Re: omap-i2c: runtime pm issue during suspend to ram

["Théo Lebrun" <theo.lebrun@bootlin.com>]

Hello,

On Wed Dec 20, 2023 at 12:36 PM CET, Thomas Richard wrote:
> On 12/20/23 12:14, Tony Lindgren wrote:
> > * Thomas Richard <thomas.richard@bootlin.com> [231220 10:50]:
> >> On 12/19/23 18:15, Thomas Richard wrote:
> >>> Hello,
> >>
> >> I add some people in this thread.
> >>
> >>>
> >>> I have a gpio expander (pca953x driver) connected to an i2c controller
> >>> managed by the omap-i2c driver.
> >>> And I have some issues with pm_runtime_force_suspend/resume during
> >>> suspend to ram.
> >>> For some reasons, related to hardware design, I need to access to this
> >>> gpio expander during suspend_noirq and resume_noirq. So I had to move
> >>> the suspend/resume of the pca953x to suspend_noirq/resume_noirq.
> > 
> > Hmm at noirq level you need to do polling on the i2c controller?
>
> Hello Tony,
>
> Thanks for your reply.
>
> No, irq is still active in suspend_noirq for this i2c controller due to
> the flag IRQF_NO_SUSPEND [1].
> If this flag is set, the interrupt is still enabled in suspend_noirq [2].
>
> [1]
> https://elixir.bootlin.com/linux/v6.7-rc6/source/drivers/i2c/busses/i2c-omap.c#L1473
> [2]
> https://www.kernel.org/doc/html/latest/power/suspend-and-interrupts.html#the-irqf-no-suspend-flag
>
> > 
> >>> diff --git a/drivers/i2c/busses/i2c-omap.c b/drivers/i2c/busses/i2c-omap.c
> >>> index 42165ef57946..fe79b27b46fd 100644
> >>> --- a/drivers/i2c/busses/i2c-omap.c
> >>> +++ b/drivers/i2c/busses/i2c-omap.c
> >>> @@ -1575,9 +1575,24 @@ static int __maybe_unused
> >>> omap_i2c_runtime_resume(struct device *dev)
> >>>         return 0;
> >>>  }
> >>>
> >>> +static int omap_i2c_suspend(struct device *dev)
> >>> +{
> >>> +       pm_runtime_get_sync(dev);
> >>> +       pm_runtime_disable(dev);
> >>> +       return 0;
> >>> +}
> > 
> > If you want the i2c controller enabled during suspend, you can leave it
> > enabled above, and as we already have SET_NOIRQ_SYSTEM_SLEEP_PM_OPS
> > doing force_suspend() and force_resume(), you can runtime PM put on
> > resume. So something like below might do the trick:
>
> Ok I'll test it. Thanks

The issue with this approach is that it requires knowing at suspend-time
if the controller will be used at resume_noirq-time. Ideally the
controller's behavior would not be modified until a xfer is done at
resume_noirq time. There are many platforms that use this driver that
probably don't need the controller woken up.

Thanks,

--
Théo Lebrun, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com