Re: [PATCHv2 2/3] ARM: Detect support for SDIV/UDIV from ISAR0 register

Uwe Kleine-König
2013-04-18T09:10:26Z

Hello Stephen,

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@arm.com>
> Cc: Stepan Moskovchenko <stepanm@codeaurora.org>
> Signed-off-by: Stephen Boyd <sboyd@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;

?

Best regards
Uwe

--
Pengutronix e.K. | Uwe Kleine-König |
Industrial Linux Solutions | http://www.pengutronix.de/ |