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

From: Sakari Ailus <[email-masked]>
Date: Mon, 8 Feb 2021 11:24:25 +0200

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 <[email-masked]> 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 <[email-masked]>
> > > > > Fixes: a59f853b3b4b ("media: i2c: Add driver for RDACM21 camera module")
> > > > > Signed-off-by: Mauro Carvalho Chehab <[email-masked]>
> > > > > ---
> > > > >  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

> 
> > 
> > Also, as select does not handle dependencies, all drivers that need MAX9271
> > would have to include the dependencies of MAX9271.
> 
> Yes. "Depends on" handles any dependencies that are required for building
> MAX9271. In this specific case, the dependencies are the same, so select
> could equally work.

Sure.

-- 
Kind regards,

Sakari Ailus