linux-kernel - Re: [PATCH 8/9] dt-bindings: reserved-memory: MediaTek: Add reserved memory for SVP

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Message-ID: <c62a7ed8-d80a-3a82-040a-d4c74a71285a@linaro.org>
Date:   Tue, 12 Sep 2023 10:28:35 +0200
From:   Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To:     Yong Wu (吴勇) <Yong.Wu@...iatek.com>,
        "robh@...nel.org" <robh@...nel.org>
Cc:     "sumit.semwal@...aro.org" <sumit.semwal@...aro.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-mediatek@...ts.infradead.org" 
        <linux-mediatek@...ts.infradead.org>,
        "jstultz@...gle.com" <jstultz@...gle.com>,
        "linaro-mm-sig@...ts.linaro.org" <linaro-mm-sig@...ts.linaro.org>,
        "christian.koenig@....com" <christian.koenig@....com>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        Jianjiao Zeng (曾健姣) 
        <Jianjiao.Zeng@...iatek.com>,
        "linux-media@...r.kernel.org" <linux-media@...r.kernel.org>,
        Kuohong Wang (王國鴻) 
        <kuohong.wang@...iatek.com>,
        "Brian.Starkey@....com" <Brian.Starkey@....com>,
        "conor+dt@...nel.org" <conor+dt@...nel.org>,
        "benjamin.gaignard@...labora.com" <benjamin.gaignard@...labora.com>,
        "tjmercier@...gle.com" <tjmercier@...gle.com>,
        "krzysztof.kozlowski+dt@...aro.org" 
        <krzysztof.kozlowski+dt@...aro.org>,
        "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
        "matthias.bgg@...il.com" <matthias.bgg@...il.com>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "angelogioacchino.delregno@...labora.com" 
        <angelogioacchino.delregno@...labora.com>
Subject: Re: [PATCH 8/9] dt-bindings: reserved-memory: MediaTek: Add reserved
 memory for SVP

On 12/09/2023 08:16, Yong Wu (吴勇) wrote:
> Hi Rob,
> 
> Thanks for your review.
> 
> On Mon, 2023-09-11 at 10:44 -0500, Rob Herring wrote:
>>  	 
>> External email : Please do not click links or open attachments until
>> you have verified the sender or the content.
>>  On Mon, Sep 11, 2023 at 10:30:37AM +0800, Yong Wu wrote:
>>> This adds the binding for describing a CMA memory for MediaTek
>> SVP(Secure
>>> Video Path).
>>
>> CMA is a Linux thing. How is this related to CMA?
> 
>>>
>>> Signed-off-by: Yong Wu <yong.wu@...iatek.com>
>>> ---
>>>  .../mediatek,secure_cma_chunkmem.yaml         | 42
>> +++++++++++++++++++
>>>  1 file changed, 42 insertions(+)
>>>  create mode 100644 Documentation/devicetree/bindings/reserved-
>> memory/mediatek,secure_cma_chunkmem.yaml
>>>
>>> diff --git a/Documentation/devicetree/bindings/reserved-
>> memory/mediatek,secure_cma_chunkmem.yaml
>> b/Documentation/devicetree/bindings/reserved-
>> memory/mediatek,secure_cma_chunkmem.yaml
>>> new file mode 100644
>>> index 000000000000..cc10e00d35c4
>>> --- /dev/null
>>> +++ b/Documentation/devicetree/bindings/reserved-
>> memory/mediatek,secure_cma_chunkmem.yaml
>>> @@ -0,0 +1,42 @@
>>> +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
>>> +%YAML 1.2
>>> +---
>>> +$id: 
>> http://devicetree.org/schemas/reserved-memory/mediatek,secure_cma_chunkmem.yaml#
>>> +$schema: http://devicetree.org/meta-schemas/core.yaml#
>>> +
>>> +title: MediaTek Secure Video Path Reserved Memory
>>
>> What makes this specific to Mediatek? Secure video path is fairly 
>> common, right?
> 
> Here we just reserve a buffer and would like to create a dma-buf secure
> heap for SVP, then the secure engines(Vcodec and DRM) could prepare
> secure buffer through it.
>  
> But the heap driver is pure SW driver, it is not platform device and

All drivers are pure SW.

> we don't have a corresponding HW unit for it. Thus I don't think I
> could create a platform dtsi node and use "memory-region" pointer to
> the region. I used RESERVEDMEM_OF_DECLARE currently(The code is in 
> [9/9]). Sorry if this is not right.

If this is not for any hardware and you already understand this (since
you cannot use other bindings) then you cannot have custom bindings for
it either.

> 
> Then in our usage case, is there some similar method to do this? or
> any other suggestion?

Don't stuff software into DTS.

Best regards,
Krzysztof