linux-kernel - [PATCH RFC] x86: Fix 64-bit DMA masks on VIA

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Date:	Wed, 23 Apr 2008 20:55:12 +0200
From:	Michael Buesch <mb@...sch.de>
To:	"linux-kernel" <linux-kernel@...r.kernel.org>
Cc:	vojtech@...e.cz, muli@...ibm.com, jdmason@...zu.us,
	tglx@...utronix.de, mingo@...hat.com
Subject: [PATCH RFC] x86: Fix 64-bit DMA masks on VIA

This untested patch is supposed to fix DMAing on some VIA boards.
Currently the DMA subsystem returns an error, if the driver does
tell that it supports a 64bit DMA mask. So the driver probing
would fail in that case. This happens for some b43 cards with
64bit DMA engines on VIA boards.
Instead of failing the dma_supported() check, simply strip off the
high 32bits.

Signed-off-by: Michael Buesch <mb@...sch.de>

---

This is not tested, due to the lack of hardware.


Index: wireless-testing/arch/x86/kernel/pci-dma_64.c
===================================================================
--- wireless-testing.orig/arch/x86/kernel/pci-dma_64.c	2008-04-01 15:53:17.000000000 +0200
+++ wireless-testing/arch/x86/kernel/pci-dma_64.c	2008-04-23 20:49:42.000000000 +0200
@@ -173,11 +173,8 @@ int dma_supported(struct device *dev, u6
 {
 #ifdef CONFIG_PCI
 	if (mask > 0xffffffff && forbid_dac > 0) {
-
-
-
 		printk(KERN_INFO "PCI: Disallowing DAC for device %s\n", dev->bus_id);
-		return 0;
+		/* We strip off the high 32 bits in dma_set_mask() */
 	}
 #endif
 
@@ -215,6 +212,10 @@ int dma_set_mask(struct device *dev, u64
 {
 	if (!dev->dma_mask || !dma_supported(dev, mask))
 		return -EIO;
+
+	if (forbid_dac > 0)
+		mask &= 0xffffffff;
+
 	*dev->dma_mask = mask;
 	return 0;
 }
Index: wireless-testing/include/asm-x86/dma-mapping_32.h
===================================================================
--- wireless-testing.orig/include/asm-x86/dma-mapping_32.h	2008-02-16 19:08:15.000000000 +0100
+++ wireless-testing/include/asm-x86/dma-mapping_32.h	2008-04-23 20:46:12.000000000 +0200
@@ -137,10 +137,6 @@ dma_supported(struct device *dev, u64 ma
         if(mask < 0x00ffffff)
                 return 0;
 
-	/* Work around chipset bugs */
-	if (forbid_dac > 0 && mask > 0xffffffffULL)
-		return 0;
-
 	return 1;
 }
 
@@ -150,6 +146,10 @@ dma_set_mask(struct device *dev, u64 mas
 	if(!dev->dma_mask || !dma_supported(dev, mask))
 		return -EIO;
 
+	/* Work around chipset bugs */
+	if (forbid_dac > 0)
+		mask &= 0xffffffffULL;
+
 	*dev->dma_mask = mask;
 
 	return 0;

-- 
Greetings Michael.
--
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