[linux-sunxi] Re: [PATCH] ARM: dts: sun4i: Add dts file for the pov protab2-ips9 tablet

On Tue, Sep 08, 2015 at 09:48:48AM +0200, Hans de Goede wrote:

Hi,

On 07-09-15 22:52, Maxime Ripard wrote:

quoted

Hi,

On Mon, Sep 07, 2015 at 11:30:03AM +0200, Hans de Goede wrote:

quoted

quoted

quoted

quoted

bma250 already has devicetree support. It is used in Gemei G9
tablet (sun4i-gemei-g9.dts).

Yes I've seen that, but does it actually work? I've not tried but
I do not see any compatible string in the actual bma250 code in
the kernel, so I believe that this part of the sun4i-gemei-g9.dts
file does not work ?

It worked (even without IRQs) when I submitted the patch. Driver
itself is under iio/accel/bma180.c

That is really weird, because:

https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/drivers/iio/accel/bma180.c

Does not have an of_match_table ... ??

Not really, when using DT, i2c will set the i2c_client name to the
device part of the compatible [1] [2], and then if the of_device_id
lookup fails, will fallback to matching the i2c_client name to the
i2c_device_id [3]. Which in our case matches.

Maxime

[1] http://lxr.free-electrons.com/source/drivers/i2c/i2c-core.c#L1281
[2] http://lxr.free-electrons.com/source/drivers/i2c/i2c-core.c#L969
[3] http://lxr.free-electrons.com/source/drivers/i2c/i2c-core.c#L461

Hmm, not sure whether that is a useful feature or an ugly hack :)

Don't shoot the messenger :)

But I don't know either.

It is sorta unexpected either way. But I can make good use of this to
enable the accelerometer and maybe also some touchscreens on a bunch of
boards I have.

Still should we rely on this? This means relying on Linux kernel behavior,
rather then something documented in Documentation/devicetree/bindings/...

AFAIK, the behaviour isn't going away, there's been a few patches to
remove the need for i2c_device_id, and they've all been nacked, so I'd
say we can use it as is.

Maxime

-- 
Maxime Ripard, Free Electrons
Embedded Linux, Kernel and Android engineering
http://free-electrons.com
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