Re: [PATCH][resending] SPARC32: forced setting of mode of SUN4M per-cpu timers

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Hi Kirill.

Glad to see that you are looking into timer stuff on sparc32!

On Thu, Jan 05, 2012 at 06:27:54AM +0400, Kirill Tkhai wrote:
> SPARC32: forced setting of mode of SUN4M per-cpu timers
The subject only belongsi n the subject: line of the mail - do
not repeat it in the mail body.

Patches that touch both sparc32 and sparc64 shall be prefixed:
sparc: bla bla

Patches that touches only sparc32 shall be prefixed:
sparc32: bla bla

So if you use lower-case sparc32 I am happy.


> SUN4M per-cpu timers have two modes of work. These are timer mode and counter mode.
> SPARC32 doesn't write anything to the register, which is connected with mode choice.
> So, the mode is chosen by bootloader. This patch forces to use timer mode from the
> kernel and to be independent of bootloader.
> 
> I had this problem with OpenBIOS. Timers didn't use to tick and kernel on QEMU used
> to fail, when it's compiled with SMP support. The patch fixes problem.

Good description!

> 
> Signed-off-by: Tkhai Kirill <tkhai@xxxxxxxxx>
> ---
> 
> diff --git a/arch/sparc/kernel/sun4m_irq.c b/arch/sparc/kernel/sun4m_irq.c
> index 422c16d..aa0b9df 100644
> --- a/arch/sparc/kernel/sun4m_irq.c
> +++ b/arch/sparc/kernel/sun4m_irq.c
> @@ -414,6 +414,10 @@ static void __init sun4m_init_timers(irq_handler_t counter_fn)
>  
>  	for (i = 0; i < num_cpu_timers; i++)
>  		sbus_writel(0, &timers_percpu[i]->l14_limit);
> +#ifdef CONFIG_SMP
> +	/* Timer-mode for every per-cpu timer (bit '0' is timer mode) */
> +	sbus_writel(0x00000000, &timers_global->timer_config);
> +#endif

Does this have to be SMP only - I think not.

It would also be nicer to move this up a few lines so it is
right before:

	sbus_writel((((1000000/HZ) + 1) << 10), &timers_global->l10_limit);

Then we have the config in one place.

I looked in the sun4m manual which says:

"
The value of the User Timer and Count and Limit registers is unspecified after the
corresponding configuration bit has been changed.
It is required for software to initialize the counter after a mode
change by writing to it in order to set the register value and to
clear the limit bit. When the counter is programmed to be
a User Timer the Counter/Timer function is disabled,
and vice–versa; these functions share one counter, so no state is
preserved across mode changes.
"

So we should actually set the config bit before we set the limit.

Your comment says:
> +	/* Timer-mode for every per-cpu timer (bit '0' is timer mode) */

But the sun4m manual specify that the first four bits correspond to each
of the per-cpu timers. So we actually need to set all four lower bits to 0.
Which you do - but the comment is wrong.

	Sam

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