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Message-ID: <ad9d2e4f-1d60-15e7-dc2d-e7e32b0ec855@linaro.org>
Date: Fri, 18 Nov 2022 14:30:23 +0100
From: neil.armstrong@...aro.org
To: Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>,
Bjorn Andersson <andersson@...nel.org>,
Konrad Dybcio <konrad.dybcio@...ainline.org>,
Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
Rob Herring <robh+dt@...nel.org>,
Andy Gross <agross@...nel.org>,
Frank Rowand <frowand.list@...il.com>
Cc: linux-kernel@...r.kernel.org, linux-arm-msm@...r.kernel.org,
devicetree@...r.kernel.org
Subject: Re: [PATCH 1/2] dt-bindings: reserved-memory: document Qualcomm MPSS
DSM memory
On 18/11/2022 11:45, Krzysztof Kozlowski wrote:
> On 17/11/2022 10:47, Neil Armstrong wrote:
>>>
>>>> +
>>>> +properties:
>>>> + compatible:
>>>> + const: qcom,mpss-dsm-mem
>>>
>>> Why do we need dedicated binding and compatible for it instead of using
>>> memory-region phandle in the device?
>>
>> So like rmtfs, this memory zone is shared between APPS and the MPSS subsystem.
>>
>> Like rmtfs it makes no sense to link it to the MPSS PAS, since it's only a launcher,
>> it doesn't represent the MPSS subsystem.
>
> This also does not represent a device. Memory region is not a device, so
> this is as well not correct representation of hardware.
I never used the term device so far, but a shared memory region with a platform
specific process to share the region between subsystems.
>
>>
>> In the PAS startup process, the resources are released from APPS once the MPSS subsystem
>> is running, which is not the case with the MPSS DSM where it must be shared during the whole
>> lifetime of the system.
>
> I don't think that PAS releases the region. I checked the
> qcom_q6v5_pas.c and there is only ioremap. The device stays loaded thus
> the memory stays mapped.
Yes PAS does release the firmware region when the firmware is started,
qcom_scm_pas_metadata_release() does that.
>
> We have already three of such "memory region devices" and we keep
> growing it. It's not scalable.
If we want to properly describe this, we must then represent the MPSS subsystem
and associate this memory region.
>
> Best regards,
> Krzysztof
Thanks,
Neil
>
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