Re: [PATCH v1 1/7] dt-bindings: i2c: qcom,i2c-geni: Document DT properties for QUP firmware loading

[Doug Anderson <dianders@xxxxxxxxxxxx>]

Hi,

On Wed, Dec 4, 2024 at 7:03 AM Viken Dadhaniya
<quic_vdadhani@xxxxxxxxxxx> wrote:
>
> Document the 'qcom,load-firmware' and 'qcom,xfer-mode' properties to
> support SE(Serial Engine) firmware loading from the protocol driver and to
> select the data transfer mode, either GPI DMA (Generic Packet Interface)
> or non-GPI mode (PIO/CPU DMA).
>
> I2C 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@xxxxxxxxxxx>
> Signed-off-by: Mukesh Kumar Savaliya <quic_msavaliy@xxxxxxxxxxx>
> Signed-off-by: Viken Dadhaniya <quic_vdadhani@xxxxxxxxxxx>
> ---
>  .../devicetree/bindings/i2c/qcom,i2c-geni-qcom.yaml   | 11 +++++++++++
>  1 file changed, 11 insertions(+)
>
> diff --git a/Documentation/devicetree/bindings/i2c/qcom,i2c-geni-qcom.yaml b/Documentation/devicetree/bindings/i2c/qcom,i2c-geni-qcom.yaml
> index 9f66a3bb1f80..a26f34fce1bb 100644
> --- a/Documentation/devicetree/bindings/i2c/qcom,i2c-geni-qcom.yaml
> +++ b/Documentation/devicetree/bindings/i2c/qcom,i2c-geni-qcom.yaml
> @@ -66,6 +66,15 @@ properties:
>    required-opps:
>      maxItems: 1
>
> +  qcom,load-firmware:
> +    type: boolean
> +    description: Optional property to load SE (serial engine) Firmware from protocol driver.
> +
> +  qcom,xfer-mode:
> +    description: Value 1,2 and 3 represents FIFO, CPU DMA and GSI DMA mode respectively.
> +    $ref: /schemas/types.yaml#/definitions/uint32
> +    enum: [1, 2, 3]

I'm a little confused about this. I'll admit I haven't fully analyzed
your patch with actual code in it, but in the past "CPU DMA" mode and
"FIFO" mode were compatible with each other and then it was up to the
driver to decide which of the two modes made sense in any given
situation. For instance, last I looked at the i2c driver it tried to
use DMA for large transfers and FIFO for small transfers. The SPI
driver also has some cases where it will use DMA mode and then
fallback to FIFO mode.

...so what exactly is the point of differentiating between "FIFO" and
"CPU DMA" mode here?

Then when it comes to "GSI DMA" mode, my understanding is that the
firmware for "GSI DMA" mode is always loaded by Trustzone because the
whole point is that the GSI mode arbitrates between multiple clients.
Presumably if the firmware already loaded the GSI firmware then the
code would just detect that case. ...so there shouldn't need to be any
reason to specify GSI mode here either, right?

-Doug