linux-kernel - Re: [PATCH] Input: atmel_mxt_ts: Add of node type to the i2c table

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Date:	Thu, 11 Sep 2014 13:08:29 +0200
From:	Wolfram Sang <wsa@...-dreams.de>
To:	Nick Dyer <nick.dyer@...ev.co.uk>
Cc:	Javier Martinez Canillas <javier.martinez@...labora.co.uk>,
	Sjoerd Simons <sjoerd.simons@...labora.co.uk>,
	Lee Jones <lee.jones@...aro.org>,
	Dmitry Torokhov <dmitry.torokhov@...il.com>,
	linux-input@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-samsung-soc@...r.kernel.org,
	"Bowens, Alan" <Alan.Bowens@...el.com>
Subject: Re: [PATCH] Input: atmel_mxt_ts: Add of node type to the i2c table


Funny timing. I am just reviewing the series from Lee and also stumbled
over modaliases, too...

On Thu, Sep 11, 2014 at 10:19:54AM +0100, Nick Dyer wrote:
> On 11/09/14 09:38, Javier Martinez Canillas wrote:
> > To expand on what Sjoerd already said and just to be sure everyone is on the
> > same page.
> > 
> > The problem is that right now the driver reports the following modalias:
> > 
> > # cat /sys/class/i2c-adapter/i2c-8/8-004b/modalias
> > i2c:maxtouch
> > 
> > but if you look at the module information, that is not a valid alias:
> > 
> > # modinfo atmel_mxt_ts | grep alias
> > alias:          i2c:mXT224
> > alias:          i2c:atmel_mxt_tp
> > alias:          i2c:atmel_mxt_ts
> > alias:          i2c:qt602240_ts
> > alias:          of:N*T*Catmel,maxtouch*
> > 
> > which means that udev/kmod can't load the module automatically based on the
> > alias information.
> > 
> > The aliases are filled by both MODULE_DEVICE_TABLE(i2c, mxt_id) and
> > MODULE_DEVICE_TABLE(of, mxt_of_match) so after Sjoerd's patch:
> > 
> > # cat /sys/class/i2c-adapter/i2c-8/8-004b/modalias
> > i2c:maxtouch
> > 
> > # modinfo atmel_mxt_ts | grep alias
> > alias:          i2c:mXT224
> > alias:          i2c:maxtouch
> > alias:          i2c:atmel_mxt_tp
> > alias:          i2c:atmel_mxt_ts
> > alias:          i2c:qt602240_ts
> > 
> > which matches the reported uevent so the module will be auto-loaded.
> > 
> > This is because the I2C subsystem hardcodes i2c:<client->name>, if you look at
> > drivers/i2c/i2c-core.c:
> > 
> > /* uevent helps with hotplug: modprobe -q $(MODALIAS) */
> > static int i2c_device_uevent(struct device *dev, struct kobj_uevent_env *env)
> > {
> > ...
> >         if (add_uevent_var(env, "MODALIAS=%s%s",
> >                            I2C_MODULE_PREFIX, client->name))
> > ...
> > }
> > 
> > I've looked at Lee's series and AFAICT that remains the same so I second
> > Sjoerd that module auto-loading will continue to be broken.

I think the above code in the i2c core needs a fix. Will have a closer
look after lunch.

> The i2c aliases are a bit confusing. The original device the driver was
> written for was called qt602240, which was renamed by Atmel to mXT224 when
> the chip series was called "maXTouch". The driver now actually supports
> many other chips which aren't listed (more than 20 devices that I've
> personally tested). I could add them all, but it would be an extremely long
> list. It may be preferable to use the generic name maXTouch.

This is probably true for some more I2C devices. Like RTCs being
compatible or, most prominent, EEPROMS. I don't want to have a list of
all vendors producing 24c02s if they are all compatible. If generic
entries are frowned upon, I'd agree on a "first come, first served" policy:
Somebody provides one compatible-property with the vendor which happens
to be on that board, and the others have to reuse that
compatible-property since they are, well, compatible.

> So I think the sensible thing to do here would be to add "maxtouch" to the
> i2c list to fix the module autoload issue.

This is a workaround. It would make sense, however, to add it because we
want to support i2c_board_info structures.

Regards,

   Wolfram


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