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

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Message-ID: <23a9b13c-0bb8-4145-8e1b-4624d13538c4@oss.qualcomm.com>
Date: Tue, 28 Jan 2025 12:40:54 +0100
From: Konrad Dybcio <konrad.dybcio@....qualcomm.com>
To: Konrad Dybcio <konrad.dybcio@....qualcomm.com>,
        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 6:50 PM, Konrad Dybcio wrote:
> 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?

If not, we can simplify this to:

xfer_mode = protocol == PROTOCOL_UART ? XFER_FIFO : XFER_DMA

Konrad