Em Tue, 26 Jan 2016 16:53:38 +0100
Arnd Bergmann [off-list ref] escreveu:

On Tuesday 26 January 2016 12:33:08 Mauro Carvalho Chehab wrote:

quoted

Em Tue, 26 Jan 2016 15:10:00 +0100
Arnd Bergmann [off-list ref] escreveu:
  

quoted

em28xx selects VIDEO_TUNER, which has a dependency on MEDIA_TUNER,
so we get a Kconfig warning if that is disabled:

warning: (VIDEO_PVRUSB2 && VIDEO_USBVISION && VIDEO_GO7007 && VIDEO_AU0828_V4L2 && VIDEO_CX231XX && VIDEO_TM6000 && VIDEO_EM28XX && VIDEO_IVTV && VIDEO_MXB && VIDEO_CX18 && VIDEO_CX23885 && VIDEO_CX88 && VIDEO_BT848 && VIDEO_SAA7134 && VIDEO_SAA7164) selects VIDEO_TUNER which has unmet direct dependencies (MEDIA_SUPPORT && MEDIA_TUNER)  

This warning is bogus, as it is OK to select VIDEO_TUNER even if MEDIA_TUNER
is not defined.

See how MEDIA_TUNER is defined:


config MEDIA_TUNER
	tristate
	depends on (MEDIA_ANALOG_TV_SUPPORT || MEDIA_DIGITAL_TV_SUPPORT || MEDIA_RADIO_SUPPORT || MEDIA_SDR_SUPPORT) && I2C
	default y
	select MEDIA_TUNER_XC2028 if MEDIA_SUBDRV_AUTOSELECT
	select MEDIA_TUNER_XC5000 if MEDIA_SUBDRV_AUTOSELECT
	select MEDIA_TUNER_XC4000 if MEDIA_SUBDRV_AUTOSELECT
	select MEDIA_TUNER_MT20XX if MEDIA_SUBDRV_AUTOSELECT
	select MEDIA_TUNER_TDA8290 if MEDIA_SUBDRV_AUTOSELECT
	select MEDIA_TUNER_TEA5761 if MEDIA_SUBDRV_AUTOSELECT && MEDIA_RADIO_SUPPORT
	select MEDIA_TUNER_TEA5767 if MEDIA_SUBDRV_AUTOSELECT && MEDIA_RADIO_SUPPORT
	select MEDIA_TUNER_SIMPLE if MEDIA_SUBDRV_AUTOSELECT
	select MEDIA_TUNER_TDA9887 if MEDIA_SUBDRV_AUTOSELECT
	select MEDIA_TUNER_MC44S803 if MEDIA_SUBDRV_AUTOSELECT

MEDIA_TUNER is just one of the media Kconfig workarounds to its limitation of
not allowing to select a device that has dependencies. It is true if the user
selected either TV or radio media devices. It works together with 
MEDIA_SUBDRV_AUTOSELECT. When both are enabled, it selects all
media tuners. That makes easier for end users to not need to worry about
manually selecting the needed tuners.

Advanced users may, instead, manually select the media tuner that his
hardware needs. In such case, it doesn't matter if MEDIA_TUNER
is enabled or not.

As this is due to a Kconfig limitation, I've no idea how to fix or get
hid of it, but making em28xx dependent of MEDIA_TUNER is wrong.  

I don't understand what limitation you see here. 

Before MEDIA_TUNER, what we had was something like:

	config MEDIA_driver_foo
	select VIDEO_tuner_bar if MEDIA_SUBDRV_AUTOSELECT
	select MEDIA_frontend_foobar if MEDIA_SUBDRV_AUTOSELECT
	...

However, as different I2C drivers had different dependencies, this
used to cause lots of troubles. So, one of the Kbuild maintainers
came out with the idea of converting from select into depends on.
The MEDIA_TUNER is just an ancillary invisible option to make it
work at the tuner's side, as usually what we want is to have all
tuners selected, as we don't have a one to one mapping about what
driver supports what tuner (nor we wanted to do it, as this would
mean lots of work for not much gain).

The definition
of the VIDEO_TUNER symbol is an empty 'tristate' symbol with a
dependency on MEDIA_TUNER to ensure we get a warning if MEDIA_TUNER
is not enabled, and to ensure it is set to 'm' if MEDIA_TUNER=m and
a "bool" driver selects VIDEO_TUNER.

No, VIDEO_TUNER is there because we wanted to be able to use select
to enable V4L2 tuner core support and let people to manually select
the needed I2C devices with MEDIA_SUBDRV_AUTOSELECT unselected.

Doesn't need to worry about that, because all drivers that select VIDEO_TUNER
depend on I2C:

drivers/media/pci/bt8xx/Kconfig:        select VIDEO_TUNER
drivers/media/pci/cx18/Kconfig: select VIDEO_TUNER
drivers/media/pci/cx23885/Kconfig:      select VIDEO_TUNER
drivers/media/pci/cx88/Kconfig: select VIDEO_TUNER
drivers/media/pci/ivtv/Kconfig: select VIDEO_TUNER
drivers/media/pci/saa7134/Kconfig:      select VIDEO_TUNER
drivers/media/pci/saa7146/Kconfig:      select VIDEO_TUNER
drivers/media/pci/saa7164/Kconfig:      select VIDEO_TUNER
drivers/media/usb/au0828/Kconfig:       select VIDEO_TUNER
drivers/media/usb/cx231xx/Kconfig:      select VIDEO_TUNER
drivers/media/usb/em28xx/Kconfig:       select VIDEO_TUNER
drivers/media/usb/go7007/Kconfig:       select VIDEO_TUNER
drivers/media/usb/pvrusb2/Kconfig:      select VIDEO_TUNER
drivers/media/usb/tm6000/Kconfig:       select VIDEO_TUNER
drivers/media/usb/usbvision/Kconfig:    select VIDEO_TUNER

This will always be the case for PCI/USB drivers that support analog TV,
as those drivers need to implement the I2C adapter code inside them.

Yes, the above could work. This is simpler fix, and should work fine for
all current usecases:

diff --git a/drivers/media/v4l2-core/Kconfig b/drivers/media/v4l2-core/Kconfig
index 9beece00869b..b30e1c879a57 100644
--- a/drivers/media/v4l2-core/Kconfig
+++ b/drivers/media/v4l2-core/Kconfig

@@ -37,7 +37,7 @@ config VIDEO_PCI_SKELETON
 # Used by drivers that need tuner.ko
 config VIDEO_TUNER
 	tristate
-	depends on MEDIA_TUNER
+	default MEDIA_TUNER
 
 # Used by drivers that need v4l2-mem2mem.ko
 config V4L2_MEM2MEM_DEV

Ok, if we'll have platform drivers for analog TV using the I2C bus
at directly in SoC, then your solution is better, but the tuner core
driver may not be the best way of doing it. So, for now, I would use
the simpler version.

Regards,
Mauro