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

[Krzysztof Kozlowski <krzk@kernel.org>]

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@quicinc.com> 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@quicinc.com>
>>>>>
>>>>> 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@quicinc.com>
>>>>> Co-Developed-by: Mukesh Ojha <quic_mojha@quicinc.com>
>>>>> Signed-off-by: Mukesh Ojha <quic_mojha@quicinc.com>
>>>>> ---
>>>>>  .../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?

Best regards,
Krzysztof