Re: [PATCH 2/4] dt-bindings: remoteproc: qcom: sc7180: Update memory-region requirements

[Sibi Sankar]

On 12/14/22 01:11, Krzysztof Kozlowski wrote:
> On 13/12/2022 15:07, Sibi Sankar wrote:
> > Update the bindings to reflect the addition of the new modem metadata
> > carveout reference to the memory-region property.
> >
> > Signed-off-by: Sibi Sankar <quic_sibis@xxxxxxxxxxx>
> > ---
> >   .../devicetree/bindings/remoteproc/qcom,sc7180-mss-pil.yaml    | 3 ++-
> >   .../devicetree/bindings/remoteproc/qcom,sc7280-mss-pil.yaml    | 3 ++-
> >   2 files changed, 4 insertions(+), 2 deletions(-)
> >
> > diff --git a/Documentation/devicetree/bindings/remoteproc/qcom,sc7180-mss-pil.yaml b/Documentation/devicetree/bindings/remoteproc/qcom,sc7180-mss-pil.yaml
> > index e4a7da8020f4..b1402bef0ebe 100644
> > --- a/Documentation/devicetree/bindings/remoteproc/qcom,sc7180-mss-pil.yaml
> > +++ b/Documentation/devicetree/bindings/remoteproc/qcom,sc7180-mss-pil.yaml
> > @@ -95,6 +95,7 @@ properties:
> >       items:
> >         - description: MBA reserved region
> >         - description: modem reserved region
> > +      - description: metadata reserved region
>
> Which makes the third item now required, also for all out of tree DTS
> and other users of the bindings. Please write a bit more in commit msg
> why this is necessary (e.g. was it broken before?). I assume the driver
> does not break the ABI?

I'll pad the commit msg with some of the additional info from patch 4.
commit c44094eee32f "arm64: dma: Drop cache invalidation from
arch_dma_prep_coherent()" exposed a bug in the driver affecting SoCs
from msm8996 on wards. The application processor accessing the
dynamically allocated region after giving control to the modem results
in a XPU violation. The recommended fix was to use a no-map carveout
instead and memunmap before giving control to the modem. The future
kernels that are paired with an older dtbs would crash during modem
bootup since we would continue to use dma_alloc_attr. But all the other
combinations (old kernel/new dtb) will continue to work.

- Sibi

> Best regards,
> Krzysztof