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

Konrad Dybcio
2025-01-27T17:50:41Z

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@quicinc.com>
>>>> Signed-off-by: Mukesh Kumar Savaliya <quic_msavaliy@quicinc.com>
>>>> Signed-off-by: Viken Dadhaniya <quic_vdadhani@quicinc.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