linux-kernel - [patch] acpi throttling: fix endian bug in acpi_read_throttling

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Message-ID: <20120307115736.GB13204@elgon.mountain>
Date:	Wed, 7 Mar 2012 14:57:36 +0300
From:	Dan Carpenter <dan.carpenter@...cle.com>
To:	Len Brown <lenb@...nel.org>
Cc:	linux-acpi@...r.kernel.org, linux-kernel@...r.kernel.org,
	kernel-janitors@...r.kernel.org
Subject: [patch] acpi throttling: fix endian bug in
 acpi_read_throttling_status()

Using a u64 here creates an endian bug.  We store a u32 number in the
top byte which is a larger number than intended on big endian systems.
There is no reason to use a 64 bit data type here, I guess it was just
an oversight.

I removed the initialization to zero as well.  It's needed with a u64
but with a u32, the variable gets initialized properly inside the call
to acpi_os_read_port().

Signed-off-by: Dan Carpenter <dan.carpenter@...cle.com>

diff --git a/drivers/acpi/processor_throttling.c b/drivers/acpi/processor_throttling.c
index 605a295..1d02b7b 100644
--- a/drivers/acpi/processor_throttling.c
+++ b/drivers/acpi/processor_throttling.c
@@ -769,7 +769,7 @@ static int acpi_read_throttling_status(struct acpi_processor *pr,
 					u64 *value)
 {
 	u32 bit_width, bit_offset;
-	u64 ptc_value;
+	u32 ptc_value;
 	u64 ptc_mask;
 	struct acpi_processor_throttling *throttling;
 	int ret = -1;
@@ -777,12 +777,11 @@ static int acpi_read_throttling_status(struct acpi_processor *pr,
 	throttling = &pr->throttling;
 	switch (throttling->status_register.space_id) {
 	case ACPI_ADR_SPACE_SYSTEM_IO:
-		ptc_value = 0;
 		bit_width = throttling->status_register.bit_width;
 		bit_offset = throttling->status_register.bit_offset;
 
 		acpi_os_read_port((acpi_io_address) throttling->status_register.
-				  address, (u32 *) &ptc_value,
+				  address, &ptc_value,
 				  (u32) (bit_width + bit_offset));
 		ptc_mask = (1 << bit_width) - 1;
 		*value = (u64) ((ptc_value >> bit_offset) & ptc_mask);
--
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