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Subject: Re: [PATCH] tools: iio: add ability to pass kernel headers
To: Jonathan Cameron <jic23@kernel.org>,
        Randy Dunlap <rdunlap@infradead.org>
References: <d5f344548931389ea4598be946bdc28af1790cc9.1491908438.git.nsekhar@ti.com>
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CC: Hartmut Knaack <knaack.h@gmx.de>, Lars-Peter Clausen <lars@metafoo.de>,
        Peter Meerwald-Stadler <pmeerw@pmeerw.net>,
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From: Sekhar Nori <nsekhar@ti.com>
Message-ID: <b59f1267-b30e-4c64-0a93-8f75b17fcdfb@ti.com>
Date: Thu, 20 Apr 2017 19:23:11 +0530
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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@ti.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