linux-kernel - Re: [PATCH V1] i2c: busses: tegra: Add suspend-resume support

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Date:   Fri, 31 May 2019 01:50:29 -0700
From:   Bitan Biswas <bbiswas@...dia.com>
To:     Dmitry Osipenko <digetx@...il.com>,
        Laxman Dewangan <ldewangan@...dia.com>,
        Thierry Reding <treding@...dia.com>,
        Jonathan Hunter <jonathanh@...dia.com>,
        <linux-i2c@...r.kernel.org>, <linux-tegra@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>
CC:     Shardar Mohammed <smohammed@...dia.com>,
        Sowjanya Komatineni <skomatineni@...dia.com>,
        Mantravadi Karthik <mkarthik@...dia.com>
Subject: Re: [PATCH V1] i2c: busses: tegra: Add suspend-resume support



On 5/30/19 4:27 AM, Dmitry Osipenko wrote:
> 30.05.2019 8:55, Bitan Biswas пишет:
>> Post suspend I2C registers have power on reset values. Before any
>> transfer initialize I2C registers to prevent I2C transfer timeout
>> and implement suspend and resume callbacks needed. Fix below errors
>> post suspend:
>>
>> 1) Tegra I2C transfer timeout during jetson tx2 resume:
>>
>> [   27.520613] pca953x 1-0074: calling pca953x_resume+0x0/0x1b0 @ 2939, parent: i2c-1
>> [   27.633623] tegra-i2c 3160000.i2c: i2c transfer timed out
>> [   27.639162] pca953x 1-0074: Unable to sync registers 0x3-0x5. -110
>> [   27.645336] pca953x 1-0074: Failed to sync GPIO dir registers: -110
>> [   27.651596] PM: dpm_run_callback(): pca953x_resume+0x0/0x1b0 returns -110
>> [   27.658375] pca953x 1-0074: pca953x_resume+0x0/0x1b0 returned -110 after 127152 usecs
>> [   27.666194] PM: Device 1-0074 failed to resume: error -110
>>
>> 2) Tegra I2C transfer timeout error on jetson Xavier post resume.
>>
>> Signed-off-by: Bitan Biswas <bbiswas@...dia.com>
>> ---
>>   drivers/i2c/busses/i2c-tegra.c | 24 ++++++++++++++++++++++++
>>   1 file changed, 24 insertions(+)
>>
>> diff --git a/drivers/i2c/busses/i2c-tegra.c b/drivers/i2c/busses/i2c-tegra.c
>> index ebaa78d..f6a377f 100644
>> --- a/drivers/i2c/busses/i2c-tegra.c
>> +++ b/drivers/i2c/busses/i2c-tegra.c
>> @@ -1687,9 +1687,33 @@ static int tegra_i2c_remove(struct platform_device *pdev)
>>   }
>>   
>>   #ifdef CONFIG_PM_SLEEP
>> +static int tegra_i2c_suspend(struct device *dev)
>> +{
>> +	struct tegra_i2c_dev *i2c_dev = dev_get_drvdata(dev);
>> +
>> +	i2c_mark_adapter_suspended(&i2c_dev->adapter);
>> +
>> +	return 0;
>> +}
>> +
>> +static int tegra_i2c_resume(struct device *dev)
>> +{
>> +	struct tegra_i2c_dev *i2c_dev = dev_get_drvdata(dev);
>> +	int ret;
>> +
>> +	i2c_lock_bus(&i2c_dev->adapter, I2C_LOCK_ROOT_ADAPTER);
>> +	ret = tegra_i2c_init(i2c_dev, false);
>> +	i2c_unlock_bus(&i2c_dev->adapter, I2C_LOCK_ROOT_ADAPTER);
> 
> Why the locking is needed here?

async resume could result in stress test issues if some client accesses 
the i2c instance. This ensures the i2c instance is locked till the 
initialization is complete.

> 
>> +	if (!ret)
>> +		i2c_mark_adapter_resumed(&i2c_dev->adapter);
>> +
>> +       return ret;
> 
> A very minor nit.. will be a bit more straightforward to write this as:
> 
> 	int err;
> 
> 	err = tegra_i2c_init(i2c_dev, false);
> 	if (err)
> 		return err;
> 
> 	i2c_mark_adapter_resumed(&i2c_dev->adapter);
> 
> 	return 0;
> 
> It is always cleaner to return 0 on success.
Thanks. I shall update the section in patch as per this suggestion.

-regards,
  Bitan