[PATCH AUTOSEL 4.4 18/47] ata: libahci: Correct setting of DEVSLP register

[Sasha Levin]

From: Srinivas Pandruvada <srinivas.pandruvada@xxxxxxxxxxxxxxx>

[ Upstream commit 2dbb3ec29a6c069035857a2fc4c24e80e5dfe3cc ]

We have seen that on some platforms, SATA device never show any DEVSLP
residency. This prevent power gating of SATA IP, which prevent system
to transition to low power mode in systems with SLP_S0 aka modern
standby systems. The PHY logic is off only in DEVSLP not in slumber.
Reference:
https://www.intel.com/content/dam/www/public/us/en/documents/datasheets
/332995-skylake-i-o-platform-datasheet-volume-1.pdf
Section 28.7.6.1

Here driver is trying to do read-modify-write the devslp register. But
not resetting the bits for which this driver will modify values (DITO,
MDAT and DETO). So simply reset those bits before updating to new values.

Signed-off-by: Srinivas Pandruvada <srinivas.pandruvada@xxxxxxxxxxxxxxx>
Reviewed-by: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>
Reviewed-by: Hans de Goede <hdegoede@xxxxxxxxxx>
Signed-off-by: Tejun Heo <tj@xxxxxxxxxx>
Signed-off-by: Sasha Levin <alexander.levin@xxxxxxxxxxxxx>
---
 drivers/ata/libahci.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/ata/libahci.c b/drivers/ata/libahci.c
index 9628fa131757..8116cb2fef2d 100644
--- a/drivers/ata/libahci.c
+++ b/drivers/ata/libahci.c
@@ -2113,6 +2113,8 @@ static void ahci_set_aggressive_devslp(struct ata_port *ap, bool sleep)
 		deto = 20;
 	}
 
+	/* Make dito, mdat, deto bits to 0s */
+	devslp &= ~GENMASK_ULL(24, 2);
 	devslp |= ((dito << PORT_DEVSLP_DITO_OFFSET) |
 		   (mdat << PORT_DEVSLP_MDAT_OFFSET) |
 		   (deto << PORT_DEVSLP_DETO_OFFSET) |
-- 
2.17.1