linux-kernel - Re: [PATCH v4 6/8] firmware: qcom: scm: add modparam to control QSEECOM enablement

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Message-ID: <cjinqyqn7qgvdoltoywxa2lq6bjyfrotmon3iv24tqt3bpdlpe@3xb2k42ffegj>
Date: Fri, 27 Jun 2025 02:33:27 +0300
From: Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>
To: Johan Hovold <johan@...nel.org>
Cc: Bjorn Andersson <andersson@...nel.org>,
        Maximilian Luz <luzmaximilian@...il.com>,
        Konrad Dybcio <konradybcio@...nel.org>, Rob Herring <robh@...nel.org>,
        Krzysztof Kozlowski <krzk+dt@...nel.org>,
        Conor Dooley <conor+dt@...nel.org>, Ard Biesheuvel <ardb@...nel.org>,
        Steev Klimaszewski <steev@...i.org>, linux-arm-msm@...r.kernel.org,
        linux-kernel@...r.kernel.org, devicetree@...r.kernel.org,
        linux-efi@...r.kernel.org,
        Dmitry Baryshkov <dmitry.baryshkov@...aro.org>,
        Konrad Dybcio <konrad.dybcio@....qualcomm.com>
Subject: Re: [PATCH v4 6/8] firmware: qcom: scm: add modparam to control
 QSEECOM enablement

On Thu, Jun 26, 2025 at 02:58:52PM +0200, Johan Hovold wrote:
> On Thu, Jun 26, 2025 at 02:08:23PM +0300, Dmitry Baryshkov wrote:
> > On Thu, Jun 26, 2025 at 12:11:20PM +0200, Johan Hovold wrote:
> > > On Wed, Jun 25, 2025 at 01:53:25AM +0300, Dmitry Baryshkov wrote:
> > > > From: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
> > > > 
> > > > In preparation to enabling QSEECOM for the platforms rather than
> > > > individual machines provide a mechanism for the user to override default
> > > > selection. Allow users to use qcom_scm.qseecom modparam.
> > > > 
> > > > Setting it to 'force' will enable QSEECOM even if it disabled or not
> > > > handled by the allowlist.
> > > > 
> > > > Setting it to 'off' will forcibly disable the QSEECOM interface,
> > > > allowing incompatible machines to function.
> > > > 
> > > > Setting it to 'roefivars' will enable the QSEECOM interface, making UEFI
> > > > variables read-only.
> > > > 
> > > > All other values mean 'auto', trusting the allowlist in the module.
> > > 
> > > I don't see the need for this. The kernel should just provide sensible
> > > defaults.
> > 
> > It does provide _defaults_. However with the next commit we mass-enable
> > QSEECOM for SoC families, which includes untested WoA devices. If the
> > user observes a misbehaviour of the UEFI vars or any other
> > QSEECOM-related driver on those platforms, it is much easier to let
> > users test and workaround UEFI misbehaviour.
> 
> You basically know by now which machines supports qseecom and which do
> not, right (e.g. UFS storage means non-persistent EFI vars)?
> 
> And it's a pretty bad user experience to have people trying to write
> efivariables when setting up a machine and then spend hours trying to
> debug why they don't persist after a reboot.
> 
> I don't think that's fair to users.

So, is it a user or a developer, trying to port Linux to a new hardware?
Also, R/O implementation makes it obvious, that the variables do not
persist.

> 
> Let whoever brings up a new machine figure this out. It's just one
> entry, no scaling issues, and we get accurate information (unless
> Qualcomm, who sits on the documentation, is willing to provide it
> upfront).

And that's not really scallable. All other parts of a particular device
are described by the DT only (that's especially true on the PMIC GLINK
machines). If we are to support new laptop in e.g. distro kernel, we
need to provide a DT... and a patch for qcom-scm driver. I'd very much
prefer to do it other way around: provide a DT and patch qcom-scm if the
laptop is any way different from other laptops. E.g. we know that all
X1Elite laptops support R/W EFI variables. Except for X1-CRD, which
deserves an entry in the driver.

-- 
With best wishes
Dmitry