Re: gm45 intel gfx can generate non-MSI irq# in MSI mode (was Re:[PATCH] drm/i915: stop using GMBUS IRQs on Gen4 chips (was Re: [3.9-rc1]irq 16: nobody cared (was [3.9-rc1] very poor interrupt responses

From: Jiri Kosina
Date: Wed Mar 20 2013 - 19:14:55 EST

On Tue, 19 Mar 2013, Yinghai Lu wrote:

> > I guess I should have phrased it more precisely, but that's exactly
> > what I expect is happening on my machine: I don't have anything on
> > irq16 (i.e. in non-msi mode the gfx interrupt isn't shared) and hence
> > the irq is completely disabled. Which obviously makes it impossible
> > for me to reproduce the issue. To test that theory, is there a quick
> > way to force-enable a given interrupt, short of just hacking up a 2nd
> > dummy irq handler in my driver?
> You may try to add another request_irq()
> after i915_load_modeset_init==>drm_irq_install.
> That could install one dummy action for ioapic irq for i915.
> Also you may need to add one quirk that does not disable intx during
> msi enabling like:
> 0x2e22,
> quirk_msi_intx_disable_bug);

This seemed to be really promising idea to me, as the DisINTx+ vs INTx+
discrepancy is very good hint, but unfortunately, after applying this:

drivers/pci/quirks.c | 3 +++
1 files changed, 3 insertions(+), 0 deletions(-)

diff --git a/drivers/pci/quirks.c b/drivers/pci/quirks.c
index 0369fb6..8508e24 100644
--- a/drivers/pci/quirks.c
+++ b/drivers/pci/quirks.c
+ quirk_msi_intx_disable_bug);
#endif /* CONFIG_PCI_MSI */

/* Allow manual resource allocation for PCI hotplug bridges

The problem is still there ... so the inconsistency between DisINTx+ and
INTx+ is unfortunately not the whole story.

Jiri Kosina
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