linux-kernel - Re: [PATCH 4/4] dt-bindings: firmware: Add Qualcomm UEFI Secure Application client

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Date:   Thu, 28 Jul 2022 17:16:11 +0100
From:   Sudeep Holla <sudeep.holla@....com>
To:     Ard Biesheuvel <ardb@...nel.org>
Cc:     Maximilian Luz <luzmaximilian@...il.com>,
        Ilias Apalodimas <ilias.apalodimas@...aro.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>,
        Sudeep Holla <sudeep.holla@....com>,
        Andy Gross <agross@...nel.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Konrad Dybcio <konrad.dybcio@...ainline.org>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Steev Klimaszewski <steev@...i.org>,
        Shawn Guo <shawn.guo@...aro.org>,
        Cristian Marussi <cristian.marussi@....com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-arm-msm <linux-arm-msm@...r.kernel.org>,
        linux-efi <linux-efi@...r.kernel.org>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 4/4] dt-bindings: firmware: Add Qualcomm UEFI Secure
 Application client

On Thu, Jul 28, 2022 at 08:05:58AM -0700, Ard Biesheuvel wrote:
> On Thu, 28 Jul 2022 at 04:33, Sudeep Holla <sudeep.holla@....com> wrote:
> >
> > On Thu, Jul 28, 2022 at 12:48:19PM +0200, Maximilian Luz wrote:
> >
> > [...]
> >
> > >
> > > I would very much like to avoid the need for special bootloaders. The
> > > devices we're talking about are WoA devices, meaning they _should_
> > > ideally boot just fine with EFI and ACPI.
> > >
> >
> > Completely agreed.
> >
> > > From an end-user perspective, it's annoying enough that we'll have to
> > > stick with DTs for the time being due to the use of PEPs in ACPI.
> >
> > But have we explored or investigated what it takes to rewrite ACPI f/w
> > to just use standard methods ? Does it require more firmware changes or
> > new firmware entities or impossible at any cost ?
> >
> > For me that is more important than just getting this one on DT. Because
> > if you take that path, we will have to keep doing that, with loads of
> > unnecessary drivers if they are not shared with any other SoC with DT
> > support upstream. We might also miss chance to get things added to the ACPI
> > spec as we don't care which means that we never be able to use ACPI on
> > similar future platforms even though they get shipped with ACPI.
> >
> > It will be a loop where we constantly keep converting this ACPI shipped
> > platform into DT upstream. IMHO we don't want to be there.
> >
>
> Supporting these devices in Linux in ACPI mode would involve
> reimplementing the PEP subsystem, and reimplementing PEP drivers for
> all these QCOM peripherals to manage the probing and the power states.
> I don't think this is realistic at all, and a huge waste of
> engineering effort otherwise.
>

I am aware of that and hence I am happy to see these as one off drivers
if needed. But if we don't stop that or keep converting them to DT,
IMO we will be in vicious circle of this conversion and will never be
able to support ACPI natively on these platforms. I know it is huge
effort and not expecting that to be done here, but we need to convey the
message to use ACPI standards or improve it if there is a need. Using
PEP is not helpful to run Linux in the long run. Also we may hit a point
when it may not be trivial to do that ACPI<->DT conversion.

> It is also orthogonal to the discussion, as far as I understand: ACPI
> is not telling the system whether or not these TZ services should be
> used instead of EFI runtime calls.
>

Agreed and I don't want to block any such discussions. Sorry if I derailed
the discussion, that was not my intentions.

--
Regards,
Sudeep