Re: [RFC PATCH] ata: ahci: Enable DEVSLP by default on x86 modern standby platform

From: Tejun Heo
Date: Mon Jul 02 2018 - 16:22:01 EST

On Mon, Jul 02, 2018 at 12:08:45PM -0700, Srinivas Pandruvada wrote:
> From: Srinivas <srinivas.pandruvada@xxxxxxxxxxxxxxx>
> One of the requirement for modern x86 system to enter lowest power mode
> (SLP_S0) is SATA IP block to be off. This is true even during when
> platform is suspended to idle and not only in opportunistic (runtime)
> suspend.
> Several of these system don't have traditional ACPI S3, so it is
> important that they enter SLP_S0 state, to avoid draining battery even
> during suspend even with out of the box Linux installation.
> SATA IP block doesn't get turned off till SATA is in DEVSLP mode. Here
> user has to either use scsi-host sysfs or tools like powertop to set
> the sata-host link_power_management_policy to min_power.
> This change sets by default link power management policy to min_power
> for some platforms. To avoid regressions, the following conditions
> are used:
> - The kernel config is already set to use med_power_with_dipm or deeper
> - System is a modern standby system using ACPI low power idle flag
> - The platform is not blacklisted for Suspend to Idle and suspend
> to idle is used instead of S3
> This combination will make sure that systems are fairly recent and
> since getting shipped with modern standby standby, the DEVSLP function
> is already validated.
> Signed-off-by: Srinivas Pandruvada <srinivas.pandruvada@xxxxxxxxxxxxxxx>

Seems sane to me. Hans, what do you think?