Re: Looking for good references for ARM driver development

From: Mason
Date: Wed Nov 19 2014 - 11:08:47 EST

Hello Andreas,

On 19/11/2014 16:02, Andreas Färber wrote:

Am 19.11.2014 um 13:50 schrieb Mason:

[...] I'm writing a driver for a temperature sensor, which is
supposed to work within the hwmon/lm-sensors framework.

The sensor's API consists of 3 memory-mapped registers, which are
accessible over the SoC's memory bus. [...]

1) Which bus should I be using for this driver?
Is the platform bus appropriate?


Is there an exhaustive list of available buses (on the ARM platform)
and an overview of when/where each one is appropriate?

2) platform.txt states

Some drivers are not fully converted to the driver model, because
they take on a non-driver role: the driver registers its
platform device, rather than leaving that for system
infrastructure. Such drivers can't be hotplugged or coldplugged,
since those mechanisms require device creation to be in a
different system component than the driver.

How do I "leave device registration for the system
infrastructure"? Where should I put that code? Is it a good idea to
separate device registration and driver registration in the case of
a SoC, where the device is embedded in the SoC and is not
"hot-plugged" (or anything-plugged for that matter, it's just

Since this appears to be about an ARM SoC according to your To list,
in general, you create a device tree binding, that binding is
registered within your platform/... driver code and referenced in the
device tree for SoC or board, and then your driver will automatically
be probed.

I know nothing about DT (aside from the Wikipedia entry).
I'll take a closer look at Documentation/devicetree.
Will that explain what platform/... is?

I see a drivers/platform folder, but nothing ARM-specific there?

4) Can I use platform_driver_probe, instead of

Most likely you do not need to call either yourself.

Hmmm, color me even more confused. I had really come to believe that
driver registration was a mandatory part of the driver, something
that wasn't left to "infrastructure code".

Just compare other platform drivers on the one hand, and temperature
sensor drivers on the other (such as I2C based gmt,g781 / LM90). Did
you already check whether there is a driver that is both?

Please excuse my naive question: what are platform drivers, and where
are they stored in the kernel source tree?


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