linux-kernel - Re: [PATCH v6 2/9] doc: DT: venus: binding document for Qualcomm video driver

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Message-ID: <CAL_JsqJ0+YEcw1-DgWpHgdDe4zfppNnpLt6XY=CGnMYwu8ALhw@mail.gmail.com>
Date:   Wed, 22 Feb 2017 08:17:19 -0600
From:   Rob Herring <robh@...nel.org>
To:     Stanimir Varbanov <stanimir.varbanov@...aro.org>
Cc:     Mauro Carvalho Chehab <mchehab@...nel.org>,
        Hans Verkuil <hverkuil@...all.nl>,
        Andy Gross <andy.gross@...aro.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Stephen Boyd <sboyd@...eaurora.org>,
        Srinivas Kandagatla <srinivas.kandagatla@...aro.org>,
        "linux-media@...r.kernel.org" <linux-media@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        linux-arm-msm <linux-arm-msm@...r.kernel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>
Subject: Re: [PATCH v6 2/9] doc: DT: venus: binding document for Qualcomm
 video driver

On Wed, Feb 22, 2017 at 3:25 AM, Stanimir Varbanov
<stanimir.varbanov@...aro.org> wrote:
> Hi Rob,
>
> On 02/22/2017 02:09 AM, Rob Herring wrote:
>> On Tue, Feb 07, 2017 at 03:10:17PM +0200, Stanimir Varbanov wrote:
>>> Add binding document for Venus video encoder/decoder driver
>>>
>>> Cc: Rob Herring <robh+dt@...nel.org>
>>> Cc: devicetree@...r.kernel.org
>>> Signed-off-by: Stanimir Varbanov <stanimir.varbanov@...aro.org>
>>> ---
>>> Changes since previous v5:
>>>  * dropped rproc phandle (remoteproc is not used anymore)
>>>  * added subnodes paragraph with descrition of three subnodes:
>>>     - video-decoder and video-encoder - describes decoder (core0) and
>>>     encoder (core1) power-domains and clocks (applicable for msm8996
>>>     Venus core).
>>>     - video-firmware - needed to get reserved memory region where the
>>>     firmware is stored.
>>>
>>>  .../devicetree/bindings/media/qcom,venus.txt       | 112 +++++++++++++++++++++
>>>  1 file changed, 112 insertions(+)
>>>  create mode 100644 Documentation/devicetree/bindings/media/qcom,venus.txt
>>>
>>> diff --git a/Documentation/devicetree/bindings/media/qcom,venus.txt b/Documentation/devicetree/bindings/media/qcom,venus.txt
>>> new file mode 100644
>>> index 000000000000..4427af3ca5a5
>>> --- /dev/null
>>> +++ b/Documentation/devicetree/bindings/media/qcom,venus.txt
>>> @@ -0,0 +1,112 @@
>>
>> [...]
>>
>>> +* Subnodes
>>> +The Venus node must contain three subnodes representing video-decoder,
>>> +video-encoder and video-firmware.
>>
>> [...]
>>
>>> +The video-firmware subnode should contain:
>>> +
>>> +- memory-region:
>>> +    Usage: required
>>> +    Value type: <phandle>
>>> +    Definition: reference to the reserved-memory for the memory region
>>> +
>>> +* An Example
>>> +    video-codec@...0000 {
>>> +            compatible = "qcom,msm8916-venus";
>>> +            reg = <0x01d00000 0xff000>;
>>> +            interrupts = <GIC_SPI 44 IRQ_TYPE_LEVEL_HIGH>;
>>> +            clocks = <&gcc GCC_VENUS0_VCODEC0_CLK>,
>>> +                     <&gcc GCC_VENUS0_AHB_CLK>,
>>> +                     <&gcc GCC_VENUS0_AXI_CLK>;
>>> +            clock-names = "core", "iface", "bus";
>>> +            power-domains = <&gcc VENUS_GDSC>;
>>> +            iommus = <&apps_iommu 5>;
>>> +
>>> +            video-decoder {
>>> +                    compatible = "venus-decoder";
>>> +                    clocks = <&mmcc VIDEO_SUBCORE0_CLK>;
>>> +                    clock-names = "core";
>>> +                    power-domains = <&mmcc VENUS_CORE0_GDSC>;
>>> +            };
>>> +
>>> +            video-encoder {
>>> +                    compatible = "venus-encoder";
>>> +                    clocks = <&mmcc VIDEO_SUBCORE1_CLK>;
>>> +                    clock-names = "core";
>>> +                    power-domains = <&mmcc VENUS_CORE1_GDSC>;
>>> +            };
>>> +
>>> +            video-firmware {
>>> +                    memory-region = <&venus_mem>;
>>
>> Why does this need to be a sub node?
>
> Because firmware reserved memory region must have separate struct
> device, otherwise allocating video buffers (and map them through iommu)
> for video-codec will fail because dma_alloc_coherent trying to allocate
> from per-device coherent area.

Why can't the struct device be the video-codec device? Looking at the
code, I don't see why you need the 2nd struct device.

In any case, this is letting the driver design the binding which is
wrong. From a binding perspective, there's no reason to have this
node.

Rob