Re: [PATCH] pci: Add a few new IDs for Intel GPU "spurious interrupt" quirk

[Bin Meng]

Hi David,

On Mon, Oct 8, 2018 at 6:06 PM David Laight <David.Laight@xxxxxxxxxx> wrote:
>
> From: Bin Meng
> > Sent: 08 October 2018 10:44
> ...
> > Correct, disable the shared interrupt line keeps all devices using
> > that line from working, which is current kernel's behavior w/o this
> > quirk handling: it disables the (shared) interrupt line after 100.000+
> > generated interrupts. But the side effect is that other devices become
> > unusable after that (eg: USB devices which share the same interrupt
> > line with the Intel GPU). That's why the original commit, f67fd55fa96f
> > ("PCI: Add quirk for still enabled interrupts on Intel Sandy Bridge
> > GPUs") disables the GPU's interrupt directly, which should really be
> > done by the VGA BIOS itself (a buggy VBIOS!).
>
> Shouldn't the kernel just disable all PCI(e) interrupts by writing
> 1 to the config space control register bit during grope?
> Can it ever by right for this to be set?
>

Do you mean PCI_COMMAND_INTX_DISABLE bit of the command register in
the configuration space? Setting this bit indeed could disable the
INTx interrupt, but it does not work for all PCI devices as this bit
was introduced in PCI spec v2.3.

> Apart from VGA the 'bus master' bit also needs to be clear.
>
> ISTR some very early PCI systems which failed to reset the PCI
> bus during reboot - at least the 'bus master' bit remained
> set for an ethernet card.
> On a private LAN the OS got reinstalled and rebooted without
> using all the ethernet receive buffers and then died because
> a receive frame got written into 'random' memory.

Regards,
Bin