linux-kernel - Re: [PATCH v4 4/4] i2c: i2c-qcom-geni: Enable i2c controller sharing between two subsystems

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Message-ID: <37762281-4903-4b2d-8f44-3cc4d988558d@oss.qualcomm.com>
Date: Fri, 15 Nov 2024 20:28:47 +0100
From: Konrad Dybcio <konrad.dybcio@....qualcomm.com>
To: Mukesh Kumar Savaliya <quic_msavaliy@...cinc.com>,
        konrad.dybcio@...aro.org, andersson@...nel.org, andi.shyti@...nel.org,
        linux-arm-msm@...r.kernel.org, dmaengine@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-i2c@...r.kernel.org,
        conor+dt@...nel.org, agross@...nel.org, devicetree@...r.kernel.org,
        vkoul@...nel.org, linux@...blig.org, dan.carpenter@...aro.org,
        Frank.Li@....com, konradybcio@...nel.org, bryan.odonoghue@...aro.org,
        krzk+dt@...nel.org, robh@...nel.org
Cc: quic_vdadhani@...cinc.com
Subject: Re: [PATCH v4 4/4] i2c: i2c-qcom-geni: Enable i2c controller sharing
 between two subsystems

On 13.11.2024 5:14 PM, Mukesh Kumar Savaliya wrote:
> Add support to share I2C controller in multiprocessor system in a mutually
> exclusive way. Use "qcom,shared-se" flag in a particular i2c instance node
> if the usecase requires i2c controller to be shared.

Can we read back some value from the registers to know whether such sharing
takes place?

> Sharing of I2C SE(Serial engine) is possible only for GSI mode as client
> from each processor can queue transfers over its own GPII Channel. For
> non GSI mode, we should force disable this feature even if set by user
> from DT by mistake.

The DT is to be taken authoritatively

> 
> I2C driver just need to mark first_msg and last_msg flag to help indicate
> GPI driver to take lock and unlock TRE there by protecting from concurrent
> access from other EE or Subsystem.
> 
> gpi_create_i2c_tre() function at gpi.c will take care of adding Lock and
> Unlock TRE for the respective transfer operations.
> 
> Since the GPIOs are also shared between two SS, do not unconfigure them
> during runtime suspend. This will allow other SS to continue to transfer
> the data without any disturbance over the IO lines.
> 
> For example, Assume an I2C EEPROM device connected with an I2C controller.
> Each client from ADSP and APPS processor can perform i2c transactions
> without any disturbance from each other.
> 
> Signed-off-by: Mukesh Kumar Savaliya <quic_msavaliy@...cinc.com>
> ---

[...]

>  	} else {
>  		gi2c->gpi_mode = false;
> +
> +		/* Force disable shared SE case for non GSI mode */
> +		gi2c->se.shared_geni_se = false;

Doing this silently sounds rather odd..

Konrad