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

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Message-ID: <20240910101137.GD6996@pendragon.ideasonboard.com>
Date: Tue, 10 Sep 2024 13:11:37 +0300
From: Laurent Pinchart <laurent.pinchart@...asonboard.com>
To: Tomi Valkeinen <tomi.valkeinen@...asonboard.com>
Cc: Jacopo Mondi <jacopo.mondi@...asonboard.com>,
	Sakari Ailus <sakari.ailus@...ux.intel.com>,
	Mauro Carvalho Chehab <mchehab@...nel.org>,
	Raspberry Pi Kernel Maintenance <kernel-list@...pberrypi.com>,
	Rob Herring <robh+dt@...nel.org>,
	Krzysztof Kozlowski <krzk@...nel.org>,
	Conor Dooley <conor+dt@...nel.org>,
	Florian Fainelli <florian.fainelli@...adcom.com>,
	Broadcom internal kernel review list <bcm-kernel-feedback-list@...adcom.com>,
	oe-kbuild-all@...ts.linux.dev, linux-media@...r.kernel.org,
	linux-kernel@...r.kernel.org, devicetree@...r.kernel.org,
	linux-rpi-kernel@...ts.infradead.org,
	linux-arm-kernel@...ts.infradead.org,
	Naushir Patuck <naush@...pberrypi.com>,
	Kieran Bingham <kieran.bingham@...asonboard.com>,
	kernel test robot <lkp@...el.com>
Subject: Re: [PATCH v4 3/4] media: raspberrypi: Add support for RP1-CFE

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 ?

> 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.

-- 
Regards,

Laurent Pinchart