Re: [RFC/RFT 00/10] i2c: move handling of suspended adapters to the core

[Hans de Goede]

Hi,

On 18-12-18 21:17, Wolfram Sang wrote:
> Hans, all,
>
> > > ... this. I don't know what these flags do (and reading SMART in there
> > > gives me more a 'uh-oh' feeling)
> >
> > On x86 the lines between runtime suspend and system-suspend are blurring
> > with technologies like "connected standby" and in general devices moving
> > to suspend2idle as system-suspend state, I guess this also applies to
> > modern smartphone platforms but I'm not following those closely.
>
> I'd guess so, too. I am not aware of any existing mechanism for that at
> the moment, though. If somebody does, please enlighten us.
>
> > The "SMART" bit is really not all that smart, SMART_PREPARE means that
> > the drivers pm prepare callback will return positive non 0 (e.g. 1) to
> > indicate that the device may not be kept in its runtime suspended
> > state when transitioning to system-suspend, otoh when the prepare
> > callback returns 0 and the SMART_PREPARE flag is set then *all* suspend/
> > resume handling can be skipped during a system suspend.
>
> Thanks for the detailed explanation! Much appreciated.
>
> > > Looking at the open coded version you did for the designware driver, I
> > > wonder now if it is better to just leave it at driver level? Need to
> > > sleep over it, though.
> >
> > I myself was thinking in the same direction (leave the entire suspended
> > check at the driver level).
>
> So, I was giving it some more thoughts, and my feeling is to still apply
> this series with the review comments addressed. Plus, clearly mark the
> new 'is_suspended' flag and the helper function as *optional* to allow
> for driver specific solutions as well. The then-to-be-added
> documentation would state that it is mostly useful for seperated system
> suspend and runtime suspend. For more complex situations, custom
> solutions are accepted, too. Which means your patch for designware
> should be added to the series.
>
> My take is there are enough drivers out there already which can benefit
> from this new helper. If it turns out to be useless somewhen in the
> future, we can still remove it.
>
> What do you (and all others, of course) think?

I've been thinking along the same lines: your series for the drivers
with separate runtime and system suspend handlers, "custom" driver
specific code for troublesome cases like i2c-designware.

Do you want me to send out a new version of my patch for the i2c-designware
code?

Regards,

Hans