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

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Message-ID: <6736db20-127b-45c3-ac90-3e3e359c343b@quicinc.com>
Date: Tue, 10 Dec 2024 10:58:03 +0530
From: Viken Dadhaniya <quic_vdadhani@...cinc.com>
To: Doug Anderson <dianders@...omium.org>
CC: <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>,
        <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_anupkulk@...cinc.com>,
        Mukesh Kumar Savaliya
	<quic_msavaliy@...cinc.com>
Subject: Re: [PATCH v1 1/7] dt-bindings: i2c: qcom,i2c-geni: Document DT
 properties for QUP firmware loading



On 12/4/2024 10:55 PM, Doug Anderson wrote:
> Hi,
> 
> On Wed, Dec 4, 2024 at 7:03 AM Viken Dadhaniya
> <quic_vdadhani@...cinc.com> 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@...cinc.com>
>> Signed-off-by: Mukesh Kumar Savaliya <quic_msavaliy@...cinc.com>
>> Signed-off-by: Viken Dadhaniya <quic_vdadhani@...cinc.com>
>> ---
>>   .../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?

Yes, correct, Will update in V2.
I plan to add 2 modes, GSI and non-GSI(PIO or DMA based on length).

> 
> 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

GSI firmware is loaded from TZ per QUP, but to use GSI mode,
we need to configure the SE to use GSI mode by writing into SE register 
QUPV3_SE_GENI_DMA_MODE_EN and SE_GSI_EVENT_EN. This register is
used to configure data transfer mode for Serial Engine.