Re: [PATCH v1] i2c: tegra: Remove suspend-resume

[Laxman Dewangan]

On Monday 14 May 2018 05:29 PM, Thierry Reding wrote:
> * PGP Signed by an unknown key
>
> On Mon, May 14, 2018 at 12:13:47AM +0300, Dmitry Osipenko wrote:
> > Nothing prevents I2C clients to access I2C while Tegra's driver is being
> > suspended, this results in -EBUSY error returned to the clients and that
> > may have unfortunate consequences. In particular this causes problems
> > for the TPS6586x MFD driver which emits hundreds of "failed to read
> > interrupt status" error messages on resume from suspend. This happens if
> > TPS6586X is used to wake system from suspend by the expired RTC alarm
> > timer because TPS6586X is an I2C device driver and its IRQ handler reads
> > the status register while Tegra's I2C driver is suspended, i.e. just after
> > kernel enabled IRQ's during of resume-from-suspend process.
> >
> > Note that the removed tegra_i2c_resume() invoked tegra_i2c_init() which
> > performs HW reset. That seems was also not entirely correct because moving
> > tegra_i2c_resume to an earlier stage of resume-from-suspend process causes
> > I2C transfer to fail in the case of TPS6586X. It is fine to remove the
> > HW-reinitialization for now because it should be only needed in a case of
> > using lowest power-mode during suspend, which upstream kernel doesn't
> > support.
> >
> > Signed-off-by: Dmitry Osipenko <digetx@xxxxxxxxx>
> > Cc: <stable@xxxxxxxxxxxxxxx>
> > ---
> >   drivers/i2c/busses/i2c-tegra.c | 33 ---------------------------------
> >   1 file changed, 33 deletions(-)
> Shardar, Laxman, any thoughts on this? The is_suspended thing looks to
> me like a workaround of some sort that may not be needed if clients have
> proper suspend/resume implementations. Even without suspend/resume
> support in client drivers, the driver core should resume devices in the
> right order (I2C adapter before any of the clients), so I don't see any
> cases where the is_suspended logic would be useful.

Our I2C driver is based on the interrupt. So we have converted the 
suspend/resume to suspend_noirq and reseume_noirq so that we will not 
allow the transfer when system interrupt disabled in downstream.
          SET_NOIRQ_SYSTEM_SLEEP_PM_OPS(tegra_i2c_suspend, 
tegra_i2c_resume)

In shutdown path, where interrupt disabled and still need i2c, we use 
the bit-bang method via GPIO for i2c transfer.