Re: [PATCH 1/6] dt-bindings: remoteproc: qcom,pas-common: Introduce iommus and qcom,devmem property

[Shiraz Hashim]

On Thu, Oct 10, 2024 at 09:15:59AM +0200, Krzysztof Kozlowski wrote:
> On 09/10/2024 16:04, Shiraz Hashim wrote:
> > On Mon, Oct 07, 2024 at 06:25:01PM +0200, Dmitry Baryshkov wrote:
> >> On Mon, 7 Oct 2024 at 17:35, Mukesh Ojha <quic_mojha@xxxxxxxxxxx> wrote:
> >>>
> >>> On Sun, Oct 06, 2024 at 10:38:01PM +0300, Dmitry Baryshkov wrote:
> >>>> On Sat, Oct 05, 2024 at 02:53:54AM GMT, Mukesh Ojha wrote:
> >>>>> From: Shiraz Hashim <quic_shashim@xxxxxxxxxxx>
> >>>>>
> >>>>> Qualcomm’s PAS implementation for remote processors only supports a
> >>>>> single stage of IOMMU translation and is presently managed by the
> >>>>> Qualcomm EL2 hypervisor (QHEE) if it is present. In the absence of QHEE,
> >>>>> such as with a KVM hypervisor, IOMMU translations need to be set up by
> >>>>> the KVM host. Remoteproc needs carveout memory region and its resource
> >>>>> (device memory) permissions to be set before it comes up, and this
> >>>>> information is presently available statically with QHEE.
> >>>>>
> >>>>> In the absence of QHEE, the boot firmware needs to overlay this
> >>>>> information based on SoCs running with either QHEE or a KVM hypervisor
> >>>>> (CPUs booted in EL2).
> >>>>>
> >>>>> The qcom,devmem property provides IOMMU devmem translation information
> >>>>> intended for non-QHEE based systems.
> >>>>>
> >>>>> Signed-off-by: Shiraz Hashim <quic_shashim@xxxxxxxxxxx>
> >>>>> Co-Developed-by: Mukesh Ojha <quic_mojha@xxxxxxxxxxx>
> >>>>> Signed-off-by: Mukesh Ojha <quic_mojha@xxxxxxxxxxx>
> >>>>> ---
> >>>>>  .../bindings/remoteproc/qcom,pas-common.yaml  | 42 +++++++++++++++++++
> >>>>>  .../bindings/remoteproc/qcom,sa8775p-pas.yaml | 20 +++++++++
> >>>>>  2 files changed, 62 insertions(+)
> >>>>>
> >>>>> diff --git a/Documentation/devicetree/bindings/remoteproc/qcom,pas-common.yaml b/Documentation/devicetree/bindings/remoteproc/qcom,pas-common.yaml
> >>>>> index 63a82e7a8bf8..068e177ad934 100644
> >>>>> --- a/Documentation/devicetree/bindings/remoteproc/qcom,pas-common.yaml
> >>>>> +++ b/Documentation/devicetree/bindings/remoteproc/qcom,pas-common.yaml
> >>>>> @@ -52,6 +52,48 @@ properties:
> >>>>>      minItems: 1
> >>>>>      maxItems: 3
> >>>>>
> >>>>> +  iommus:
> >>>>> +    maxItems: 1
> >>>>> +
> >>>>> +  qcom,devmem:
> >>>>> +    $ref: /schemas/types.yaml#/definitions/uint32-matrix
> >>>>> +    description:
> >>>>> +      Qualcomm’s PAS implementation for remote processors only supports a
> >>>>> +      single stage of IOMMU translation and is presently managed by the
> >>>>> +      Qualcomm EL2 hypervisor (QHEE) if it is present. In the absence of QHEE,
> >>>>> +      such as with a KVM hypervisor, IOMMU translations need to be set up by
> >>>>> +      the KVM host. Remoteproc might need some device resources and related
> >>>>> +      access permissions to be set before it comes up, and this information is
> >>>>> +      presently available statically with QHEE.
> >>>>> +
> >>>>> +      In the absence of QHEE, the boot firmware needs to overlay this
> >>>>> +      information based on SoCs running with either QHEE or a KVM hypervisor
> >>>>> +      (CPUs booted in EL2).
> >>>>> +
> >>>>> +      The qcom,devmem property provides IOMMU devmem translation information
> >>>>> +      intended for non-QHEE based systems. It is an array of u32 values
> >>>>> +      describing the device memory regions for which IOMMU translations need to
> >>>>> +      be set up before bringing up Remoteproc. This array consists of 4-tuples
> >>>>> +      defining the device address, physical address, size, and attribute flags
> >>>>> +      with which it has to be mapped.
> >>>>
> >>>> I'd expect that this kind of information is hardware-dependent. As such
> >>>> it can go to the driver itself, rather than the device tree. The driver
> >>>> can use compatible string to select the correct table.
> >>>>
> >>>
> >>> IIUC, are you saying that to move this into driver file and override the
> >>> compatible string via overlay ?
> >>
> >> Ideally we should live without compat overrides. On the other hand,
> >> sc7180 and sc7280 provide an example of doing exactly that.
> > 
> > I am not sure if there can arise a case where updated adsp firmware
> > for particular board(s) may require additional access.
> > 
> > Having it in device tree adds a convenience to deal with such
> > variance. 
> > 
> 
> That's a downstream argument... Just look at the downstream DTS.
> Everything, even software properties, can be added to DT, right?

I was thinking this binding is similar to iommu-addresses approach,
however that is under reserved-memory enumerating memory regions.

regards
Shiraz