linux-kernel - Re: [PATCH linux-next] iommu: Enable LPAE pagetable on ARM only

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Message-ID: <CAMuHMdXpSbEdrQ=1-m_MBv6RUb92waZ0BjLr1p790R9+L3Z8ww@mail.gmail.com>
Date:	Tue, 24 Feb 2015 11:33:02 +0100
From:	Geert Uytterhoeven <geert@...ux-m68k.org>
To:	Laurent Pinchart <laurent.pinchart@...asonboard.com>
Cc:	Vincent Stehlé <vincent.stehle@...oste.net>,
	iommu@...ts.linux-foundation.org,
	Linux-Next <linux-next@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	Will Deacon <will.deacon@....com>
Subject: Re: [PATCH linux-next] iommu: Enable LPAE pagetable on ARM only

On Mon, Feb 23, 2015 at 5:52 PM, Laurent Pinchart
<laurent.pinchart@...asonboard.com> wrote:
> On Sunday 22 February 2015 17:09:06 Vincent Stehlé wrote:
>> LPAE iommu page table makes sense only for ARM architecture. Add the
>> corresponding dependency in Kconfig.
>>
>> This fixes the following runtime warnings on PA-RISC architecture:
>
> I suppose this is caused by the selftest code ?
>
>>   WARNING: at drivers/iommu/io-pgtable-arm.c:413
>>   Modules linked in:
>>   CPU: 0 PID: 1 Comm: swapper/0 Not tainted
>> 3.19.0-next-20150222-00002-gc420256 #2 task: 17ca0000 ti: 17ca8000 task.ti:
>> 17ca8000
>>
>>        YZrvWESTHLNXBCVMcbcbcbcbOGFRQPDI
>>   PSW: 00000000000001001111111100001111 Not tainted
>>   r00-03  0004ff0f 0000001b 104871b0 17ca83c0
>>   r04-07  00001000 00000000 00000000 00000000
>>   r08-11  00000000 40001000 1013b36c 17ca8248
>>   r12-15  00000080 17e712c0 00000000 17c5e100
>>   r16-19  0000000c 105d8eb0 40001000 ffffffff
>>   r20-23  00000000 00800020 1048717c 00000000
>>   r24-27  00001000 00000000 00000009 10774ce0
>>   r28-31  00000000 00000027 17ca8480 10486d44
>>   sr00-03  00000000 00000000 00000000 00000000
>>   sr04-07  00000000 00000000 00000000 00000000
>>
>>   IASQ: 00000000 00000000 IAOQ: 10486df4 10486df8
>>    IIR: 03ffe01f    ISR: 00000000  IOR: 17c86e54
>>    CPU:        0   CR30: 17ca8000 CR31: 00000002
>>    ORIG_R28: 00000001
>>    IAOQ[0]: __arm_lpae_unmap+0x144/0x4cc
>>    IAOQ[1]: __arm_lpae_unmap+0x148/0x4cc
>>    RP(r2): arm_lpae_unmap+0x34/0x6c
>>   Backtrace:
>>    [<104871b0>] arm_lpae_unmap+0x34/0x6c
>>    [<10127944>] 0x10127944
>>    [<10168ee0>] do_one_initcall+0x128/0x1dc
>>    [<101028fc>] 0x101028fc
>>    [<10161b48>] kernel_init+0x1c/0x118
>>    [<1015d01c>] end_fault_vector+0x1c/0x24
>>    [<101762ec>] save_stack_trace+0x28/0x60
>>
>> Signed-off-by: Vincent Stehlé <vincent.stehle@...oste.net>
>> Cc: Laurent Pinchart <laurent.pinchart@...asonboard.com>
>> Cc: Will Deacon <will.deacon@....com>
>> ---
>>
>>
>> Hi,
>>
>> This can be seen with e.g. Linux next-20150222 on parisc with allmodconfig.
>>
>> Best regards,
>>
>> V.
>>
>>
>>  drivers/iommu/Kconfig | 1 +
>>  1 file changed, 1 insertion(+)
>>
>> diff --git a/drivers/iommu/Kconfig b/drivers/iommu/Kconfig
>> index baa0d97..c73fd72 100644
>> --- a/drivers/iommu/Kconfig
>> +++ b/drivers/iommu/Kconfig
>> @@ -22,6 +22,7 @@ config IOMMU_IO_PGTABLE
>>
>>  config IOMMU_IO_PGTABLE_LPAE
>>       bool "ARMv7/v8 Long Descriptor Format"
>> +     depends on ARM
>
> How about ARM || COMPILE_TEST ? It can still be useful to compile the module
> on other architectures.

COMPILE_TEST is meant for test-compiling drivers or subsystems that are not
useful on all platforms. IMHO COMPILE_TEST kernels are still supposed to boot
without ill effects.

Now, I understand the issue on PA-RISC is with the selftest, not with the actual
IOMMU_IO_PGTABLE_LPAE module? Then IOMMU_IO_PGTABLE_LPAE
can depend on ARM || COMPILE_TEST (|| ARM64, cfr. Laurent's later email).

But the selftest should protect itself against running on non-ARM, either
by making IOMMU_IO_PGTABLE_LPAE_SELFTEST depend on ARM(64)
(without "|| COMPILE_TEST"), or by adding a check to arm_lpae_do_selftests(),
to please all compile-testers.

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds
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