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

From: Laurent Pinchart <[email-masked]>
Date: Mon, 8 Feb 2021 15:40:10 +0200

Hi Mauro,

On Mon, Feb 08, 2021 at 02:31:50PM +0100, Mauro Carvalho Chehab wrote:
> Em Mon, 8 Feb 2021 14:11:02 +0100 Mauro Carvalho Chehab escreveu:
> > Em Mon, 8 Feb 2021 12:41:42 +0100 Jacopo Mondi escreveu:
> > 
> > > > > 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.  
> > > >
> > > > I also vote for usage of "select".
> > > >  
> > > 
> > > I would prefer that too, I was concerned about possible un-met
> > > dependencies, as Sakari pointed out, but the current situation is no
> > > better, as the only Kconfig symbols where those can be listed are the
> > > camera modules one.
> > 
> > Works for me. I'll make a patch for it.
> 
> Hmm... after taking a deeper look at the rcma20 drivers, and on its
> Kconfig help text:
> 
> 	config VIDEO_RDACM20
> 		tristate "IMI RDACM20 camera support"
> 		select V4L2_FWNODE
> 		select VIDEO_V4L2_SUBDEV_API
> 		select MEDIA_CONTROLLER
> 		help
> 		  This driver supports the IMI RDACM20 GMSL camera, used in
> 		  ADAS systems.
> 
> 		  This camera should be used in conjunction with a GMSL
> 		  deserialiser such as the MAX9286.
> 
> I'm starting to suspect that there's something very wrong here...
> 
> The help text mentions the MAX9286 driver, which is a complete
> driver, and not MAX9271, which seems to implement a set of PHY functions
> needed by those drivers, and which lacks a proper I2C binding code on it.
> 
> The I2C binding code is, instead, inside RDACM20 and RDACM21:
> 
> 	static int rdacm21_initialize(struct rdacm21_device *dev)
> 	{
> 		int ret;
> 
> 		/* Verify communication with the MAX9271: ping to wakeup. */
> 		dev->serializer.client->addr = MAX9271_DEFAULT_ADDR;
> 		i2c_smbus_read_byte(dev->serializer.client);
> 		usleep_range(3000, 5000);
> 
> 		/* Enable reverse channel and disable the serial link. */
> 		ret = max9271_set_serial_link(&dev->serializer, false);
> 		if (ret)
> 			return ret;
> 
> 		/* Configure I2C bus at 105Kbps speed and configure GMSL. */
> 		ret = max9271_configure_i2c(&dev->serializer,
> 					    MAX9271_I2CSLVSH_469NS_234NS |
> 					    MAX9271_I2CSLVTO_1024US |
> 					    MAX9271_I2CMSTBT_105KBPS);
> 
> 		/* Several other max9271-specific init code */
> 
> 		ret = ov490_initialize(dev);
> 		if (ret)
> 			return ret;
> 
> And, at max9271 "driver", there's just a bunch of exported functions.
> 
> This is all wrong.
> 
> I'm seriously considering to move all those 3 drivers to staging,
> while they're not fixed to use a proper I2C binding mechanism.

They can't. The RDACM20 and RDACM21 are GMSL cameras, that are
internally made of a GMSL serializer (MAX9271 in both cases) and a
camera sensor (OV10625 for the RDACM20, OV10640 + OV490 ISP for the
RDAMC21). The sensor and serializer are tightly couple, so much so that
in the RDACM20, there's a microcontroller that configures both when
power is applied. In the RDACM21, the OV490 firmware has a similar role.
Due to the tight coupling and the presense of a device-specific
microcontroller, the cameras need to be handled as a whole, we can't
have one driver for the sensor and one driver for the serializer that
would work in isolation and be controlled separately from userspace. The
MAX9271, however, still needs to be configured from the host, and we've
thus moved common code to a common file instead of duplicating it.

-- 
Regards,

Laurent Pinchart