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[PATCH 1/2] [PCI] Check that MWI bit really did get set

From:  Matthew Wilcox <matthew-AT-wil.cx>
To:  Val Henson <val_henson-AT-linux.intel.com>, Greg Kroah-Hartman <gregkh-AT-suse.de>
Subject:  [PATCH 1/2] [PCI] Check that MWI bit really did get set
Date:  Fri, 06 Oct 2006 13:05:18 -0600
Cc:  netdev-AT-vger.kernel.org, linux-pci-AT-atrey.karlin.mff.cuni.cz, linux-kernel-AT-vger.kernel.org, Matthew Wilcox <matthew-AT-wil.cx>
Archive-link:  Article, Thread

Since some devices may not implement the MWI bit, we should check that
the write did set it and return an error if it didn't.

Signed-off-by: Matthew Wilcox <matthew@wil.cx>

diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
index a544997..3d041f4 100644
--- a/drivers/pci/pci.c
+++ b/drivers/pci/pci.c
@@ -900,13 +900,17 @@ #endif
 		return rc;
 
 	pci_read_config_word(dev, PCI_COMMAND, &cmd);
-	if (! (cmd & PCI_COMMAND_INVALIDATE)) {
-		pr_debug("PCI: Enabling Mem-Wr-Inval for device %s\n", pci_name(dev));
-		cmd |= PCI_COMMAND_INVALIDATE;
-		pci_write_config_word(dev, PCI_COMMAND, cmd);
-	}
-	
-	return 0;
+	if (cmd & PCI_COMMAND_INVALIDATE)
+		return 0;
+
+	pr_debug("PCI: Enabling Mem-Wr-Inval for device %s\n", pci_name(dev));
+	cmd |= PCI_COMMAND_INVALIDATE;
+	pci_write_config_word(dev, PCI_COMMAND, cmd);
+
+	/* read result from hardware (in case bit refused to enable) */
+	pci_read_config_word(dev, PCI_COMMAND, &cmd);
+
+	return (cmd & PCI_COMMAND_INVALIDATE) ? 0 : -EINVAL;
 }
 
 /**
-
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