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

From: Sakari Ailus <[email-masked]>
Date: Mon, 8 Feb 2021 11:03:26 +0200

On Mon, Feb 08, 2021 at 09:59:07AM +0100, Jacopo Mondi wrote:
> Hi Sakari,
> 
> On Mon, Feb 08, 2021 at 10:41:47AM +0200, Sakari Ailus wrote:
> > 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.
> > > >
> > >
> > > 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.
> 
> Shouldn't other camera modules that include such serializer select its
> symbol then ?
> 
> >
> > Also, as select does not handle dependencies, all drivers that need MAX9271
> > would have to include the dependencies of MAX9271.
> >
> 
> Wouldn't select just select the MAX9271 symbol, which will list its own
> dependencies ?

You can have anything there but it'll be ignored.

Documentation/kbuild/kconfig-language.rst:

        select should be used with care. select will force
        a symbol to a value without visiting the dependencies.

> 
> 
> > >
> > > > >  #
> > > > >  # V4L2 I2C drivers that are related with Camera support
> > > > >  #
> > > > > diff --git a/drivers/media/i2c/Makefile b/drivers/media/i2c/Makefile
> > > > > index 6bd22d63e1a7..63bb16e51876 100644
> > > > > --- a/drivers/media/i2c/Makefile
> > > > > +++ b/drivers/media/i2c/Makefile
> > > > > @@ -125,10 +125,10 @@ obj-$(CONFIG_VIDEO_IMX319)	+= imx319.o
> > > > >  obj-$(CONFIG_VIDEO_IMX334)	+= imx334.o
> > > > >  obj-$(CONFIG_VIDEO_IMX355)	+= imx355.o
> > > > >  obj-$(CONFIG_VIDEO_MAX9286)	+= max9286.o
> > > > > -rdacm20-camera_module-objs	:= rdacm20.o max9271.o
> > > > > -obj-$(CONFIG_VIDEO_RDACM20)	+= rdacm20-camera_module.o
> > > > > -rdacm21-camera_module-objs	:= rdacm21.o max9271.o
> > > > > -obj-$(CONFIG_VIDEO_RDACM21)	+= rdacm21-camera_module.o
> > > > > +obj-$(CONFIG_VIDEO_RDACM20)	+= rdacm20.o
> > > > > +obj-$(CONFIG_VIDEO_RDACM21)	+= rdacm21.o
> > > > >  obj-$(CONFIG_VIDEO_ST_MIPID02) += st-mipid02.o
> > > > >
> > > > > +obj-$(CONFIG_VIDEO_MAX9271_SERIALIZER) += max9271.o
> > > > > +
> > > > >  obj-$(CONFIG_SDR_MAX2175) += max2175.o
> > > >
> > > > --
> > > > Kind regards,
> > > >
> > > > Sakari Ailus
> >
> > --
> > Sakari Ailus

-- 
Sakari Ailus