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ARM: PJ4: move coprocessor register access sequences to iwmmxt.S

Message ID CAKv+Gu8nyjEd7n=aWjMHa0Lziu9qy=gTvyBL4ckieQLcTo-H3w@mail.gmail.com
State New
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Commit Message

Ard Biesheuvel Dec. 17, 2015, 10:31 a.m. UTC
On 17 December 2015 at 11:27, Russell King - ARM Linux
<linux@arm.linux.org.uk> wrote:
> On Fri, Nov 13, 2015 at 08:23:34PM +0100, Ard Biesheuvel wrote:

>> On 13 November 2015 at 19:48, Stephen Boyd <sboyd@codeaurora.org> wrote:

>> > On 11/13, Ard Biesheuvel wrote:

>> >> The PJ4 inline asm sequences in pj4-cp0.c 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.

>> >>

>> >> So instead, revert to building pj4-cp0.c in Thumb-2 mode, and move the

>> >> offending sequence to iwmmxt.S, which is not instrumented anyway, and is

>> >> already built in ARM mode unconditionally.

>> >>

>> >> Reported-by: Stephen Boyd <sboyd@codeaurora.org>

>> >> Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>

>> >> ---

>> >

>> > Tested-by: Stephen Boyd <sboyd@codeaurora.org>

>> >

>>

>> Thanks.

>>

>> I've put this into the patch system (8452/1)

>

> And I've dropped it from my tree because it's broken.

>

> Come on guys, you can do better than this:

>

> arch/arm/kernel/built-in.o: In function `pj4_cp0_init':

> arch/arm/kernel/psci-call.o:(.init.text+0x22d0): undefined reference to `pj4_cp_access_write'

> arch/arm/kernel/psci-call.o:(.init.text+0x22e0): undefined reference to `pj4_cp_access_write'

> arch/arm/kernel/psci-call.o:(.init.text+0x2304): undefined reference to `pj4_cp_access_read'

> arch/arm/kernel/psci-call.o:(.init.text+0x2310): undefined reference to `pj4_cp_access_write'

> arch/arm/kernel/psci-call.o:(.init.text+0x2314): undefined reference to `pj4_cp_access_read'

>

> Let's look at the makefile:

>

> obj-$(CONFIG_CPU_PJ4)           += pj4-cp0.o

> obj-$(CONFIG_CPU_PJ4B)          += pj4-cp0.o

> obj-$(CONFIG_IWMMXT)            += iwmmxt.o

>

> Now, you're moving code from pj4-cp0.c to iwmmxt.S, and of course, you

> checked that IWMMXT would always be enabled if either PJ4 or PJ4B are

> enabled.

>

> config IWMMXT

>         bool "Enable iWMMXt support"

>         depends on CPU_XSCALE || CPU_XSC3 || CPU_MOHAWK || CPU_PJ4 || CPU_PJ4B

>         default y if PXA27x || PXA3xx || ARCH_MMP || CPU_PJ4 || CPU_PJ4B

>

> Err, no, IWMMXT can be disabled.  Hence the build errors.

>

> Please, take more time when moving code around to ensure that this kind

> of build breakage doesn't creep in.  It's *really* easy to check, it

> only takes a couple of additional minutes.

>


Yes, I was just looking into it after Arnd mentioned it over IRC

If you can live with not having the pr_info() that warns you when
running on a PJ4 with iWMMXt while CONFIG_IWMMXT is disabled, I could
just drop pj4-cp0.c from the build entirely, i.e.,

http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
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Patch

diff --git a/arch/arm/kernel/Makefile b/arch/arm/kernel/Makefile
index af9e59bf3831..9d798fb17359 100644
--- a/arch/arm/kernel/Makefile
+++ b/arch/arm/kernel/Makefile
@@ -67,13 +67,12 @@  obj-$(CONFIG_HAVE_HW_BREAKPOINT)    += hw_breakpoint.o
 obj-$(CONFIG_CPU_XSCALE)       += xscale-cp0.o
 obj-$(CONFIG_CPU_XSC3)         += xscale-cp0.o
 obj-$(CONFIG_CPU_MOHAWK)       += xscale-cp0.o
-obj-$(CONFIG_CPU_PJ4)          += pj4-cp0.o
-obj-$(CONFIG_CPU_PJ4B)         += pj4-cp0.o
-obj-$(CONFIG_IWMMXT)           += iwmmxt.o
+iwmmxt-obj-$(CONFIG_CPU_PJ4)   := pj4-cp0.o
+iwmmxt-obj-$(CONFIG_CPU_PJ4B)  := pj4-cp0.o
+obj-$(CONFIG_IWMMXT)           += iwmmxt.o $(iwmmxt-obj-y)
 obj-$(CONFIG_PERF_EVENTS)      += perf_regs.o perf_callchain.o
 obj-$(CONFIG_HW_PERF_EVENTS)   += perf_event_xscale.o perf_event_v6.o \
                                   perf_event_v7.o

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