linux-kernel - Re: [PATCH] ALSA: hda-intel - Disable MSI support by default

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Date:	Wed, 15 Nov 2006 11:49:28 -0800
From:	Stephen Hemminger <shemminger@...l.org>
To:	Jeff Garzik <jeff@...zik.org>
Cc:	Linux Kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] ALSA: hda-intel - Disable MSI support by default

On Wed, 15 Nov 2006 14:23:20 -0500
Jeff Garzik <jeff@...zik.org> wrote:

> Stephen Hemminger wrote:
> > On Tue, 14 Nov 2006 23:24:04 -0500
> > Jeff Garzik <jeff@...zik.org> wrote:
> > 
> >> David Miller wrote:
> >>> Is this absolutely true?  I've never been sure about this point, and I
> >>> was rather convinced after reading various documents that once you
> >>> program up the MSI registers to start generating MSI this implicitly
> >>> disabled INTX and this was even in the PCI specification.
> >>>
> >>> It would be great to get a definitive answer on this.
> >>>
> >>> If it is mandatory, perhaps the driver shouldn't be doing it and
> >>> rather the PCI layer MSI enabling should.
> > 
> > pci_enable_msi() calls msi_capability_init() and that disables intx
> > already.
> [...]
> > The driver shouldn't deal with this, pci_disable_msi() does.
> 
> Explicit code reference please?
> 
> AFAICS the PCI layer only touched INTx bit for PCI-Express devices.

Yeah, why is that? Shouldn't it always be adjusting intx. 
Are there are any MSI capable devices on non-PCI express?
Sorry, don't have PCI spec (costs real $$) to check.

--- 2.6.19-rc5.orig/drivers/pci/msi.c	2006-11-15 11:46:23.000000000 -0800
+++ 2.6.19-rc5/drivers/pci/msi.c	2006-11-15 11:46:55.000000000 -0800
@@ -255,10 +255,7 @@
 		pci_write_config_word(dev, msi_control_reg(pos), control);
 		dev->msix_enabled = 1;
 	}
-    	if (pci_find_capability(dev, PCI_CAP_ID_EXP)) {
-		/* PCI Express Endpoint device detected */
-		pci_intx(dev, 0);  /* disable intx */
-	}
+	pci_intx(dev, 0);  /* disable intx */
 }
 
 void disable_msi_mode(struct pci_dev *dev, int pos, int type)
@@ -276,10 +273,8 @@
 		pci_write_config_word(dev, msi_control_reg(pos), control);
 		dev->msix_enabled = 0;
 	}
-    	if (pci_find_capability(dev, PCI_CAP_ID_EXP)) {
-		/* PCI Express Endpoint device detected */
-		pci_intx(dev, 1);  /* enable intx */
-	}
+
+	pci_intx(dev, 1);  /* re-enable intx */
 }
 
 static int msi_lookup_irq(struct pci_dev *dev, int type)

		


-- 
Stephen Hemminger <shemminger@...l.org>
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