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SubjectRE: [PATCH] acpi-cpufreq: Remove P-state read after a P-state write in normal path
Date
From
applied to acpi test tree.

thanks,
-Len

>-----Original Message-----
>From: Venkatesh Pallipadi [mailto:venkatesh.pallipadi@intel.com]
>Sent: Friday, August 26, 2005 8:11 PM
>To: Andrew Morton
>Cc: linux-kernel; Brown, Len
>Subject: [PATCH] acpi-cpufreq: Remove P-state read after a
>P-state write in normal path
>
>
>
>Remove P-state read status after a P-state write in normal case. As
>that operation is expensive. There are no known failures of a
>set and we can
>assume success in the common case. acpi_pstate_strict
>parameter can be used
>to force it back on any systems that is known to have errors.
>
>Signed-off-by: Venkatesh Pallipadi <venkatesh.pallipadi@intel.com>
>
>Index: linux-2.6.12/arch/i386/kernel/cpu/cpufreq/acpi-cpufreq.c
>===================================================================
>---
>linux-2.6.12.orig/arch/i386/kernel/cpu/cpufreq/acpi-cpufreq.c
>2005-08-16 09:41:52.977456128 -0700
>+++ linux-2.6.12/arch/i386/kernel/cpu/cpufreq/acpi-cpufreq.c
>2005-08-17 13:32:33.034651136 -0700
>@@ -31,6 +31,7 @@
> #include <linux/cpufreq.h>
> #include <linux/proc_fs.h>
> #include <linux/seq_file.h>
>+#include <linux/compiler.h>
> #include <asm/io.h>
> #include <asm/delay.h>
> #include <asm/uaccess.h>
>@@ -57,6 +58,8 @@
>
> static struct cpufreq_driver acpi_cpufreq_driver;
>
>+static unsigned int acpi_pstate_strict;
>+
> static int
> acpi_processor_write_port(
> u16 port,
>@@ -163,34 +166,44 @@
> }
>
> /*
>- * Then we read the 'status_register' and compare the
>value with the
>- * target state's 'status' to make sure the transition
>was successful.
>- * Note that we'll poll for up to 1ms (100 cycles of
>10us) before
>- * giving up.
>+ * Assume the write went through when
>acpi_pstate_strict is not used.
>+ * As read status_register is an expensive operation and there
>+ * are no specific error cases where an IO port write will fail.
> */
>-
>- port = data->acpi_data.status_register.address;
>- bit_width = data->acpi_data.status_register.bit_width;
>-
>- dprintk("Looking for 0x%08x from port 0x%04x\n",
>- (u32) data->acpi_data.states[state].status, port);
>-
>- for (i=0; i<100; i++) {
>- ret = acpi_processor_read_port(port, bit_width, &value);
>- if (ret) {
>- dprintk("Invalid port width 0x%04x\n",
>bit_width);
>- retval = ret;
>- goto migrate_end;
>+ if (acpi_pstate_strict) {
>+ /* Then we read the 'status_register' and
>compare the value
>+ * with the target state's 'status' to make sure the
>+ * transition was successful.
>+ * Note that we'll poll for up to 1ms (100
>cycles of 10us)
>+ * before giving up.
>+ */
>+
>+ port = data->acpi_data.status_register.address;
>+ bit_width = data->acpi_data.status_register.bit_width;
>+
>+ dprintk("Looking for 0x%08x from port 0x%04x\n",
>+ (u32)
>data->acpi_data.states[state].status, port);
>+
>+ for (i=0; i<100; i++) {
>+ ret = acpi_processor_read_port(port,
>bit_width, &value);
>+ if (ret) {
>+ dprintk("Invalid port width
>0x%04x\n", bit_width);
>+ retval = ret;
>+ goto migrate_end;
>+ }
>+ if (value == (u32)
>data->acpi_data.states[state].status)
>+ break;
>+ udelay(10);
> }
>- if (value == (u32) data->acpi_data.states[state].status)
>- break;
>- udelay(10);
>+ } else {
>+ i = 0;
>+ value = (u32) data->acpi_data.states[state].status;
> }
>
> /* notify cpufreq */
> cpufreq_notify_transition(&cpufreq_freqs, CPUFREQ_POSTCHANGE);
>
>- if (value != (u32) data->acpi_data.states[state].status) {
>+ if (unlikely(value != (u32)
>data->acpi_data.states[state].status)) {
> unsigned int tmp = cpufreq_freqs.new;
> cpufreq_freqs.new = cpufreq_freqs.old;
> cpufreq_freqs.old = tmp;
>@@ -537,6 +550,8 @@
> return;
> }
>
>+module_param(acpi_pstate_strict, uint, 0644);
>+MODULE_PARM_DESC(acpi_pstate_strict, "value 0 or non-zero.
>non-zero -> strict ACPI checks are performed during frequency
>changes.");
>
> late_initcall(acpi_cpufreq_init);
> module_exit(acpi_cpufreq_exit);
>
-
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