Re: [PATCH] firmware: qcom: scm: Allow devicetree-less probe

[Elliot Berman <quic_eberman@quicinc.com>]

On Fri, Sep 20, 2024 at 09:45:37PM +0200, Stephan Gerhold wrote:
> On Fri, Sep 20, 2024 at 11:01:40AM -0700, Elliot Berman wrote:
> > Some devicetrees representing Qualcomm Technologies, Inc. SoCs are
> > missing the SCM node. Users of the SCM device assume the device is
> > present and the driver also assumes it has probed. This can lead to
> > unanticipated crashes when there isn't an SCM device. All Qualcomm
> > Technologies, Inc. SoCs use SCM to communicate with firmware, so create
> > the platform device if it's not present in the devicetree.
> > 
> > Tested that SCM node still probes on:
> >  - sm8650-qrd with the SCM DT node still present
> >  - sm845-mtp with the SCM DT node still present
> >  - sm845-mtp with the node removed
> > 
> > Fixes: 449d0d84bcd8 ("firmware: qcom: scm: smc: switch to using the SCM allocator")
> > Reported-by: Rudraksha Gupta <guptarud@gmail.com>
> > Closes: https://lore.kernel.org/lkml/692cfe9a-8c05-4ce4-813e-82b3f310019a@gmail.com/
> > Link: https://lore.kernel.org/all/CAA8EJpqSKbKJ=y0LAigGdj7_uk+5mezDgnzV5XEzwbxRJgpN1w@mail.gmail.com/
> > Suggested-by: Bartosz Golaszewski <brgl@bgdev.pl>
> > Signed-off-by: Elliot Berman <quic_eberman@quicinc.com>
> 
> Do we actually need this patch?
> 
> We have a simple patch already that fixes the reported regression [1].
> 
> And as I explained in my reply to that series [2], the root cause is not
> the lack of /scm node in the DT, but the time when the SCM call is made
> during the kernel boot process. qcom_scm_set_cold_boot_addr() is called
> in arch/arm/mach-qcom/platsmp.c before any drivers bind to devices in
> the DT. We would need an early_initcall() to run early enough before
> initializing SMP, but I haven't found any examples that the
> device/driver model is actually functional at that point.
> 
> I think applying the simple one line fix from Bartosz [1] should be
> sufficient to restore all functionality that worked before the SCM
> allocator changes.

Ah, I had missed seeing [2]! I am happy with Bartosz's existing patch. I
had thought the discussion in [3] was still relevant.

Thanks,
Elliot

> [1]: https://lore.kernel.org/linux-arm-msm/20240911-tzmem-null-ptr-v2-1-7c61b1a1b463@linaro.org/
> [2]: https://lore.kernel.org/linux-arm-msm/ZuhgV1vicIFzPGI-@linaro.org/

[3]: https://lore.kernel.org/all/CAA8EJpqSKbKJ=y0LAigGdj7_uk+5mezDgnzV5XEzwbxRJgpN1w@mail.gmail.com/