[LinuxBIOS] [v2][PATCH] PCI PERR# and SERR#

[Marc Jones]

I found this problem on the AMD Geode db800 platform but it probably 
affects other platforms and chipsets. LinuxBIOS sets every PCI device 
PERR# enable and SERR# enable in the PCI Command Register. This is 
probably not the right thing to do for a number of reasons.

The PCI spec is not clear on what should be done with a PERR# it is a 
device, chipset and platform design desicsion and we don't know what the 
platform or device will do. For example, PERR# can be connected to SERR# 
which can be connected to reset. Instead of just getting a parity error 
you have now reset the system, oops.

Also, PERR# is required to be reported to system software. This has to 
be done through the driver via an interrupt (or through polling, ewwww). 
As you can see, a lot of pieces need to be in place, the device has to 
do the interrupt, the driver should do something with the PERR#, and 
then? I don't know if the kernel does anything with the PERR# message. 
LinuxBIOS is no longer in play so it can't do anything with the errors.

Because of the uncertainty of PERR# and SERR# I don't think that many 
manufacturers use it, especially in the consumer space. They may still 
detect and fix parity errors at the hardware level or in their driver, 
just not use the PERR# and SERR signals. Note that is a device does have 
a parity error it will still report it in

As I noted above, the SERR# can cause a system reset. I think that it 
would be better to do nothing and maybe the device will stop/hang/etc 
rather than to mysteriously reset. Again, let the system software decide 
policy.

All this seems like a good reason to let the driver and/or system level 
software enable PERR# and SERR# and for LinuxBIOS to leave them alone.

Dissenting opinions welcome.

Marc

[ron minnich]

On 9/25/07, Marc Jones  wrote:
> All this seems like a good reason to let the driver and/or system level
> software enable PERR# and SERR# and for LinuxBIOS to leave them alone.

you're right. I don't even remember when those started getting set,
and had not noticed it, but it's a mistake.

I'm almost inclined to say "leave that line in there commented out,
with a warning: NEVER DO THIS!". That's up to you.

Acked-by: Ronald G. Minnich

Quoting ron minnich :
> On 9/25/07, Marc Jones  wrote:
> > All this seems like a good reason to let the driver and/or system level
> > software enable PERR# and SERR# and for LinuxBIOS to leave them alone.
>
> you're right. I don't even remember when those started getting set,
> and had not noticed it, but it's a mistake.
>
> I'm almost inclined to say "leave that line in there commented out,
> with a warning: NEVER DO THIS!". That's up to you.
>
> Acked-by: Ronald G. Minnich

Marc, your the man! This is the exact problem I am having with the  
Intel 82801DB. When the PCI Bridge goes to "Enabling resources..." it  
just freezes. I have traced it back to the 	"command |=  
(PCI_COMMAND_PARITY + PCI_COMMAND_SERR); /* error check */" line. Yeh  
I have done alot of reading about parity errors and it seems to be  
something software drivers on the OS level use, not at the bios level.  
Parity error checking also seems to be very old method. So, I was  
starting to question why this line was even there. These bits are not  
set with the factory bios. Also, what about the  
pci_bus_enable_resources() function in pci_device.c? Do we want to  
comment out the "ctrl |= (PCI_BRIDGE_CTL_PARITY +  
PCI_BRIDGE_CTL_SERR); /* error check */" line also?? Anyways nice work  
Marc:-)

Acked-by: Joseph Smith

Thanks - Joe

[Marc Jones]

ron minnich wrote:
> On 9/25/07, Marc Jones  wrote:
> > All this seems like a good reason to let the driver and/or system level
> > software enable PERR# and SERR# and for LinuxBIOS to leave them alone.
>
> you're right. I don't even remember when those started getting set,
> and had not noticed it, but it's a mistake.
>
> I'm almost inclined to say "leave that line in there commented out,
> with a warning: NEVER DO THIS!". That's up to you.
>
> Acked-by: Ronald G. Minnich

I don't think that the warning is necessary. I prefer to just remove the 
code.
r2810

thanks,
Marc

[LinuxBIOS] [v2][PATCH] PCI PERR# and SERR# i82801xx

Thee lines in i82801xx_pci.c need to be removed. They cause the  
i82801DB to reset. See this thread for more info:

http://article.gmane.org/gmane.linux.bios/26791

Signed-off-by: Joseph Smith

Thanks - Joe

[LinuxBIOS] [v2][PATCH] PCI PERR# and SERR# i82801xx

[Corey Osgood]

[e-mail] wrote:
> Thee lines in i82801xx_pci.c need to be removed. They cause the
> i82801DB to reset. See this thread for more info:
>
> http://article.gmane.org/gmane.linux.bios/26791
>
> Signed-off-by: Joseph Smith
>
> Thanks - Joe

Acked-by: Corey Osgood

[LinuxBIOS] [v2][PATCH] PCI PERR# and SERR# i82801xx

[ron minnich]

Committed revision 2816.

ron