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

[Laurent Pinchart]

On Mon, Sep 09, 2024 at 03:29:30PM +0200, Jacopo Mondi wrote:
> On Mon, Sep 09, 2024 at 01:04:35PM GMT, Tomi Valkeinen wrote:
> > On 09/09/2024 12:13, Jacopo Mondi wrote:
> > > On Mon, Sep 09, 2024 at 08:22:59AM GMT, Tomi Valkeinen wrote:
> > > > On 09/09/2024 08:08, Tomi Valkeinen wrote:
> > > > > On 05/09/2024 14:11, Laurent Pinchart wrote:
> > > > > > On Thu, Sep 05, 2024 at 06:50:48PM +0800, kernel test robot wrote:
> > > > > > > Hi Tomi,
> > > > > > >
> > > > > > > kernel test robot noticed the following build warnings:
> > > > > > >
> > > > > > > [auto build test WARNING on 431c1646e1f86b949fa3685efc50b660a364c2b6]
> > > > > > >
> > > > > > > url:    https://github.com/intel-lab-lkp/linux/commits/Tomi-
> > > > > > > Valkeinen/media-uapi-Add-meta-formats-for-PiSP-FE-config-and-
> > > > > > > stats/20240904-192729
> > > > > > > base:   431c1646e1f86b949fa3685efc50b660a364c2b6
> > > > > > > patch link:    https://lore.kernel.org/r/20240904-rp1-cfe-v4-3-
> > > > > > > f1b5b3d69c81%40ideasonboard.com
> > > > > > > patch subject: [PATCH v4 3/4] media: raspberrypi: Add support
> > > > > > > for RP1-CFE
> > > > > > > config: m68k-allmodconfig (https://download.01.org/0day-ci/
> > > > > > > archive/20240905/202409051822.ZzUGw3XQ-lkp@xxxxxxxxx/config)
> > > > > > > compiler: m68k-linux-gcc (GCC) 14.1.0
> > > > > > > reproduce (this is a W=1 build):
> > > > > > > (https://download.01.org/0day-ci/
> > > > > > > archive/20240905/202409051822.ZzUGw3XQ-lkp@xxxxxxxxx/reproduce)
> > > > > > >
> > > > > > > If you fix the issue in a separate patch/commit (i.e. not just a
> > > > > > > new version of
> > > > > > > the same patch/commit), kindly add following tags
> > > > > > > | Reported-by: kernel test robot <lkp@xxxxxxxxx>
> > > > > > > | Closes: https://lore.kernel.org/oe-kbuild-
> > > > > > > all/202409051822.ZzUGw3XQ-lkp@xxxxxxxxx/
> > > > > > >
> > > > > > > All warnings (new ones prefixed by >>):
> > > > > > >
> > > > > > > > > drivers/media/platform/raspberrypi/rp1-cfe/cfe.c:2445:12:
> > > > > > > > > warning: 'cfe_runtime_resume' defined but not used
> > > > > > > > > [-Wunused-function]
> > > > > > >       2445 | static int cfe_runtime_resume(struct device *dev)
> > > > > > >            |            ^~~~~~~~~~~~~~~~~~
> > > > > > > > > drivers/media/platform/raspberrypi/rp1-cfe/cfe.c:2435:12:
> > > > > > > > > warning: 'cfe_runtime_suspend' defined but not used
> > > > > > > > > [-Wunused-function]
> > > > > > >       2435 | static int cfe_runtime_suspend(struct device *dev)
> > > > > > >            |            ^~~~~~~~~~~~~~~~~~~
> > > > > > > vim +/cfe_runtime_resume +2445
> > > > > > > drivers/media/platform/raspberrypi/ rp1-cfe/cfe.c
> > > > > >
> > > > > > The recommended way to fix this is to switch from SET_RUNTIME_PM_OPS()
> > > > > > to RUNTIME_PM_OPS() and use pm_ptr() to set .driver.pm. This being said,
> > > > > > the driver won't work on a kernel with !CONFIG_PM given how you
> > > > > > implemented probe() and remove().
> > > > > >
> > > > > > The pisp-be driver suffered from the same issue and Jacopo fixed it in
> > > > > > the last version. You can have a look at implement something similar.
> > > > >
> > > > > I can't right away think of any reason to not just depend on CONFIG_PM
> > > > > and be done with it without any tricks. Do you know if there's a reason?
> > >
> > > We had the same discussion, and even if I would be fine depending on
> > > CONFIG_PM, supporting !CONFIG_PM is not that much work, I kept it as
> > > an optional dependency (it was suggested during the review as well)
> > >
> > > >
> > > > Also, I don't think pisp-be is correct. It just calls
> > > > pispbe_runtime_resume() in probe() to wake the IP up (which only enables
> > > > pisp clock), without telling the runtime PM about it. This means the parent
> > > > device and the suppliers may not be powered up.
> > >
> > > Are you referring to the code currently in the tree or to this patch ?
> > > https://patchwork.linuxtv.org/project/linux-media/patch/20240904095836.344833-5-jacopo.mondi@xxxxxxxxxxxxxxxx/
> >
> > Ah, I missed that one.
> >
> > I don't think it fixes the issue I mentioned. If we have PM enabled, and the
> > parent device requires powering up for the child device (BE) to be
> > accessible, the driver will crash when calling pispbe_hw_init(). I think you
> > should call pm_runtime_set_active() before calling pispbe_runtime_resume().
> 
> As discussed, this is not a problem currently for BE, but indeed you
> have a point.
> 
> Sad note: most of all the occurrences of "grep set_active" in
> drivers/media/platform/ show that set_active() is used as I've done in
> my patch
> 
> > However, you said above that "supporting !CONFIG_PM is not that much work".
> > Maybe not. But how much work is it to get it right (for both PM and !PM),
> > and make sure it stays right? =).
> >
> > Just my opinion, but if there are zero use cases for the !PM, I would just
> > go with "depends on PM" to keep the driver simpler, less bug-prone, and
> > easier to maintain.

I'm fine with that, and for platform drivers, that's my preferred
option. Sakari ?

> I don't see a use case for !PM and we confirmed with RPi they don't
> need to support it. During the review of a previous version of the BE
> driver iirc I've been asked to support !PM but I'm not sure I recall
> the reasons.

I hope it wasn't me :-)

-- 
Regards,

Laurent Pinchart