linux-kernel - [PATCH] cciss: change Cmd_sg_list.sg_chain_dma type to dma_addr

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Date:	Tue, 17 Nov 2009 20:20:22 -0700
From:	Alex Chiang <achiang@...com>
To:	jens.axboe@...cle.com
Cc:	Don Brace <brace@...rdog.cce.hp.com>,
	"Stephen M. Cameron" <scameron@...rdog.cce.hp.com>,
	linux-kernel@...r.kernel.org
Subject: [PATCH] cciss: change Cmd_sg_list.sg_chain_dma type to dma_addr_t

A recent commit broke the ia64 build:

	Author: Don Brace <brace@...rdog.cce.hp.com>
	Date:   Thu Nov 12 12:50:01 2009 -0600

	cciss: Add enhanced scatter-gather support.

because of this hunk:

	--- a/drivers/block/cciss.h
	+++ b/drivers/block/cciss.h
	+struct Cmd_sg_list {
	+       SGDescriptor_struct     *sgchain;
	+       dma64_addr_t            sg_chain_dma;
	+       int                     chain_block_size;
	+};

The issue is that dma64_addr_t isn't #define'd on ia64.

The way that we're using Cmd_sg_list.sg_chain_dma is to hold an
address returned from pci_map_single().

	+               temp64.val = pci_map_single(h->pdev,
	+                                 h->cmd_sg_list[c->cmdindex]->sgchain,
	+                                 len, dir);
	+
	+               h->cmd_sg_list[c->cmdindex]->sg_chain_dma = temp64.val;

pci_map_single() returns a dma_addr_t too.

This code will still work even on a 32-bit x86 build, where
dma_addr_t is defined to be a u32 because it will simply be
promoted to the __u64 that temp64.val is defined as.

Thus, declaring Cmd_sg_list.sg_chain_dma as dma_addr_t is safe.

Cc: Don Brace <brace@...rdog.cce.hp.com>
Cc: Stephen M. Cameron <scameron@...rdog.cce.hp.com>
Signed-off-by: Alex Chiang <achiang@...com>
---
This changelog is probably an analysis overkill, but I was
concerned about 32 vs 64 bit DMA addresses getting passed to the
hardware. After doing a bunch more reading, I'm satisfied that a)
we're dealing with CPU-side addresses and b) proper type
promotion occurs anyway.

If anyone wants to double-check my work, I won't be offended. ;)

I build tested this on ia64, x86_64, and i386. No gcc nor sparse
warnings. However, I didn't do any run-time testing on i386.
---
diff --git a/drivers/block/cciss.h b/drivers/block/cciss.h
index e5c63e5..1d95db2 100644
--- a/drivers/block/cciss.h
+++ b/drivers/block/cciss.h
@@ -57,7 +57,7 @@ typedef struct _drive_info_struct
 
 struct Cmd_sg_list {
 	SGDescriptor_struct	*sgchain;
-	dma64_addr_t		sg_chain_dma;
+	dma_addr_t		sg_chain_dma;
 	int			chain_block_size;
 };
 
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