linux-kernel - Re: [PATCH v2 2/8] dt-bindings: i2c: qcom,i2c-geni: Add support for selecting data transfer mode

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Message-ID: <ewwk5tvwlhu7cbev7su75ysooboq7ivloydvd3unwic2e6p7ap@bpyoqsrgvf6f>
Date: Fri, 24 Jan 2025 17:03:36 +0200
From: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To: Viken Dadhaniya <quic_vdadhani@...cinc.com>
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, 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 2/8] dt-bindings: i2c: qcom,i2c-geni: Add support for
 selecting data transfer mode

On Fri, Jan 24, 2025 at 05:52:24PM +0530, Viken Dadhaniya wrote:
> 
> 
> On 1/24/2025 4:48 PM, Dmitry Baryshkov wrote:
> > On Fri, Jan 24, 2025 at 04:23:03PM +0530, 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).
> > > 
> > > I2C controller can operate in one of two modes based on the
> > > 'qcom,xfer-mode' property, and the firmware is loaded accordingly.
> > 
> > Is it possible to load the firmware after it being loaded by TZ? Is it
> > possible to change the mode at runtime too?
> 
> No, firmware can be loaded either from the TZ side or APPS side.

You answer actually reads as "No, yes" (excuse me, non-native here).
Most likely you mean that it can not be reloaded once either TZ or APPS
has loaded it.

> In non-GPI mode, the transfer mode will change runtime between PIO and CPU
> DMA based on the data length.
> 
> We need to update the device tree property(qcom,xfer-mode) to change the
> mode between non-GPI and GPI.

So, is it actually possible to change the mode? E.g. if the TZ has
loaded the firmware and configured SE for PIO/SE DMA, is it possible to
change it to GPI DMA?

> 
> > 
> > > 
> > > 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/20241204150326.1470749-2-quic_vdadhani@quicinc.com/
> > > ---
> > > ---
> > >   .../devicetree/bindings/i2c/qcom,i2c-geni-qcom.yaml        | 7 +++++++
> > >   1 file changed, 7 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..68e4bf0c84d1 100644
> > > --- a/Documentation/devicetree/bindings/i2c/qcom,i2c-geni-qcom.yaml
> > > +++ b/Documentation/devicetree/bindings/i2c/qcom,i2c-geni-qcom.yaml
> > > @@ -66,6 +66,12 @@ properties:
> > >     required-opps:
> > >       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]
> > > +
> > >   required:
> > >     - compatible
> > >     - interrupts
> > > @@ -142,5 +148,6 @@ examples:
> > >           interconnect-names = "qup-core", "qup-config", "qup-memory";
> > >           power-domains = <&rpmhpd SC7180_CX>;
> > >           required-opps = <&rpmhpd_opp_low_svs>;
> > > +        qcom,xfer-mode = <1>;
> > 
> > What does <1> mean? Please provide corresponding defines.
> 
> Do we need to add a string instead of a number, like
> include/dt-bindings/dma/qcom-gpi.h?

You need to '#define FOO_BAR 1', then another one for 3. String is a
"string", it's not required here (in my opinion).

-- 
With best wishes
Dmitry