Re: [PATCH v2 07/10] ata: ahci: Disallow LPM policy control for external ports

[Niklas Cassel <cassel@kernel.org>]

On Tue, Jul 01, 2025 at 09:14:05AM +0900, Damien Le Moal wrote:
> Commit ae1f3db006b7 ("ata: ahci: do not enable LPM on external ports")
> added an early return in ahci_update_initial_lpm_policy() for all
> ports flagged as external with the ATA_PFLAG_EXTERNAL port flag (e.g.
> eSATA ports or hotplug capable ports) so that the target_lpm_policy of
> these ports is unchanged and set to ATA_LPM_UNKNOWN. thus forcing libata
> EH to not be called for external port. The goal of this change is to
> preserve the initial power management policy to not break the hotplug
> capability of external ports.
> 
> However, this change is incomplete as users or system daemon (e.g.
> systemd-udevd) can still apply the system preferred power management
> policy through sysfs, thus potentially unknowingly breaking the port
> hotplug capability.
> 
> Modify ahci_update_initial_lpm_policy() to flag external ports with
> ATA_FLAG_NO_LPM to prevent changes to the LPM policy by users through
> the sysfs link_power_management_policy host attribute. Also set the
> target_lpm_policy of external ports to ATA_LPM_MAX_POWER to ensure
> that the port is not in a low power state preventing hotplug operations.
> 
> Signed-off-by: Damien Le Moal <dlemoal@kernel.org>

Perhaps also mention that debug message is removed because since
commit 439d47608bb3 ("ata: libata: Print if port is external on boot")
it is printed unconditionally at boot.

With that:
Reviewed-by: Niklas Cassel <cassel@kernel.org>

> ---
>  drivers/ata/ahci.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/ata/ahci.c b/drivers/ata/ahci.c
> index 0760fa47d90e..a061aa3299ef 100644
> --- a/drivers/ata/ahci.c
> +++ b/drivers/ata/ahci.c
> @@ -1776,7 +1776,8 @@ static void ahci_update_initial_lpm_policy(struct ata_port *ap)
>  	 * LPM if the port advertises itself as an external port.
>  	 */
>  	if (ap->pflags & ATA_PFLAG_EXTERNAL) {
> -		ata_port_dbg(ap, "external port, not enabling LPM\n");
> +		ap->flags |= ATA_FLAG_NO_LPM;
> +		ap->target_lpm_policy = ATA_LPM_MAX_POWER;
>  		return;
>  	}
>  
> -- 
> 2.50.0
>