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

Greg Kroah-Hartman
2014-07-13T20:17:53Z

On Sun, Jul 13, 2014 at 09:33:38PM +0200, Richard Weinberger wrote:
> Am 13.07.2014 21:22, schrieb Greg Kroah-Hartman:
> > On Sun, Jul 13, 2014 at 04:25:06PM +0200, Lars-Peter Clausen wrote:
> >> 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.
> >
> > I run my kernels with COMPILE_TEST enabled as I need to build test
> > things that I don't happen to use.
> >
> > I like the 'return NULL' option for this, it hits us all the time, might
> > as well fix it properly like this so that we don't have to deal with
> > Kconfig changes everywhere.
> >
> > Also put a big "This platform does not support IOMEM" error printk in
> > there, so that people have a chance to figure out what is going on if
> > they happen to run such a driver on a platform that can't support it.
>
> Maybe we could add COMPILE_TEST to the version string too?
> Just to detect such kernels fast in user bug reports...

What kind of bug report are you going to get?