacon <will@kernel.org>,
        iommu@lists.linux-foundation.org, linux-tegra@vger.kernel.org,
        linux-kernel@vger.kernel.org
References: <20210328233256.20494-1-digetx@gmail.com>
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Date:   Fri, 9 Apr 2021 15:55:41 +0300
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08.04.2021 17:07, Dmitry Osipenko пишет:
>> Whatever happened to the idea of creating identity mappings based on the
>> obscure tegra_fb_mem (or whatever it was called) command-line option? Is
>> that command-line not universally passed to the kernel from bootloaders
>> that initialize display?
> This is still a good idea! The command-line isn't universally passed
> just because it's up to a user to override the cmdline and then we get a
> hang (a very slow boot in reality) on T30 since display client takes out
> the whole memory bus with the constant SMMU faults. For example I don't
> have that cmdline option in my current setups.
> 

Thinking a bit more about the identity.. have you consulted with the
memory h/w people about whether it's always safe to enable ASID in a
middle of DMA request?