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

[Bitan Biswas]

On 6/6/19 4:52 AM, Dmitry Osipenko wrote:
> 06.06.2019 8:43, Bitan Biswas ÐÐÑÐÑ:
> > On 5/31/19 5:43 AM, Dmitry Osipenko wrote:
> > > 31.05.2019 11:50, Bitan Biswas ÐÐÑÐÑ:
> > > > On 5/30/19 4:27 AM, Dmitry Osipenko wrote:
> > > > > 30.05.2019 8:55, Bitan Biswas ÐÐÑÐÑ:
> > > > > > 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:
> > > > > >
> > > > > > [ÂÂ 27.520613] pca953x 1-0074: calling pca953x_resume+0x0/0x1b0 @
> > > > > > 2939, parent: i2c-1
> > > > > > [ÂÂ 27.633623] tegra-i2c 3160000.i2c: i2c transfer timed out
> > > > > > [ÂÂ 27.639162] pca953x 1-0074: Unable to sync registers 0x3-0x5. -110
> > > > > > [ÂÂ 27.645336] pca953x 1-0074: Failed to sync GPIO dir registers: -110
> > > > > > [ÂÂ 27.651596] PM: dpm_run_callback(): pca953x_resume+0x0/0x1b0
> > > > > > returns -110
> > > > > > [ÂÂ 27.658375] pca953x 1-0074: pca953x_resume+0x0/0x1b0 returned -110
> > > > > > after 127152 usecs
> > > > > > [ÂÂ 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@xxxxxxxxxx>
> > > > > > ---
> > > > > >  ÂÂ drivers/i2c/busses/i2c-tegra.c | 24 ++++++++++++++++++++++++
> > > > > >  ÂÂ 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)
> > > > > >  ÂÂ }
> > > > > >  ÂÂ Â #ifdef CONFIG_PM_SLEEP
> > > > > > +static int tegra_i2c_suspend(struct device *dev)
> > > > > > +{
> > > > > > +ÂÂÂ struct tegra_i2c_dev *i2c_dev = dev_get_drvdata(dev);
> > > > > > +
> > > > > > +ÂÂÂ i2c_mark_adapter_suspended(&i2c_dev->adapter);
> > > > > > +
> > > > > > +ÂÂÂ return 0;
> > > > > > +}
> > > > > > +
> > > > > > +static int tegra_i2c_resume(struct device *dev)
> > > > > > +{
> > > > > > +ÂÂÂ struct tegra_i2c_dev *i2c_dev = dev_get_drvdata(dev);
> > > > > > +ÂÂÂ int ret;
> > > > > > +
> > > > > > +ÂÂÂ i2c_lock_bus(&i2c_dev->adapter, I2C_LOCK_ROOT_ADAPTER);
> > > > > > +ÂÂÂ ret = tegra_i2c_init(i2c_dev, false);
> > > > > > +ÂÂÂ 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