Hi,

I'm having some problems with the link_power_management_policy on my
Dell XPS13 9333.
Changing policy from min_power or medium_power to max_performance
causes the following errors:

[ 3955.667086] ahci 0000:00:1f.2: port does not support device sleep
[ 3958.257106] ata3.00: exception Emask 0x10 SAct 0x40 SErr 0x50000 action 0xe 
frozen
[ 3958.257110] ata3.00: irq_stat 0x00400000, PHY RDY changed
[ 3958.257113] ata3: SError: { PHYRdyChg CommWake }
[ 3958.257116] ata3.00: failed command: READ FPDMA QUEUED
[ 3958.257120] ata3.00: cmd 60/00:30:c8:60:10/01:00:1d:00:00/40 tag 6 ncq 
131072 in
         res 40/00:34:c8:60:10/00:00:1d:00:00/40 Emask 0x10 (ATA bus error)
[ 3958.257122] ata3.00: status: { DRDY }
[ 3958.257126] ata3: hard resetting link
[ 3958.981727] ata3: SATA link up 6.0 Gbps (SStatus 133 SControl 300)
[ 3958.984994] ata3.00: configured for UDMA/133
[ 3958.997686] ahci 0000:00:1f.2: port does not support device sleep
[ 3958.997698] ata3: EH complete

Sometimes I get "failed command: WRITE FPDMA QUEUED" multiple times.

As far as I know, this had always happened and it was confirmed
by another user. I've also come across some logs of the same system
and saw the same errors here and there, so it shouldn't be a problem
of my laptop in particular.

What I find interesting is that transitions from min_power to
medium_power and vice versa do not cause these errors. There are only
problem switching from min_power and medium_power to max_performance.
Doing the opposite, i.e. from max_performance to min_power or
medium_power, seems to work fine.

As a consequence of these continuous errors, the speed is reduced
from 6.0 Gbps to 1.5 Gbps.

I'd prefer not to disable LPM as it saves a considerable amount of
power when I'm using the battery. For this reason I'm currently using
medium_power and min_power only to prevent errors.

Is it normal that these errors appears only when I switch to
max_performance? Was something similar observed on other systems?

Thanks,
Gabriele
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