Re: [PATCH 04/10] ata: libata-eh: Avoid unnecessary resets when revalidating devices

[Niklas Cassel <cassel@kernel.org>]

On Tue, Jul 01, 2025 at 03:48:15PM +0900, Damien Le Moal wrote:
> 
> There is a 10ms wait already in sata_link_scr_lpm() but it seems to not always
> be enough. The specs say that transitions out of HIPM "shall not take more than
> 10ms", but hey, we all know how devices always follow the specs, right ? :)

HIPM / ALPM includes Partial, Slumber and DevSleep.

10 ms is for Slumber.

DevSleep can be much longer than that:
          - DevSleep: The Phy logic may be powered down. The exit latency from
                      this state is no longer than 20 ms, unless otherwise
                      specified by DETO in the device Identify Device Data log.


From PxDEVSLP.DETO:
  Device Sleep Exit Timeout (DETO): This field specifies the maximum duration (in
  approximate 1ms granularity) from DEVSLP de-assertion until the device is ready to
  accept OOB. The nominal value is 20ms while the max value is 255ms depending
  on device identification information.


So technically it can be 255 ms :)


Note that we do actually read and save DETO:
https://github.com/torvalds/linux/blob/v6.16-rc4/drivers/ata/libahci.c#L2293-L2295

But like you said below, with this patch, we should be able to remove the sleep
if we wanted, so I don't think that we necessarily need to increase it.


> 
> > From a cursory glance we just continue, and (apparently) hope that
> > everything will be well eventually.
> > Hmm?
> 
> It is fine to continue because transitions out of DIPM/HIPM/DevSleep are
> automatic if you send a command. So we actually do not need to wait at all and
> probably can remove that 10ms sleep in sata_link_scr_lpm(). But I have not for now.