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

From: [email-masked] (Jonathan Austin)
Date: Tue, 07 May 2013 11:30:50 +0100

On 06/05/13 10:30, Uwe Kleine-K?nig wrote:
> Hello,
>
> On Thu, Apr 18, 2013 at 11:10:19AM +0200, Uwe Kleine-K?nig 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 <[email-masked]>
>>> Cc: Stepan Moskovchenko <[email-masked]>
>>> Signed-off-by: Stephen Boyd <[email-masked]>
>>> ---
>>>   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?

I looked at whether there was anything nice that we could do around this 
but it most things end up more ugly than a separate long list of 
defines... It also makes things hard to understand so I prefer having 
these extra defines.

On the other hand, I think that this is about the time to think about 
another file for V7M CPUID stuff...

This file is beginning to look a bit unruly with all the different cases 
(V7M, !CPU_CP15, as well as the functions like read_cpuid_part_number 
that have the same definition in all cases). Thoughts?

>
> BTW, there doesn't seem to be an equivalent register set for
> CPUID_{CACHETYPE,TCM,TLBTYPE,MPIDR} on v7-M.
>
> Best regards
> Uwe
>
> diff --git a/arch/arm/include/asm/cputype.h b/arch/arm/include/asm/cputype.h
> index 4eb94a3..ec635ff 100644
> --- a/arch/arm/include/asm/cputype.h
> +++ b/arch/arm/include/asm/cputype.h
> @@ -10,6 +10,22 @@
>   #define CPUID_TLBTYPE	3
>   #define CPUID_MPIDR	5
>
> +#ifdef CONFIG_CPU_V7M

Why not stick the

#include <asm/io.h>
#include <asm/v7m.h>

here?
> +#define CPUID_EXT_PFR0	0x40
> +#define CPUID_EXT_PFR1	0x44
> +#define CPUID_EXT_DFR0	0x48
> +#define CPUID_EXT_AFR0	0x4c
> +#define CPUID_EXT_MMFR0	0x50
> +#define CPUID_EXT_MMFR1	0x54
> +#define CPUID_EXT_MMFR2	0x58
> +#define CPUID_EXT_MMFR3	0x5c
> +#define CPUID_EXT_ISAR0	0x60
> +#define CPUID_EXT_ISAR1	0x64
> +#define CPUID_EXT_ISAR2	0x68
> +#define CPUID_EXT_ISAR3	0x6c
> +#define CPUID_EXT_ISAR4	0x70
> +#define CPUID_EXT_ISAR5	0x74
> +#else
>   #define CPUID_EXT_PFR0	"c1, 0"
>   #define CPUID_EXT_PFR1	"c1, 1"
>   #define CPUID_EXT_DFR0	"c1, 2"
> @@ -24,6 +40,7 @@
>   #define CPUID_EXT_ISAR3	"c2, 3"
>   #define CPUID_EXT_ISAR4	"c2, 4"
>   #define CPUID_EXT_ISAR5	"c2, 5"
> +#endif
>
>   #define MPIDR_SMP_BITMASK (0x3 << 30)
>   #define MPIDR_SMP_VALUE (0x2 << 30)
> @@ -79,7 +96,23 @@ extern unsigned int processor_id;
>   		__val;							\
>   	})
>
> -#else /* ifdef CONFIG_CPU_CP15 */
> +#elif defined(CONFIG_CPU_V7M)
> +
> +#include <asm/io.h>
> +#include <asm/v7m.h>
> +
> +#define read_cpuid(reg)							\
> +	({								\
> +		WARN_ON_ONCE(1);					\
> +		0;							\
> +	})
> +
> +static inline unsigned int __attribute_const__ read_cpuid_ext(unsigned offset)
> +{
> +	return readl(BASEADDR_V7M_SCB + offset);
> +}
> +
> +#else /* ifdef CONFIG_CPU_CP15 / elif defined (CONFIG_CPU_V7M) */
>
>   /*
>    * read_cpuid and read_cpuid_ext should only ever be called on machines that
> @@ -108,9 +141,6 @@ static inline unsigned int __attribute_const__ read_cpuid_id(void)
>
>   #elif defined(CONFIG_CPU_V7M)
>
> -#include <asm/io.h>
> -#include <asm/v7m.h>
> -
>   static inline unsigned int __attribute_const__ read_cpuid_id(void)
>   {
>   	return readl(BASEADDR_V7M_SCB + V7M_SCB_CPUID);
> diff --git a/arch/arm/mm/proc-v7m.S b/arch/arm/mm/proc-v7m.S
> index 000499c..0c93588 100644
> --- a/arch/arm/mm/proc-v7m.S
> +++ b/arch/arm/mm/proc-v7m.S
> @@ -144,7 +144,7 @@ __v7m_proc_info:
>   	b	__v7m_setup		@ proc_info_list.__cpu_flush
>   	.long	cpu_arch_name
>   	.long	cpu_elf_name
> -	.long	HWCAP_HALF|HWCAP_THUMB|HWCAP_FAST_MULT|HWCAP_IDIVT
> +	.long	HWCAP_HALF|HWCAP_THUMB|HWCAP_FAST_MULT
>   	.long	cpu_v7m_name
>   	.long	v7m_processor_functions	@ proc_info_list.proc
>   	.long	0			@ proc_info_list.tlb
>