linux-kernel - Re: [Patch V2] memory: tegra: Remove clients SID override programming

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Date:   Fri, 25 Nov 2022 09:19:49 +0530
From:   Ashish Mhetre <amhetre@...dia.com>
To:     Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>,
        thierry.reding@...il.com, jonathanh@...dia.com,
        dmitry.osipenko@...labora.com, linux-kernel@...r.kernel.org,
        linux-tegra@...r.kernel.org
Subject: Re: [Patch V2] memory: tegra: Remove clients SID override programming


On 11/24/2022 5:04 PM, Krzysztof Kozlowski wrote:
> External email: Use caution opening links or attachments
>
>
> On 24/11/2022 11:20, Ashish Mhetre wrote:
>> On 11/22/2022 4:44 PM, Krzysztof Kozlowski wrote:
>>> External email: Use caution opening links or attachments
>>>
>>>
>>> On 22/11/2022 06:31, Ashish Mhetre wrote:
>>>> On newer Tegra releases, early boot SID override programming and SID
>>>> override programming during resume is handled by bootloader.
>>>> Also, SID override is programmed on-demand during probe_finalize() call
>>>> of IOMMU which is done in tegra186_mc_client_sid_override() in this same
>>>> file. This function does it more correctly by checking if write is
>>>> permitted on SID override register. It also checks if SID override
>>>> register is already written with correct value and skips re-writing it
>>>> in that case.
>>>> Hence, removing the SID override programming of all clients.
>>>>
>>>> Fixes: 393d66fd2cac ("memory: tegra: Implement SID override programming")
>>> I could not get from commit msg what is the bug being fixed. You just
>>> said "more correctly", but usually things are either correct or not.
>>> What are visible effects of the bug?
>>>
>>> Otherwise it sounds more like optimization or a bit better approach, but
>>> not a bugfix.
>>>
>>> Best regards,
>>> Krzysztof
>> Thanks for the review. In the function tegra186_mc_program_sid() which is
>> getting removed, SID override register of all clients is written without
>> checking if secure firmware has allowed write on it or not. If write is
>> disabled by secure firmware then it can lead to errors coming from secure
>> firmware and hang in kernel boot. So, that's a possible bug.
> Please add it to commit msg, because it justifies Fixes tag and probably
> backport.

Sure, I will send V3 with updated commit message. Thank you.

>> Also, it's an optimization over current approach because it saves time by
>> removing re-writing of these SID override registers as in new Tegra releases
>> SID override of all clients is programmed by bootloader. So, MC driver don't
>> need to program them again.
> Best regards,
> Krzysztof
>