Re: [PATCH v2 3/6] ata: libata-sata: Improve link_power_management_supported sysfs attribute

[Niklas Cassel <cassel@kernel.org>]

On Mon, Jan 12, 2026 at 04:05:18PM +0100, Damien Le Moal wrote:
> On 1/12/26 15:39, Niklas Cassel wrote:
> > I'm not sure if we should set sysfs attribute
> > link_power_management_supported == false if ATA_LFLAG_NO_LPM is set
> > (Currently we don't). Because if so, the sysfs supported attribute could
> > potentially change value during runtime, isn't it supposed to be static?
> > 
> > If we really want to, I guess we could do something like:
> > 
> > diff --git a/drivers/ata/libata-sata.c b/drivers/ata/libata-sata.c
> > index 04e1e774645e..1134943f49ae 100644
> > --- a/drivers/ata/libata-sata.c
> > +++ b/drivers/ata/libata-sata.c
> > @@ -913,6 +913,8 @@ static bool ata_scsi_lpm_supported(struct ata_port *ap)
> >  		return false;
> >  
> >  	ata_for_each_link(link, ap, EDGE) {
> > +		if (link->flags & ATA_LFLAG_NO_LPM)
> > +			return false;
> 
> Yeah, I think we need this. NO_LPM == max power, but cannot be changed. That's
> the same as for external ports. So we should report not supported so that
> userspace cannot change it.

ata_scsi_lpm_supported() already checks port flag ATA_FLAG_NO_LPM:

https://github.com/torvalds/linux/blob/v6.19-rc5/drivers/ata/libata-sata.c#L912-L913


Port flag ATA_FLAG_NO_LPM:
call .set_lpm() with ATA_LPM_MAX_POWER.

Link flag ATA_LFLAG_NO_LPM:
we called .set_lpm() on
the port, but the device disappeared from the port when doing so,
so make futher calls to set_lpm() for this link a no-op...
(No idea why it doesn't instead call set_lpm() with ATA_LPM_MAX_POWER?)



Kind regards,
Niklas