nommu build failures on ARM in linux-next

nommu build failures on ARM in linux-next

[Paul Gortmaker]

Hi Russell,

The allnoconfig builds in linux-next fail because __clear_cr
lives in mmu.c without any stub or similar in nommu.c

Introduced by:

commit 247e4fff3aa927ad069447e6da05bb966b70dece
Author: Russell King <rmk+kernel@arm.linux.org.uk>
Date:   Sun Apr 13 18:57:29 2014 +0100

    ARM: provide common method to clear bits in CPU control register
    
Sample failure:
  http://kisskb.ellerman.id.au/kisskb/buildresult/11264405/

Paul.

nommu build failures on ARM in linux-next

[Russell King - ARM Linux]

On Thu, May 29, 2014 at 12:53:51PM -0400, Paul Gortmaker wrote:
> Hi Russell,
> 
> The allnoconfig builds in linux-next fail because __clear_cr
> lives in mmu.c without any stub or similar in nommu.c
> 
> Introduced by:
> 
> commit 247e4fff3aa927ad069447e6da05bb966b70dece
> Author: Russell King <rmk+kernel@arm.linux.org.uk>
> Date:   Sun Apr 13 18:57:29 2014 +0100
> 
>     ARM: provide common method to clear bits in CPU control register
>     
> Sample failure:
>   http://kisskb.ellerman.id.au/kisskb/buildresult/11264405/

ALIGNMENT_TRAP depends on CPU_CP15_MMU, so it's quite reasonable that
__clear_cr should exist in this case - but it doesn't because it's in
mmu.c.  I guess we need __clear_cr moved to arch/arm/kernel/setup.c.

-- 
FTTC broadband for 0.8mile line: now at 9.7Mbps down 460kbps up... slowly
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nommu build failures on ARM in linux-next

[Russell King - ARM Linux]

On Thu, May 29, 2014 at 07:55:34PM +0100, Russell King - ARM Linux wrote:
> On Thu, May 29, 2014 at 12:53:51PM -0400, Paul Gortmaker wrote:
> > Hi Russell,
> > 
> > The allnoconfig builds in linux-next fail because __clear_cr
> > lives in mmu.c without any stub or similar in nommu.c
> > 
> > Introduced by:
> > 
> > commit 247e4fff3aa927ad069447e6da05bb966b70dece
> > Author: Russell King <rmk+kernel@arm.linux.org.uk>
> > Date:   Sun Apr 13 18:57:29 2014 +0100
> > 
> >     ARM: provide common method to clear bits in CPU control register
> >     
> > Sample failure:
> >   http://kisskb.ellerman.id.au/kisskb/buildresult/11264405/
> 
> ALIGNMENT_TRAP depends on CPU_CP15_MMU, so it's quite reasonable that
> __clear_cr should exist in this case - but it doesn't because it's in
> mmu.c.  I guess we need __clear_cr moved to arch/arm/kernel/setup.c.

I've been looking at doing this, and while it can be done by applying
a patch on top, that's not my preferred solution.

However, my preferred solution (which is to fix the commit) needs a bit
of rework of the patch series, and given the number of patches I'm
carrying right now, I'm just going to drop the branch out of linux-next
and hold it off until the following merge window instead.

Even so, I suspect even with this build problem solved, that's not going
to be the end of the story for noMMU breakage... it's certainly something
that gets very little testing by anyone.  I suspect it should be removed
from the mainline kernel tree rather than being a constant source of these
kinds of problems.

-- 
FTTC broadband for 0.8mile line: now at 9.7Mbps down 460kbps up... slowly
improving, and getting towards what was expected from it.

nommu build failures on ARM in linux-next

[Paul Gortmaker]

[Re: nommu build failures on ARM in linux-next] On 30/05/2014 (Fri 00:40) Russell King - ARM Linux wrote:

> On Thu, May 29, 2014 at 07:55:34PM +0100, Russell King - ARM Linux wrote:
> > On Thu, May 29, 2014 at 12:53:51PM -0400, Paul Gortmaker wrote:
> > > Hi Russell,
> > > 
> > > The allnoconfig builds in linux-next fail because __clear_cr
> > > lives in mmu.c without any stub or similar in nommu.c
> > > 
> > > Introduced by:
> > > 
> > > commit 247e4fff3aa927ad069447e6da05bb966b70dece
> > > Author: Russell King <rmk+kernel@arm.linux.org.uk>
> > > Date:   Sun Apr 13 18:57:29 2014 +0100
> > > 
> > >     ARM: provide common method to clear bits in CPU control register
> > >     
> > > Sample failure:
> > >   http://kisskb.ellerman.id.au/kisskb/buildresult/11264405/
> > 
> > ALIGNMENT_TRAP depends on CPU_CP15_MMU, so it's quite reasonable that
> > __clear_cr should exist in this case - but it doesn't because it's in
> > mmu.c.  I guess we need __clear_cr moved to arch/arm/kernel/setup.c.
> 
> I've been looking at doing this, and while it can be done by applying
> a patch on top, that's not my preferred solution.
> 
> However, my preferred solution (which is to fix the commit) needs a bit
> of rework of the patch series, and given the number of patches I'm
> carrying right now, I'm just going to drop the branch out of linux-next
> and hold it off until the following merge window instead.
> 
> Even so, I suspect even with this build problem solved, that's not going
> to be the end of the story for noMMU breakage... it's certainly something
> that gets very little testing by anyone.  I suspect it should be removed
> from the mainline kernel tree rather than being a constant source of these
> kinds of problems.

One doesn't have to look very far to see that I'm in favour of pushing
obsolete options/drivers/subsystems off a cliff if I can get away with
it, so that we don't get crushed under our own weight/complexity.

So if you really think it is time for ARM noMMU to go, I'll volunteer to
craft up a removal series for you for 3.17 -- just say the word.

Paul.
--

> 
> -- 
> FTTC broadband for 0.8mile line: now at 9.7Mbps down 460kbps up... slowly
> improving, and getting towards what was expected from it.

nommu build failures on ARM in linux-next

[Robert Schwebel]

On Fri, May 30, 2014 at 12:40:12AM +0100, Russell King - ARM Linux wrote:
> Even so, I suspect even with this build problem solved, that's not going
> to be the end of the story for noMMU breakage... it's certainly something
> that gets very little testing by anyone.  I suspect it should be removed
> from the mainline kernel tree rather than being a constant source of these
> kinds of problems.

Uwe can have a look next week.

Taken that it took *ages* to get Cortex-M3 support in mainline and taken
that it might become more interesting with the upcoming generation of
FPGAs and Cortex-A SoCs with an additional Cortex-M, it would be pretty
bad to lose NOMMU again.

rsc
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nommu build failures on ARM in linux-next

[Uwe Kleine-König]

Hello,

[adding a few people to Cc]

On Fri, May 30, 2014 at 12:40:12AM +0100, Russell King - ARM Linux wrote:
> On Thu, May 29, 2014 at 07:55:34PM +0100, Russell King - ARM Linux wrote:
> > On Thu, May 29, 2014 at 12:53:51PM -0400, Paul Gortmaker wrote:
> > > Hi Russell,
> > > 
> > > The allnoconfig builds in linux-next fail because __clear_cr
> > > lives in mmu.c without any stub or similar in nommu.c
> > > 
> > > Introduced by:
> > > 
> > > commit 247e4fff3aa927ad069447e6da05bb966b70dece
> > > Author: Russell King <rmk+kernel@arm.linux.org.uk>
> > > Date:   Sun Apr 13 18:57:29 2014 +0100
> > > 
> > >     ARM: provide common method to clear bits in CPU control register
> > >     
> > > Sample failure:
> > >   http://kisskb.ellerman.id.au/kisskb/buildresult/11264405/
> > 
> > ALIGNMENT_TRAP depends on CPU_CP15_MMU, so it's quite reasonable that
> > __clear_cr should exist in this case - but it doesn't because it's in
> > mmu.c.  I guess we need __clear_cr moved to arch/arm/kernel/setup.c.
> 
> I've been looking at doing this, and while it can be done by applying
> a patch on top, that's not my preferred solution.
> 
> However, my preferred solution (which is to fix the commit) needs a bit
> of rework of the patch series, and given the number of patches I'm
> carrying right now, I'm just going to drop the branch out of linux-next
> and hold it off until the following merge window instead.
> 
> Even so, I suspect even with this build problem solved, that's not going
> to be the end of the story for noMMU breakage... it's certainly something
> that gets very little testing by anyone.  I suspect it should be removed
> from the mainline kernel tree rather than being a constant source of these
> kinds of problems.
That would mean that support for Cortex-M3 would die, too, which would
(IMHO) be sad.

Currently the efm32 test in our autobuilder is broken, I will address
that and then keep an eye on it.

Best regards
Uwe

-- 
Pengutronix e.K.                           | Uwe Kleine-K?nig            |
Industrial Linux Solutions                 | http://www.pengutronix.de/  |

nommu build failures on ARM in linux-next

[Uwe Kleine-König]

Hello,

On Fri, May 30, 2014 at 10:02:57AM +0200, Uwe Kleine-K?nig wrote:
> > Even so, I suspect even with this build problem solved, that's not going
> > to be the end of the story for noMMU breakage... it's certainly something
> > that gets very little testing by anyone.  I suspect it should be removed
> > from the mainline kernel tree rather than being a constant source of these
> > kinds of problems.
> That would mean that support for Cortex-M3 would die, too, which would
> (IMHO) be sad.
Just for your information: The problem in question here doesn't affect
ARM-v7M (aka Cortex-M[34]) because the patch only touches areas
protected by #ifdef CONFIG_CPU_CP15 which is off for these machines.

Best regards
Uwe

-- 
Pengutronix e.K.                           | Uwe Kleine-K?nig            |
Industrial Linux Solutions                 | http://www.pengutronix.de/  |