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SubjectRe: [PATCH] HPET: Workaround for a BIOS workaround on AMD SB700 platform
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Hi Thomas,

Your modification has been checked OK on our SB700 platform. Thank you.
Now could you help us to merge your patch to kernel source? Or do I need
to resubmit a patch on it?

Best regards,
- Crane

On Thu, 2008-08-14 at 18:11 +0800, Thomas Gleixner wrote:

> Crane,
>
> thanks for debugging this. I think we don't need a quirk for this
> workaround. Checking the config register value for 0xffffffff is safe
> on all machines. I simplified your patch to the one below and added a
> printk in case the check times out.
>
> One thing I'm a bit wary about is the readout of the HPET_PERIOD
> register. Is the value correct even _before_ the SMM machinery is
> started ?

> Thanks,
>
> tglx
> -----
> diff --git a/arch/x86/kernel/hpet.c b/arch/x86/kernel/hpet.c
> index ad2b15a..59fd3b6 100644
> --- a/arch/x86/kernel/hpet.c
> +++ b/arch/x86/kernel/hpet.c
> @@ -359,6 +359,7 @@ static int hpet_clocksource_register(void)
> int __init hpet_enable(void)
> {
> unsigned long id;
> + int i;
>
> if (!is_hpet_capable())
> return 0;
> @@ -369,6 +370,29 @@ int __init hpet_enable(void)
> * Read the period and check for a sane value:
> */
> hpet_period = hpet_readl(HPET_PERIOD);
> +
> + /*
> + * AMD SB700 based systems with spread spectrum enabled use a
> + * SMM based HPET emulation to provide proper frequency
> + * setting. The SMM code is initialized with the first HPET
> + * register access and takes some time to complete. During
> + * this time the config register reads 0xffffffff. We check
> + * for max. 1000 loops whether the config register reads a non
> + * 0xffffffff value to make sure that HPET is up and running
> + * before we go further. A counting loop is safe, as the HPET
> + * access takes thousands of CPU cycles. On non SB700 based
> + * machines this check is only done once and has no side
> + * effects.
> + */
> + for (i = 0; hpet_readl(HPET_CFG) == 0xFFFFFFFF; i++) {
> + if (i == 1000) {
> + printk(KERN_WARNING
> + "HPET config register value = 0xFFFFFFFF. "
> + "Disabling HPET\n");
> + goto out_nohpet;
> + }
> + }
> +
> if (hpet_period < HPET_MIN_PERIOD || hpet_period > HPET_MAX_PERIOD)
> goto out_nohpet;
>




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