ahci: Allow setting a default LPM policy for mobile chipsets
On many laptops setting a different LPM policy then unknown /
max_performance can lead to power-savings of 1.0 - 1.5 Watts (when idle).
Modern ultrabooks idle around 6W (at 50% screen brightness), 1.0 - 1.5W
is a significant chunk of this.
There are some performance / latency costs to enabling LPM by default,
so it is desirable to make it possible to set a different LPM policy
for mobile / laptop variants of chipsets / "South Bridges" vs their
desktop / server counterparts. Also enabling LPM by default is not
entirely without risk of regressions. At least min_power is known to
cause issues with some disks, including some reports of data corruption.
This commits adds a new ahci.mobile_lpm_policy kernel cmdline option,
which defaults to a new SATA_MOBILE_LPM_POLICY Kconfig option so that
Linux distributions can choose to set a LPM policy for mobile chipsets
by default.
The reason to have both a kernel cmdline option and a Kconfig default
value for it, is to allow easy overriding of the default to allow
trouble-shooting without needing to rebuild the kernel.
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
diff --git a/drivers/ata/ahci.h b/drivers/ata/ahci.h
index 749fd94..a9d996e 100644
--- a/drivers/ata/ahci.h
+++ b/drivers/ata/ahci.h
@@ -251,6 +251,9 @@ enum {
AHCI_HFLAG_YES_ALPM = (1 << 23), /* force ALPM cap on */
AHCI_HFLAG_NO_WRITE_TO_RO = (1 << 24), /* don't write to read
only registers */
+ AHCI_HFLAG_IS_MOBILE = (1 << 25), /* mobile chipset, use
+ SATA_MOBILE_LPM_POLICY
+ as default lpm_policy */
/* ap->flags bits */