linux-kernel - Re: [PATCH] agp/intel: Fix dma mask for Sandybridge

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Date:	Mon, 23 Aug 2010 14:48:54 +0800
From:	Zhenyu Wang <zhenyuw@...ux.intel.com>
To:	Takashi Iwai <tiwai@...e.de>
Cc:	Eric Anholt <eric@...olt.net>, David Airlie <airlied@...ux.ie>,
	dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] agp/intel: Fix dma mask for Sandybridge

On 2010.08.23 08:31:42 +0200, Takashi Iwai wrote:
> > bit 31			 bit 11			 bit 4			bit 0
> >    |<-physical addr 31:12->|<-physical addr 39:32->|<-cache ctl 3:1->|valid|
> 
> Then I really don't understand why it works.
> You shift 28bit and mask with 0xff.  Obviously it overwrite bits 0:3
> with original 28:31 bits.  Masking 0xff0 fixes the issue.
> 

ah, sorry, my stupid. Thanks for catching this!

Subject: [PATCH] agp/intel: fix physical address mask bits for sandybridge

It should shift bit 39-32 into pte's bit 11-4.

Reported-by: Takashi Iwai <tiwai@...e.de>
Signed-off-by: Zhenyu Wang <zhenyuw@...ux.intel.com>
---
 drivers/char/agp/intel-gtt.c |    4 ++--
 1 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/char/agp/intel-gtt.c b/drivers/char/agp/intel-gtt.c
index d22ffb8..0edfc87 100644
--- a/drivers/char/agp/intel-gtt.c
+++ b/drivers/char/agp/intel-gtt.c
@@ -1333,8 +1333,8 @@ static unsigned long intel_i965_mask_memory(struct agp_bridge_data *bridge,
 static unsigned long intel_gen6_mask_memory(struct agp_bridge_data *bridge,
 					    dma_addr_t addr, int type)
 {
-	/* Shift high bits down */
-	addr |= (addr >> 28) & 0xff;
+	/* gen6 has bit11-4 for physical addr bit39-32 */
+	addr |= (addr >> 28) & 0xff0;
 
 	/* Type checking must be done elsewhere */
 	return addr | bridge->driver->masks[type].mask;
-- 
1.7.0.4

-- 
Open Source Technology Center, Intel ltd.

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