Re: [PATCH] drivers: Let several drivers depends on HAS_IOMEM for 'devm_ioremap_resource'

[Lars-Peter Clausen]

On 07/13/2014 04:03 PM, Richard Weinberger wrote:
> Am 13.07.2014 15:56, schrieb Lars-Peter Clausen:
> > On 07/13/2014 03:40 PM, Richard Weinberger wrote:
> > > Am 13.07.2014 15:26, schrieb Lars-Peter Clausen:
> > > > On 07/13/2014 11:45 AM, Richard Weinberger wrote:
> > > > > Am 13.07.2014 11:27, schrieb Lennox Wu:
> > > > > > As I said before, some configurations don't make sense.
> > > > >
> > > > > If such a configuration can be achieved using allmod/yesconfig it has to be fixed.
> > > > > Chen's fixes seem reasonable as not all architectures support iomem.
> > > >
> > > > Maybe we should stub out ioremap() and friends when COMPILE_TEST is enabled to avoid these linker errors. That's in my opinion better than turning most of the 'depends on
> > > > COMPILE_TEST' into 'depends on COMPILE_TEST && HAS_IOMEM'. The issue comes up quite a lot and it is often overlooked when adding a driver that can be build when COMPILE_TEST is
> > > > enabled.
> > >
> > > And what should this stub do?
> > > Except calling BUG()...
> >
> > return NULL;
> >
> > It's for compile testing, it's not meant to work at runtime.
>
> Hm, I really don't like the idea of having a non-working kernel.
> IMHO either it should build _and_ run and nothing else.
> Greg, what do you think?

The kernel will still be working fine and you can run it on a system. The 
drivers which use ioremap() or similar are probably not instantiated on a 
system that does not provide HAS_IOMEM. But even if it was the driver should 
handle ioremap() returning NULL gracefully and abort the driver probe. That 
said you'll probably not run a kernel that was built with COMPILE_TEST on your 
real hardware since it contains so many drivers that are completely useless on 
your hardware. The idea of COMPILE_TEST is to have as much compile test 
exposure as possible to the code that is enabled by COMPILE_TEST. Stubbing out 
ioremap() and friends when HAS_IOMEM is not set and COMPILE_TEST is set makes 
it easier to get there.

- Lars

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