Re: [ptxdist] target package dependency to platform

[Michael Olbrich <m.olbrich@pengutronix.de>]

Hi,

On Tue, Jan 31, 2023 at 04:33:00PM +0100, Alexander Dahl wrote:
> I'm stuck with a problem where I can not find an elegant solution for.  
> Let me describe.
> 
> I have a layered BSP.  The base layer has different platformconfigs for 
> hardware targets with different SoC architectures, let's say the 
> PTXCONF_PLATFORM is "pla" on one and "plb" on the other.  (I can not build the 
> whole stuff for one platform only, two platforms are strictly required.)
> 
> There is a more or less ordinary CMake based target application in the base 
> layer, let's say in "base/rules/myapp.{in,make}", because that application is 
> needed on both platforms.
> 
> The two upper layers select the different platforms with different toolchains 
> and both also enable "myapp".  (Yes, I could also have it all in a single 
> layer BSP with two working copies and building one platform per working copy.  
> Doesn't change the problem.)
> 
> myapp depends on multiple libraries, some of them hardware specific.  So for 
> platform "pla" it needs "libmyliba" and for platform "plb" it does not.
> 
> In "base/rules/myapp.make" I pass PTXCONF_PLATFORM as a build time option to 
> CMake like this:
> 
>     MYAPP_CONF_OPT += -DHARDWARE_NAME=$(PTXCONF_PLATFORM)
> 
> Depending on "HARDWARE_NAME" I call `find_package(myliba)` in "CMakeLists.txt" 
> of myapp.
> 
> I could do a "select LIBMYLIBA" in "base/rules/myapp.in" unconditionally, and 
> that would make the build successful.  In the BSP for platform "pla" CMake 
> would look for libmyliba and link and on the target it would be used at 
> runtime just fine.  In the BSP for platform "plb" CMake would not look for it, 
> would not complain, myapp would run happily on the target without using 
> libmyliba just fine.
> 
> However, libmyliba would be built for platform "plb" and it would be copied 
> over to "plb" target and take space, but never be used there.  Build time for 
> it would be completely wasted.  Even worse, user might find it on target and 
> wonder what it means, although it's useless on platform "plb".
> 
> I could _not_ add that "select LIBMYLIBA" and build would fail for target 
> "pla" dependending on package build order.  Also dependencies in opkg packages 
> would not be correct then.
> 
> What also does not work is this (in "base/rules/myapp.in"):
> 
>     select LIBMYLIBA if PLATFORM = "pla"
> 
> This is valid syntax from Kconfig point of view, but PLATFORM is just not 
> defined here at all.  I assume configs/ptxconfig and configs/platform-pla/
> platformconfig are somewhat distinct Kconfig spaces and one can not simply 
> reference to Kconfig options from the other side.
> 
> Interestingly I can do `ptxdist print PTXCONF_PLATFORM` and `ptxdist print 
> PTXCONF_MYAPP` and ptxdist prints variables from both Kconfig spaces.  Also I 
> can successfully use both in base/rules/myapp.make and that's at least 
> somewhat misleading. (Misleading as in: Why can I use both here but not 
> there?)
> 
> That's where I'm stuck.  Of course I looked through ptxdist git sources to 
> find hints on how to solve this dilemma, but without luck.
> 
> Would be happy if anyone could give a hint or suggest a solution.

You can add the dependency in just one layer:
Either copy myapp.in to rules/myapp.in in that layer and add the dependency
or (if that file is sufficiently complex), create rules/myapp.fixup.in
with:
-------------------------------------------
## SECTION=....

config MYAPP
	select LIBMYLIBA
-------------------------------------------
Kconfig will basically just merge the two entries internally.

Then run "ptxdist oldconfig" in that layer. You'll get a modified ptxconfig
and a ptxconfig.diff with just PTXCONF_LIBMYLIBA=y (and comments).
You'll need to run oldconfig whenever the base ptxconfig changes. PTXdist
will complain if they are out of sync.

This is one of the use-cases I had in mind when I designed the layers in
PTXdist.

Michael

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