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

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Message-ID: <cbbb78c9-54ec-453a-92ec-6b174bd3d9cb@quicinc.com>
Date: Mon, 18 Nov 2024 11:15:54 +0530
From: Mukesh Kumar Savaliya <quic_msavaliy@...cinc.com>
To: Konrad Dybcio <konrad.dybcio@....qualcomm.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

Thanks for the review konrad !

On 11/16/2024 12:58 AM, Konrad Dybcio wrote:
> 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?
Actually, HW register doesn't provide such mechanism, it's add on 
feature if SE is programmed for GSI mode.
> 
>> 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
> 
To clarify - Does it mean i should not have SW disable this feature OR 
override  ? And let it continue in non GSI mode even it's not going to 
work ?
>>
>> 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..
we can have Some SW logging added ?
> 
> Konrad