linux-kernel - Re: [PATCH] tools: iio: add ability to pass kernel headers

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Date:   Thu, 20 Apr 2017 19:23:11 +0530
From:   Sekhar Nori <nsekhar@...com>
To:     Jonathan Cameron <jic23@...nel.org>,
        Randy Dunlap <rdunlap@...radead.org>
CC:     Hartmut Knaack <knaack.h@....de>,
        Lars-Peter Clausen <lars@...afoo.de>,
        Peter Meerwald-Stadler <pmeerw@...erw.net>,
        <linux-iio@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] tools: iio: add ability to pass kernel headers

On Tuesday 18 April 2017 03:42 PM, Sekhar Nori wrote:
> Hi Jonathan, Randy,
> 
> On Friday 14 April 2017 08:53 PM, Jonathan Cameron wrote:
>> On 14/04/17 16:23, Randy Dunlap wrote:
>>> On 04/14/17 07:42, Jonathan Cameron wrote:
>>>> On 11/04/17 12:06, Sekhar Nori wrote:
>>>>> Very often, especially when cross compiling, there is a need
>>>>> to pass kernel headers different from those installed on the
>>>>> build machine.
>>>>>
>>>>> Add support for doing this for iio utils by using the
>>>>> 'INSTALL_HDR_PATH' environment variable. This is supported by
>>>>> 'make headers_install' for installing kernel headers at a
>>>>> user specified location. So you will do:
>>>>>
>>>>> $ make headers_install ARCH=arm INSTALL_HDR_PATH=<absolute-path>
>>>>> $ make -C tools/iio ARCH=arm INSTALL_HDR_PATH=<absolute-path>
>>>>>
>>>>> Signed-off-by: Sekhar Nori <nsekhar@...com>
>>>>
>>>> It's a bit of an oddity as that usually refers to where to put
>>>> the headers rather than where they are.
>>>>
>>>> Is there a more general solution?  I couldn't find anything
>>>> particularly consistent in tools.
>>>
>>> Whatever the solution is, it should be used for all tools/, not just iio.
>>>
>> Agreed!
> 
> Alright, I will try to come up with something more generic and post
> another version.

I have been looking at this, and coming up with something generic is
more complicated than I thought. The problem is the flexibility thats
allowed in building many of the tools. For example, you can build the
led tools using any of these three methods:

$ make -C <kernelsrcdir> tools/leds
$ make -C <kernelsrcdir>/tools leds
$ make -C <kernelsrcdir>/tools/leds

The last one is specifically complicated because it totally bypasses all
top level makefiles. I think adding dependency with a top level makefile
will be a step backwards at least for leds.

Currently the leds makefile adds '-I../../include/uapi' to CFLAGS to
access the latest kernel headers. Something similar is done for some
other tools too. This makes it work for all the build cases above. I
propose we do something similar for iio too.

Thanks,
Sekhar