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SubjectRe: [PATCH] libata: Add new med_power_with_dipm link_power_management_policy setting
On Thu, Sep 14, 2017 at 12:35:36PM +0200, Hans de Goede wrote:
> As described by Matthew Garret quite a while back:
> https://mjg59.dreamwidth.org/34868.html
>
> Intel CPUs starting with the Haswell generation need SATA links to power
> down for the "package" part of the CPU to reach low power-states like
> PC7 / P8 which bring a significant power-saving with them.
>
> The default max_performance lpm policy does not allow for these high
> PC states, both the medium_power and min_power policies do allow this.
>
> The min_power policy saves significantly more power, but there are some
> reports of some disks / SSDs not liking min_power leading to system
> crashes and in some cases even data corruption has been reported.
>
> Matthew has found a document documenting the default settings of
> Intel's IRST Windows driver with which most laptops ship:
> https://www-ssl.intel.com/content/dam/doc/reference-guide/sata-devices-implementation-recommendations.pdf
>
> Matthew wrote a patch changing med_power to match those defaults, but
> that never got anywhere as some people where reporting issues with the
> patch-set that patch was a part of.
>
> This commit is another attempt to make the default IRST driver settings
> available under Linux, but instead of changing medium_power and
> potentially introducing regressions, this commit adds a new
> med_power_with_dipm setting which is identical to the existing
> medium_power accept that it enables dipm on top, which makes it match
> the Windows IRST driver settings, which should hopefully be safe to
> use on most devices.
>
> The med_power_with_dipm setting is close to min_power, except that:
> a) It does not use host-initiated slumber mode (ASP not set),
> but it does allow device-initiated slumber
> b) It does not enable DevSlp mode
>
> On my T440s test laptop I get the following power savings when idle:
> medium_power 0.9W
> med_power_with_dipm 1.2W
> min_power 1.2W
>
> Suggested-by: Matthew Garrett <mjg59@srcf.ucam.org>
> Cc: Matthew Garrett <mjg59@srcf.ucam.org>
> Signed-off-by: Hans de Goede <hdegoede@redhat.com>

Applied to libata/for-4.15.

Thanks.

--
tejun

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