linux-hardening - Re: [PATCH v4 08/21] dt-bindings: reserved-memory: Add qcom,ramoops binding

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Date:   Mon, 3 Jul 2023 09:20:35 +0200
From:   Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To:     Mukesh Ojha <quic_mojha@...cinc.com>
Cc:     Rob Herring <robh+dt@...nel.org>, corbet@....net,
        agross@...nel.org, andersson@...nel.org, konrad.dybcio@...aro.org,
        conor+dt@...nel.org, keescook@...omium.org, tony.luck@...el.com,
        gpiccoli@...lia.com, mathieu.poirier@...aro.org,
        catalin.marinas@....com, will@...nel.org, linus.walleij@...aro.org,
        andy.shevchenko@...il.com, linux-doc@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-arm-msm@...r.kernel.org,
        devicetree@...r.kernel.org, linux-hardening@...r.kernel.org,
        linux-remoteproc@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-gpio@...r.kernel.org
Subject: Re: [PATCH v4 08/21] dt-bindings: reserved-memory: Add qcom,ramoops binding

On Mon, 3 Jul 2023 at 08:22, Mukesh Ojha <quic_mojha@...cinc.com> wrote:
> On 7/2/2023 1:42 PM, Krzysztof Kozlowski wrote:
> >>> The big difference is if firmware is not deciding where this log
> >>> lives, then it doesn't need to be in DT. How does anything except the
> >>> kernel that allocates the log find the logs?
> >>
> >> Yes, you are correct, firmware is not deciding where the logs lives
> >> instead here, Kernel has reserved the region where the ramoops region
> >> lives and later with the minidump registration where, physical
> >> address/size/virtual address(for parsing) are passed and that is how
> >> firmware is able to know and dump those region before triggering system
> >> reset.
> >
> > Your explanation does not justify storing all this in DT. Kernel can
> > allocate any memory it wishes, store there logs and pass the address to
> > the firmware. That's it, no need for DT.
>
> If you go through the driver, you will know that what it does, is

We talk about bindings and I should not be forced to look at the
driver to be able to understand them. Bindings should stand on their
own.

> just create platform device for actual ramoops driver to probe and to

Not really justification for Devicetree anyway. Whatever your driver
is doing, is driver's business, not bindings.

> provide this it needs exact set of parameters of input what original
> ramoops DT provides, we need to keep it in DT as maintaining this in
> driver will not scale well with different size/parameter size
> requirement for different targets.

Really? Why? I don't see a problem in scaling. At all.

>
> >
> >>
> >> A part of this registration code you can find in 11/21
> >>
> >>> I'm pretty sure I already said all this before.
> >>
> >> Yes, you said this before but that's the reason i came up with vendor
> >> ramoops instead of changing traditional ramoops binding.
> >
> > That's unexpected conclusion. Adding more bindings is not the answer to
> > comment that it should not be in the DTS in the first place.
>
> Please suggest, what is the other way being above text as requirement..

I do not see any requirement for us there. Forcing me to figure out
how to add non-hardware property to DT is not the way to convince
reviewers. But if you insist - we have ABI for this, called sysfs. If
it is debugging feature, then debugfs.

Best regards,
Krzysztof