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Date:   Thu, 6 Jun 2019 06:55:44 -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 6/6/19 4:52 AM, Dmitry Osipenko wrote:
> 06.06.2019 8:43, Bitan Biswas пишет:
>>
>>
>> On 5/31/19 5:43 AM, Dmitry Osipenko wrote:
>>> 31.05.2019 11:50, Bitan Biswas пишет:
>>>>
>>>>
>>>> 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.
>>>
>>> 1) This doesn't make much sense.. if client could access I2C during of
>>> tegra_i2c_init execution, then what stops it to perform the access
>>> before the lock is taken?
>> Client resumes will start after I2C instance resume because of driver
>> dependency. Since lock is the first call in i2c-tegra I believe I2C
>> calls of client will not start.
> 
> You're incorrectly assuming that client can start resuming in the middle
> of the controller's resume process. I2C client's resume won't start
> until tegra_i2c_resume() is finished completely. That is because child
> drivers are resumed only after theirs parent is ready and this is
> guaranteed by the drivers core.
> 
Agreed.

-regards,
  Bitan

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