linux-kernel - Re: [PATCH v2 0/6] Add support for Translation Buffer Units

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Message-ID: <47f40099-4215-4c9e-9b7a-c5b981abc589@quicinc.com>
Date:   Thu, 30 Nov 2023 17:19:14 +0200
From:   Georgi Djakov <quic_c_gdjako@...cinc.com>
To:     Bryan O'Donoghue <bryan.odonoghue@...aro.org>,
        <robh+dt@...nel.org>, <krzysztof.kozlowski+dt@...aro.org>,
        <conor+dt@...nel.org>, <will@...nel.org>, <robin.murphy@....com>,
        <joro@...tes.org>
CC:     <devicetree@...r.kernel.org>, <andersson@...nel.org>,
        <konrad.dybcio@...aro.org>, <linux-arm-kernel@...ts.infradead.org>,
        <iommu@...ts.linux.dev>, <linux-kernel@...r.kernel.org>,
        <linux-arm-msm@...r.kernel.org>, <quic_cgoldswo@...cinc.com>,
        <quic_sukadev@...cinc.com>, <quic_pdaly@...cinc.com>,
        <quic_sudaraja@...cinc.com>, <djakov@...nel.org>
Subject: Re: [PATCH v2 0/6] Add support for Translation Buffer Units

On 11/18/2023 1:21 PM, Bryan O'Donoghue wrote:
> On 18/11/2023 04:27, Georgi Djakov wrote:
>> The TCUs (Translation Control Units) and TBUs (Translation Buffer
>> Units) are key components of the MMU-500. Multiple TBUs are connected
>> to a single TCU over an interconnect. Each TBU contains a TLB that
>> caches page tables. The MMU-500 implements a TBU for each connected
>> master, and the TBU is designed, so that it is local to the master.
>>
>> The Qualcomm SDM845 platform has an implementation of the SMMU-500,
>> that has multiple TBUs. A DT schema is added to describe the resources
>> for each TBU (register space, power-domains, interconnects and clocks).
>>
>> The TBU driver will manage the resources and allow the system to
>> operate the TBUs during a context fault to obtain details by doing
>> s1 inv, software + hardware page table walks etc. This is implemented
>> with ATOS/eCATs as the ATS feature is not supported. Being able to
>> query the TBUs is useful for debugging various hardware/software
>> issues on these platforms.
>>
>> v2:
>> - Improve DT binding description, add full example. (Konrad)
>> - Drop Qcom specific stuff from the generic binding. (Rob)
>> - Unconditionally try to populate subnodes. (Konrad)
>> - Improve TBU driver commit text, remove memory barriers. (Bjorn)
>> - Move TBU stuff into separate file. Make the driver builtin.
>> - TODO: Evaluate whether to keep TBU support as a separate driver
>>    or just instantiate things from qcom_smmu_impl_init()
>>
>> v1: https://lore.kernel.org/r/20231019021923.13939-1-quic_c_gdjako@quicinc.com
> 
> What is your suggested way to test this series ?

Hi Bryan,

Just break some driver to initiate a memory transaction with no valid context. I used venus for that. Or the simplest would be to just specify an invalid stream ID in DT for some device.

Thanks,
Georgi