Re: [PATCH] media: i2c: fix max9271 build dependencies

[Mauro Carvalho Chehab <mchehab+huawei@kernel.org>]

Em Mon, 8 Feb 2021 11:24:25 +0200
Sakari Ailus <sakari.ailus@linux.intel.com> escreveu:

> On Mon, Feb 08, 2021 at 10:08:22AM +0100, Mauro Carvalho Chehab wrote:
> > Em Mon, 8 Feb 2021 10:41:47 +0200
> > Sakari Ailus <sakari.ailus@linux.intel.com> escreveu:
> >   
> > > Hi Jacopo,
> > > 
> > > On Mon, Feb 08, 2021 at 09:36:16AM +0100, Jacopo Mondi wrote:  
> > > > Hello everyone,
> > > > 
> > > > On Mon, Feb 08, 2021 at 09:27:01AM +0200, Sakari Ailus wrote:    
> > > > > Hi Mauro,
> > > > >
> > > > > Thanks for the patch.    
> > > > 
> > > > Sorry, that's cleary an oversight from my side.
> > > > Thanks for tackling it.
> > > >     
> > > > >
> > > > > On Mon, Feb 08, 2021 at 07:53:15AM +0100, Mauro Carvalho Chehab wrote:    
> > > > > > As described on its c file, the Maxim MAX9271 GMSL serializer isn't a
> > > > > > self-contained driver, as MAX9271 is usually embedded in camera modules
> > > > > > with at least one image sensor and optional additional components,
> > > > > > such as uController units or ISPs/DSPs.
> > > > > >
> > > > > > After chanseset a59f853b3b4b ("media: i2c: Add driver for RDACM21 camera module"),
> > > > > > there are now two drivers currently needing it: rdacm20 and rdacm21.
> > > > > >
> > > > > > Building with allmodconfig is now causing those warnings:
> > > > > >
> > > > > > 	WARNING: modpost: drivers/media/i2c/rdacm21-camera_module: 'max9271_set_serial_link' exported twice. Previous export was in drivers/media/i2c/rdacm20-camera_module.ko
> > > > > > 	WARNING: modpost: drivers/media/i2c/rdacm21-camera_module: 'max9271_configure_i2c' exported twice. Previous export was in drivers/media/i2c/rdacm20-camera_module.ko
> > > > > > 	WARNING: modpost: drivers/media/i2c/rdacm21-camera_module: 'max9271_set_high_threshold' exported twice. Previous export was in drivers/media/i2c/rdacm20-camera_module.ko
> > > > > > 	WARNING: modpost: drivers/media/i2c/rdacm21-camera_module: 'max9271_configure_gmsl_link' exported twice. Previous export was in drivers/media/i2c/rdacm20-camera_module.ko
> > > > > > 	WARNING: modpost: drivers/media/i2c/rdacm21-camera_module: 'max9271_set_gpios' exported twice. Previous export was in drivers/media/i2c/rdacm20-camera_module.ko
> > > > > > 	WARNING: modpost: drivers/media/i2c/rdacm21-camera_module: 'max9271_clear_gpios' exported twice. Previous export was in drivers/media/i2c/rdacm20-camera_module.ko
> > > > > > 	WARNING: modpost: drivers/media/i2c/rdacm21-camera_module: 'max9271_enable_gpios' exported twice. Previous export was in drivers/media/i2c/rdacm20-camera_module.ko
> > > > > > 	WARNING: modpost: drivers/media/i2c/rdacm21-camera_module: 'max9271_disable_gpios' exported twice. Previous export was in drivers/media/i2c/rdacm20-camera_module.ko
> > > > > > 	WARNING: modpost: drivers/media/i2c/rdacm21-camera_module: 'max9271_verify_id' exported twice. Previous export was in drivers/media/i2c/rdacm20-camera_module.ko
> > > > > > 	WARNING: modpost: drivers/media/i2c/rdacm21-camera_module: 'max9271_set_address' exported twice. Previous export was in drivers/media/i2c/rdacm20-camera_module.ko
> > > > > > 	WARNING: modpost: drivers/media/i2c/rdacm21-camera_module: 'max9271_set_deserializer_address' exported twice. Previous export was in drivers/media/i2c/rdacm20-camera_module.ko
> > > > > > 	WARNING: modpost: drivers/media/i2c/rdacm21-camera_module: 'max9271_set_translation' exported twice. Previous export was in drivers/media/i2c/rdacm20-camera_module.ko
> > > > > >
> > > > > > Address the issue by adding a Kconfig item for it, that it is
> > > > > > seleced if either one of the modules that need max9271 is used.
> > > > > >
> > > > > > Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
> > > > > > Fixes: a59f853b3b4b ("media: i2c: Add driver for RDACM21 camera module")
> > > > > > Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
> > > > > > ---
> > > > > >  drivers/media/i2c/Kconfig  | 10 ++++++++++
> > > > > >  drivers/media/i2c/Makefile |  8 ++++----
> > > > > >  2 files changed, 14 insertions(+), 4 deletions(-)
> > > > > >
> > > > > > diff --git a/drivers/media/i2c/Kconfig b/drivers/media/i2c/Kconfig
> > > > > > index 2d3dc0d82f9e..a6802195d583 100644
> > > > > > --- a/drivers/media/i2c/Kconfig
> > > > > > +++ b/drivers/media/i2c/Kconfig
> > > > > > @@ -712,6 +712,16 @@ config VIDEO_ST_MIPID02
> > > > > >  	  module will be called st-mipid02.
> > > > > >  endmenu
> > > > > >
> > > > > > +#
> > > > > > +# Camera ancillary chips
> > > > > > +#
> > > > > > +
> > > > > > +# MAX9271 is usually embedded in camera modules
> > > > > > +config VIDEO_MAX9271_SERIALIZER
> > > > > > +	tristate
> > > > > > +	default y
> > > > > > +	depends on VIDEO_RDACM20 || VIDEO_RDACM21
> > > > > > +    
> > > > >
> > > > > I'd instead make the RDACM drivers depend on this one instead. The RDACM20
> > > > > driver directly depends on the symbols in the MAX9271 driver.  
> > 
> > While such solution is technically OK, it will make harder for the ones
> > wanting to use the RDACM drivers, because those two drivers will be
> > ridden at the config menu, until MAX9271 got selected.
> > 
> > With the above solution, this driver will be auto-selected if either
> > RDACM20 or RDACM21 is needed.
> > 
> > Btw, this is exactly the same strategy we use for tuner I2C modules:
> > the user doesn't need to know that his board uses tuner "foo" or "bar".
> > All it needs is to know that it will require, for instance, the em28xx
> > driver.
> >   
> > > > >    
> > > > 
> > > > OTOH I it makes sense to have MAX9271 depend on the camera modules, as
> > > > selecting the serializer alone is not that useful.
> > > > 
> > > > Could the two camera modules symbols instead select the MAX9271 one ?    
> > > 
> > > MAX9271 could be used elsewhere than in RDACM* devices.  
> > 
> > Sure, but then it is just a matter of adding the other driver there:
> > 
> > 	depends on VIDEO_RDACM20 || VIDEO_RDACM21 || VIDEO_FOO
> > 
> > To be frank, I doubt that we'll end having dozens of boards with this.
> > If we end having lots of drivers, we can work on a different
> > solution.  
> 
> Also note that there will be combinations of something compiled as a module
> and another driver linked directly to the kernel.
> 
> So each of the RDACM drivers would likely also need:
> 
> 	depends on VIDEO_MAX9271_SERIALIZER || !VIDEO_MAX9271_SERIALIZER

No. I fail to see where this would work, as MAX9271 is a mandatory
dependency of those drivers. See:

	static int rdacm20_s_stream(struct v4l2_subdev *sd, int enable)
	{
	        struct rdacm20_device *dev = sd_to_rdacm20(sd);
	
	        return max9271_set_serial_link(dev->serializer, enable);
	}


Without compiling max9271, the device won't stream ;-)

-

Yet, assuming that this could be an optional feature, if you use this:

	config VIDEO_MAX9271_SERIALIZER
		tristate
		default y
		depends on VIDEO_RDACM20 || VIDEO_RDACM21 

You should *not* never do:

 	depends on VIDEO_MAX9271_SERIALIZER || !VIDEO_MAX9271_SERIALIZER
	
for VIDEO_RDACM20 or VIDEO_RDACM21, as it would cause a dependency
loop.

-

If you do, instead:

    if VIDEO_V4L2 && I2C
	config VIDEO_MAX9271_SERIALIZER
		tristate

	config VIDEO_RDACM20
		select VIDEO_MAX9271_SERIALIZER
		...

	config VIDEO_RDACM21
		select VIDEO_MAX9271_SERIALIZER
		...
    endif

Then you also won't need:
	depends on VIDEO_MAX9271_SERIALIZER || !VIDEO_MAX9271_SERIALIZER

As select should do the right thing in this case, ensuring that MAX9271
will be builtin either if RDACM20 or RDACM21 is builtin.

-

This should also work:

	config VIDEO_MAX9271_SERIALIZER
		tristate
		...

	if VIDEO_MAX9271_SERIALIZER

	config VIDEO_RDACM20
		tristate
		...

	config VIDEO_RDACM21
		tristate
		...

	endif

without needing a "depend on FOO || !FOO" logic, but, as I said before, this 
case will force the user that want to build the RDACM20/RDACM21 drivers to 
be aware that a MAX9271 driver is required.

-

You would only need a "depend on FOO || !FOO" if the driver FOO is
optional and if you try do something like:

	config FOO
		tristate
		...

	config VIDEO_RDACM20
		tristate
		depends on FOO
		...

	config VIDEO_RDACM21
		tristate
		depends on FOO
		...
	
as, on such case, it would allow the vars to be:
	
	FOO="m"
	VIDEO_RDACM20="y"
	VIDEO_RDACM21="m"

which would cause build errors.

Thanks,
Mauro