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

[Ashish Mhetre]

On 11/24/2022 5:04 PM, Krzysztof Kozlowski wrote:
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>
> 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