linux-kernel - Re: [PATCH v2 4/8] dt-bindings: serial: Add support for selecting data transfer mode

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Message-ID: <65a880ba-f721-4720-81f7-6891c335f7aa@oss.qualcomm.com>
Date: Mon, 27 Jan 2025 18:50:34 +0100
From: Konrad Dybcio <konrad.dybcio@....qualcomm.com>
To: Krzysztof Kozlowski <krzk@...nel.org>,
        Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
Cc: Viken Dadhaniya <quic_vdadhani@...cinc.com>, andi.shyti@...nel.org,
        robh@...nel.org, krzk+dt@...nel.org, conor+dt@...nel.org,
        gregkh@...uxfoundation.org, jirislaby@...nel.org, broonie@...nel.or,
        andersson@...nel.org, konradybcio@...nel.org, johan+linaro@...nel.org,
        dianders@...omium.org, agross@...nel.org,
        linux-arm-msm@...r.kernel.org, linux-i2c@...r.kernel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-serial@...r.kernel.org, linux-spi@...r.kernel.org,
        quic_msavaliy@...cinc.com, quic_anupkulk@...cinc.com
Subject: Re: [PATCH v2 4/8] dt-bindings: serial: Add support for selecting
 data transfer mode

On 27.01.2025 5:24 PM, Krzysztof Kozlowski wrote:
> On 27/01/2025 15:27, Dmitry Baryshkov wrote:
>> On Mon, Jan 27, 2025 at 08:02:12AM +0100, Krzysztof Kozlowski wrote:
>>> On 24/01/2025 11:53, Viken Dadhaniya wrote:
>>>> Data transfer mode is fixed by TrustZone (TZ), which currently restricts
>>>> developers from modifying the transfer mode from the APPS side.
>>>>
>>>> Document the 'qcom,xfer-mode' properties to select the data transfer mode,
>>>> either GPI DMA (Generic Packet Interface) or non-GPI mode (PIO/CPU DMA).
>>>>
>>>> UART controller can operate in one of two modes based on the
>>>> 'qcom,xfer-mode' property, and the firmware is loaded accordingly.
>>>>
>>>> Co-developed-by: Mukesh Kumar Savaliya <quic_msavaliy@...cinc.com>
>>>> Signed-off-by: Mukesh Kumar Savaliya <quic_msavaliy@...cinc.com>
>>>> Signed-off-by: Viken Dadhaniya <quic_vdadhani@...cinc.com>
>>>> ---
>>>>
>>>> v1 -> v2:
>>>>
>>>> - Drop 'qcom,load-firmware' property and add 'firmware-name' property in
>>>>   qup common driver.
>>>> - Update commit log.
>>>>
>>>> v1 Link: https://lore.kernel.org/linux-kernel/20241204150326.1470749-4-quic_vdadhani@quicinc.com/
>>>> ---
>>>> ---
>>>>  .../devicetree/bindings/serial/qcom,serial-geni-qcom.yaml | 8 ++++++++
>>>>  1 file changed, 8 insertions(+)
>>>>
>>>> diff --git a/Documentation/devicetree/bindings/serial/qcom,serial-geni-qcom.yaml b/Documentation/devicetree/bindings/serial/qcom,serial-geni-qcom.yaml
>>>> index dd33794b3534..383773b32e47 100644
>>>> --- a/Documentation/devicetree/bindings/serial/qcom,serial-geni-qcom.yaml
>>>> +++ b/Documentation/devicetree/bindings/serial/qcom,serial-geni-qcom.yaml
>>>> @@ -56,6 +56,13 @@ properties:
>>>>    reg:
>>>>      maxItems: 1
>>>>  
>>>> +  qcom,xfer-mode:
>>>> +    description: Set the value to 1 for non-GPI (FIFO/CPU DMA) mode and 3 for GPI DMA mode.
>>>> +      The default mode is FIFO.
>>>> +    $ref: /schemas/types.yaml#/definitions/uint32
>>>> +    enum: [1, 3]
>>>> +
>>>> +
>>>
>>> Just one blank line, but anyway, this property should not be in three
>>> places. Do you really expect that each of serial engines within one
>>> GeniQUP will be configured differently by TZ?
>>
>> Yes, each SE is configured separately and it's quite frequent when
>> different SEs have different DMA configuration.
> 
> Well, I checked at sm8550 and sm8650 and each pair of SE - which shares
> resources - has the same DMAs, so I would not call it frequent. Care to
> bring an example where same serial engines have different DMAs and
> different TZ? We do not talk about single QUP.
> 
> Anyway, if you need property per node, this has to be shared schema.

I'd rather ask a different question.. Is there *any* reason to not use
DMA for protocols that support it?

Konrad