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

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%3Ba=su...

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