Re: [PATCH] [stable 3.18 through 4.4] ARM: 8452/3: PJ4: make coprocessor access sequences buildable in Thumb2 mode

[gregkh <gregkh@linuxfoundation.org>]

On Mon, May 08, 2017 at 09:57:54PM +0200, Arnd Bergmann wrote:
> On Mon, May 8, 2017 at 9:55 PM, Arnd Bergmann <arnd@arndb.de> wrote:
> > From: Ard Biesheuvel <ard.biesheuvel@linaro.org>
> >
> > Commit 5008efc83bf85b647aa1cbc44718b1675bbb7444 upstream.
> >
> > The PJ4 inline asm sequence to write to cp15 cannot be built in Thumb-2
> > mode, due to the way it performs arithmetic on the program counter, so it
> > is built in ARM mode instead. However, building C files in ARM mode under
> > CONFIG_THUMB2_KERNEL is problematic, since the instrumentation performed
> > by subsystems like ftrace does not expect having to deal with interworking
> > branches.
> >
> > Since the sequence in question is simply a poor man's ISB instruction,
> > let's use a straight 'isb' instead when building in Thumb2 mode. Thumb2
> > implies V7, so 'isb' should always be supported in that case.
> >
> > Acked-by: Arnd Bergmann <arnd@arndb.de>
> > Acked-by: Nicolas Pitre <nico@linaro.org>
> > Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
> > Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
> > Signed-off-by: Arnd Bergmann <arnd@arndb.de>
> > ---
> > Hi Greg,
> >
> > As Ard pointed out, commit 13d1b9575ac2c2da ("ARM: 8221/1: PJ4: allow
> > building in Thumb-2 mode") which I suggested for backports into
> > 3.16 is broken unless we also take this one.
> >
> > I checked the other stable branches and found that both 3.18 and
> > 4.4 contain only the first of the two, so please apply this one on
> > both branches as well.
> 
> Clarification: please apply this patch from email on 3.18.y and
> cherry-pick the original 5008efc83bf85b6 on 4.4.y to avoid
> rebasing yourself.

Now queued up this way, thanks.

greg k-h