Re: [PATCH v4 3/4] media: raspberrypi: Add support for RP1-CFE

[Sakari Ailus <sakari.ailus@linux.intel.com>]

Hi Laurent,

On Tue, Sep 10, 2024 at 01:11:37PM +0300, Laurent Pinchart wrote:
> On Tue, Sep 10, 2024 at 12:56:38PM +0300, Tomi Valkeinen wrote:
> > On 10/09/2024 12:19, Jacopo Mondi wrote:
> > 
> > > However, I think this current patch is correct (assuming the above
> > > reasoning on i2c sensor drivers is correct) and doesn't require
> > > CONFIG_PM, so I would be tempted to keep this version.
> > 
> > I think the existence of this discussion alone proves my point that we 
> > should only support PM-case, unless !PM is a requirement =).
> 
> For me it proves there's a dire need to document the runtime PM API in a
> way that a human could understand :-)
> 
> > But if you do want to keep !PM:
> > 
> > Is there a reason why not mark the device as active with 
> > pm_runtime_set_active() after calling pispbe_runtime_resume and before 
> > accessing the device? That feels like the most logical way to use the 
> > function, and it would be right regardless whether the core will enable 
> > the parents before probe() or not.
> 
> Does pm_runtime_set_active() resume the parent ?

No, it simply sets the device's runtime PM status.

> 
> > And not related to the BE or CFE drivers, but it strikes me odd that to 
> > support PM and !PM we need to play with these tricks. I think the core 
> > should just do the right thing if the driver does pm_runtime_get_sync() 
> > even with !PM (although maybe the time has passed to be able to do that).
> 
> The runtime PM concepts are nice, but the API is wrong in my opinion.
> Instead of being designed to expose the internals of runtime PM, it
> should focus on usability from a driver point of view first.

It's been moving a little bit to that direction, largely with new helper
functions.

I²C devices have been powered on for probe since commit a76e9bd89ae70 .
Relation to runtime PM wasn't considered at the time, apparently.

-- 
Kind regards,

Sakari Ailus