ata: libata-eh: Keep DIPM disabled while modifying the allowed LPM states

Currently, it is possible that LPM is enabled while calling the set_lpm()
callback.

The current code performs a SET FEATURES command to disable DIPM if
policy < ATA_LPM_MED_POWER_WITH_DIPM, this means that it will currently
disable DIPM for policies:
ATA_LPM_UNKNOWN, ATA_LPM_MAX_POWER, ATA_LPM_MED_POWER
(but not for policy ATA_LPM_MED_POWER_WITH_DIPM).

The code called after calling the set_lpm() callback will later perform
a SET FEATURES command to enable DIPM, if
policy >= ATA_LPM_MED_POWER_WITH_DIPM.

As we can see DIPM will not be disabled before calling set_lpm() if the LPM
policy is: ATA_LPM_MED_POWER_WITH_DIPM, ATA_LPM_MIN_POWER_WITH_PARTIAL,
or ATA_LPM_MIN_POWER.

Make sure that we always disable DIPM before calling the set_lpm()
callback. This is because the set_lpm() callback is the function (for AHCI)
that sets the proper bits in PxSCTL.IPM, reflecting the support of the HBA.
PxSCTL.IPM controls the LPM states that the device is allowed to enter.

If the device tries to enter a state disabled by PxSCTL.IPM, the host will
NAK the transition.

If we do not disable DIPM before modifying PxSCTL.IPM, it is possible that
DIPM will try (and will be allowed to) enter a LPM state that the HBA does
not support (since we have not yet written PxSCTL.IPM, the HBA wasn't able
to NAK the transition).

While at it, remove the guard of host support for DIPM around the disabling
of DIPM. While it makes sense to take host support for DIPM into account
when enabling DIPM, it makes zero sense to take host support into account
when disabling DIPM.

If the host does not support DIPM, that is an even bigger reason why DIPM
should be disabled on the device side.

Signed-off-by: Niklas Cassel <cassel@kernel.org>
Signed-off-by: Damien Le Moal <dlemoal@kernel.org>

Author: floatious

drivers/ata/libata-eh.c

@@ -3471,8 +3471,7 @@ static int ata_eh_set_lpm(struct ata_link *link, enum ata_lpm_policy policy,
 			hints &= ~ATA_LPM_HIPM;
 
 		/* disable DIPM before changing link config */
-		if (policy < ATA_LPM_MED_POWER_WITH_DIPM &&
-		    (dev_has_dipm && host_has_dipm)) {
+		if (dev_has_dipm) {
 			err_mask = ata_dev_set_feature(dev,
 					SETFEATURES_SATA_DISABLE, SATA_DIPM);
 			if (err_mask && err_mask != AC_ERR_DEV) {