Date:	Sat, 21 Feb 2009 13:06:39 -0600
From:	Robert Hancock <hancockrwd@...il.com>
To:	"Mr. Berkley Shands" <bshands@...gy.com>
CC:	linux-kernel <linux-kernel@...r.kernel.org>,
	linux-pci <linux-pci@...ey.karlin.mff.cuni.cz>
Subject: Re: AMD 8132 parity issue causes interrupt storms

Mr. Berkley Shands wrote:
> I am certainly not doing that :-)
> Some supermicro H8QME-2 motherboards (about 40%) show up with that enabled.
> Something generates a parity error, and the machine is instantly on its 
> knees until it gets power cycled.
> 
> My thought was to look and report that parity was being enabled (bios bug?)

That would be a BIOS bug then, if it sets the parity interrupts enabled 
by default. If the OS installs a driver to handle those interrupts, the 
driver can enable them, otherwise they should stay off.

We could probably create a PCI quirk for this chip that would disable 
the parity interrupts on bootup if it found them enabled.. CCing linux-pci.

> 
> I can fix it in a number of ways with setpci. It has taken a year to 
> find the cause of my troubles.
> And a $15K scope, ...
> 
> Berkley
> 
> 
> Robert Hancock wrote:
>> Mr. Berkley Shands wrote:
>>> It seems that the 8132 should be blacklisted :-)
>>>
>>> INT-A will be asserted forever if any channel sees a parity error.
>>> This can be blocked by several means;
>>>
>>> 1) setpci -s <bus address of 8132> 5.b=05   /* disable interrupts 
>>> from the bridge */
>>> This is the I don't see you method.
>>>
>>> Shouldn't the interrupt handler (is there one?) trap and clear this?
>>> Shouldn't the kernel at least report this error and reset those bits?
>>
>> What's enabling this interrupt generation? Interrupting on parity 
>> errors is not part of the PCI spec. Unless there's some driver that's 
>> set up to handle these interrupts, whoever's enabling them shouldn't be..
>>
>>>
>>> All,
>>>
>>> OK, here's what I know so far.  The interrupt storm is coming from 
>>> the parity error detector in the 8132.  The parity error is reported 
>>> in two locations using sticky bits:
>>>
>>> 0x1c bits 31 and 24
>>>   Here there seems to be some differentiation between which party 
>>> detected the parity error.  The 8132 spec is pretty vague here (see 
>>> page 75) but it looks like the 8132 is detecting a parity error from 
>>> the HBA not the other way around.
>>> 0x80 bit 0
>>>   Here it just states that someone asserted the PERR_L signal, no 
>>> distinction on who did it.
>>>
>>> All these bits are write-one-to-clear.  If 0x80 bit 0 is cleared, the 
>>> storm stops.  Clearly the OS does not know how to handle these 
>>> conditions and the error flag is left on while the interrupt is 
>>> continuously handled.
>>>
>>> One way to handle this is to set 0x48 bit 19 to 0.  This prevents the 
>>> 8132 from interrupting when 0x80 bit 0 is set.
>>>
>>> A much better way to handle this is to have the interrupt handler 
>>> actually check the error bits on the 8132 when it is called.  This 
>>> would slow down the interrupt handler, but actually give us a much 
>>> better visibility into this problem (when, where and how often this 
>>> happens).  The irritating thing here is that this is chipset 
>>> dependent.  The interrupt handler would have to know what PCI-X 
>>> chipset it was talking through to know how to handle this (way to go 
>>> AMD).
>>>
>>> The really odd thing is that the parity error is reported through 
>>> INTB on the 8132.  The spec claims that fatal errors (the category 
>>> they put PERR in) go to INTB while hot plug conditions trigger INTA.  
>>> Masking off fatal errors in the IOAPIC turns off the storm too.  I 
>>> have no idea why this is showing up on INTA.
>>>
>>> Berkley
>>>
>>
>>
> 
> 
> -- 
> 
> // E. F. Berkley Shands, MSc//
> 
> ** Exegy Inc.**
> 
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> 

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