>
> [ Ingo, Venki and Shaohua added to cc: see the whole thread on lkml for
> details, but Mark is basically chasing down a situation where the floppy
> driver seems to have trouble formatting floppies, and it happened
> between 2.6.27 and .28. The trouble seems to be that a DMA transfer of a
> memory block transfers the wrong value for the first byte of the block.
>
> Which should be impossible, but whatever. Some part of the system has a
> cached buffer that isn't flushed.
>
> What gets _you_ guys involved is that Mark cannot reproduce the bug if
> HPET is disabled in the BIOS or by using 'nohpet'. He found that out by
> pure luck while bisecting, because some time during his bisect, his
> machine wouldn't even boot with HPET.
>
> So the problem is: with HPET enabled, 2.6.27.4 _used_ to work. But
> 2.6.28 (and current -git) does not. Any ideas? ]
>
> On Tue, 22 Dec 2009, Mark Hounschell wrote:
>>
>> Ok, I may have something that might help.
>>
>> # git bisect bad
>> 26afe5f2fbf06ea0765aaa316640c4dd472310c0 is the first bad commit
>> commit 26afe5f2fbf06ea0765aaa316640c4dd472310c0
>> Author:
venkatesh.pallipadi@intel.com <venkatesh.pallipadi@intel.com>
>> Date: Fri Sep 5 18:02:18 2008 -0700
>>
>> x86: HPET_MSI Initialise per-cpu HPET timers
>>
>> Initialize a per CPU HPET MSI timer when possible. We retain the HPET
>> timer 0 (IRQ 0) and timer 1 (IRQ 8) as is when legacy mode is being used. We
>> setup the remaining HPET timers as per CPU MSI based timers. This per CPU
>> timer will eliminate the need for timer broadcasting with IRQ 0 when there
>> is non-functional LAPIC timer across CPU deep C-states.
>>
>> If there are more CPUs than number of available timers, CPUs that do not
>> find any timer to use will continue using LAPIC and IRQ 0 broadcast.
>>
>> Signed-off-by: Venkatesh Pallipadi <venkatesh.pallipadi@intel.com>
>> Signed-off-by: Shaohua Li <shaohua.li@intel.com>
>> Signed-off-by: Ingo Molnar <mingo@elte.hu>
>>
>> And of coarse this was the first commit that I could not boot if I had hpet
>> enabled. To get this one to boot (single user mode only) I had to add the
>> the quiet cmdline option and following patch from to arch/x86/kernel/hpet.c
>>
>> commit 5ceb1a04187553e08c6ab60d30cee7c454ee139a
>>
>> @ -445,7 +445,7 @@ static int hpet_setup_irq(struct hpet_dev *dev)
>> {
>>
>> if (request_irq(dev->irq, hpet_interrupt_handler,
>> - IRQF_SHARED|IRQF_NOBALANCING, dev->name, dev))
>> + IRQF_DISABLED|IRQF_NOBALANCING, dev->name, dev))
>> return -1;
>>
>> disable_irq(dev->irq);
>>
>> AND add the quiet cmdline option.
>
> Ok, so we know why HPET didn't boot for you, and that was fixed later (by
> that 5ceb1a04). But is this also when the floppy started mis-behaving?
>
