Re: Patch "ahci: Allow setting a default LPM policy for mobile chipsets" has been added to the 4.14-stable tree

[Greg KH <gregkh@linuxfoundation.org>]

On Wed, Feb 14, 2018 at 04:03:17PM +0100, Hans de Goede wrote:
> Hi All,
> 
> On 14-02-18 15:25, gregkh@linuxfoundation.org wrote:
> > 
> > This is a note to let you know that I've just added the patch titled
> > 
> >      ahci: Allow setting a default LPM policy for mobile chipsets
> > 
> > to the 4.14-stable tree which can be found at:
> >      http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
> > 
> > The filename of the patch is:
> >       ahci-allow-setting-a-default-lpm-policy-for-mobile-chipsets.patch
> > and it can be found in the queue-4.14 subdirectory.
> > 
> > If you, or anyone else, feels it should not be added to the stable tree,
> > please let <stable@vger.kernel.org> know about it.
> 
> I wonder how this ended up on the patches-for-stable list? Torvald's
> master commits have neither a Cc: stable or a Fixes tag.
> 
> By itself this series is harmless, until someone actually sets
> the new Kconfig option to something other then 0.

See my response to the 4.15.y patch for "how" this came to be merged.

> > +config SATA_MOBILE_LPM_POLICY
> > +	int "Default SATA Link Power Management policy for mobile chipsets"
> > +	range 0 4
> > +	default 0
> > +	depends on SATA_AHCI
> > +	help
> > +	  Select the Default SATA Link Power Management (LPM) policy to use
> > +	  for mobile / laptop variants of chipsets / "South Bridges".
> > +
> > +	  The value set has the following meanings:
> > +		0 => Keep firmware settings
> > +		1 => Maximum performance
> > +		2 => Medium power
> > +		3 => Medium power with Device Initiated PM enabled
> > +		4 => Minimum power
> > +
> > +	  Note "Minimum power" is known to cause issues, including disk
> > +	  corruption, with some disks and should not be used.
> > +
> 
> AFAIK 4.14 and older do not have med_power_with_dipm, so setting this
> to 3 will lead to a setting of min_power. Which leads me to my worry
> about this series, as said in itself it is harmless, but as the help
> text says setting it to 4 (*) is dangerous. Actually this week I've
> received my first bug report that even med_power_with_dipm is causing
> issues (disconnects) with some devices. I'm working with the reporter
> an a blacklist entry for the specific SSD in question, but given that
> we're still figuring this out for master I wonder how wise it is to
> add these to stable, esp. since stable lacks med_power_with_dipm.
> 
> At a minimum we should fixup the help-text for 4.14 and older
> (4.15 does have med_power_with_dipm).

What would the text be for 4.14.y and older?  I'll be glad to fix that
up.  Or I can drop the whole thing and fit in the device id update "by
hand", if you think this shouldn't go to the stable trees.

thanks,

greg k-h