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 13:24:55 +0200
From:	Javier Martinez Canillas <javier.martinez@...labora.co.uk>
To:	Wolfram Sang <wsa@...-dreams.de>, Nick Dyer <nick.dyer@...ev.co.uk>
CC:	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

Hello Wolfram,

On 09/11/2014 01:08 PM, Wolfram Sang wrote:
> 
> 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.
> 

Agreed, I just posted an RFC patch [0] with the fix but as Sjoerd pointed out
on an internal review, changing that will regress all the drivers that were
relying on the old behavior.

>> 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.
> 

Agreed.

>> 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.
> 

I think it really depends if an IP block can be used on non-DT platforms
(which I think is true for this trackpad) but if a driver is for an IP block
that can only be used on a DT-only platform (e.g: a PMIC that is controlled
over I2C and is only compatible with a DT-only SoC) then I don't think we need
to support the i2c_board_info structure and can get rid of the I2C ID table on
these drivers once Lee series land.

> Regards,
> 
>    Wolfram
> 

Best regards,
Javier

[0]: https://patchwork.ozlabs.org/patch/388200/
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