[RFC PATCH] implement read_cpuid_ext for v7-M (Was: Re: [PATCHv2 2/3] ARM: Detect support for SDIV/UDIV from ISAR0) register

[Stephen Boyd]

On 05/06/13 02:30, Uwe Kleine-König wrote:
> Hello,
>
> On Thu, Apr 18, 2013 at 11:10:19AM +0200, Uwe Kleine-König wrote:
>> On Mon, Mar 18, 2013 at 11:28:56AM -0700, Stephen Boyd wrote:
>>> The ISAR0 register indicates support for the SDIV and UDIV
>>> instructions in both the Thumb and ARM instruction set. Read the
>>> register to detect the supported instructions and update the
>>> elf_hwcap mask as appropriate. This is better than adding more
>>> and more cpuid checks in proc-v7.S for each new cpu variant that
>>> supports these instructions.
>> you pointed out yesterday that this could work on v7-m, too. As I based
>> my patches on 3.9-rc1 this patch (8164f7af88) wasn't included. When
>> updating this results in a warning, because I have
>>
>> 	6ebd4d0 (ARM: stub out read_cpuid and read_cpuid_ext for CPU_CP15=n)
>>
>> from rmk's devel-stable branch.
>>  
>>> Acked-by: Will Deacon <will.deacon at arm.com>
>>> Cc: Stepan Moskovchenko <stepanm at codeaurora.org>
>>> Signed-off-by: Stephen Boyd <sboyd at codeaurora.org>
>>> ---
>>>  arch/arm/kernel/setup.c | 20 ++++++++++++++++++++
>>>  arch/arm/mm/proc-v7.S   |  4 ++--
>>>  2 files changed, 22 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/arch/arm/kernel/setup.c b/arch/arm/kernel/setup.c
>>> index e2c8bbf..f3ac13f 100644
>>> --- a/arch/arm/kernel/setup.c
>>> +++ b/arch/arm/kernel/setup.c
>>> @@ -353,6 +353,23 @@ void __init early_print(const char *str, ...)
>>>  	printk("%s", buf);
>>>  }
>>>  
>>> +static void __init cpuid_init_hwcaps(void)
>>> +{
>>> +	unsigned int divide_instrs;
>>> +
>>> +	if (cpu_architecture() < CPU_ARCH_ARMv7)
>>> +		return;
>>> +
>>> +	divide_instrs = (read_cpuid_ext(CPUID_EXT_ISAR0) & 0x0f000000) >> 24;
>> The problem is that read_cpuid_ext is called which doesn't map to
>> something useful for v7-m. So maybe add a check:
>>
>> 	if (!IS_ENABLED(CONFIG_CPU_CP15))
>> 		return;
>>
>> ?
> The patch below fixes the issue for me on V7-M. The only drawback is
> that the list of registers isn't shared. Maybe someone has a nice idea?

The patch looks ok to me.

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