linux-kernel - Re: [PATCH 11/12] PM: i2c-designware-platdrv: Optimize power management

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Date:   Thu, 26 Oct 2017 22:41:40 +0200
From:   Wolfram Sang <wsa@...-dreams.de>
To:     "Rafael J. Wysocki" <rjw@...ysocki.net>
Cc:     Linux PM <linux-pm@...r.kernel.org>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Alan Stern <stern@...land.harvard.edu>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Linux ACPI <linux-acpi@...r.kernel.org>,
        Linux PCI <linux-pci@...r.kernel.org>,
        Linux Documentation <linux-doc@...r.kernel.org>,
        Mika Westerberg <mika.westerberg@...ux.intel.com>,
        Ulf Hansson <ulf.hansson@...aro.org>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Kevin Hilman <khilman@...nel.org>, linux-i2c@...r.kernel.org,
        Lee Jones <lee.jones@...aro.org>
Subject: Re: [PATCH 11/12] PM: i2c-designware-platdrv: Optimize power
 management

On Mon, Oct 16, 2017 at 03:31:17AM +0200, Rafael J. Wysocki wrote:
> From: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> 
> Optimize the power management in i2c-designware-platdrv by making it
> set the DPM_FLAG_SMART_SUSPEND and DPM_FLAG_LEAVE_SUSPENDED which
> allows some code to be dropped from its PM callbacks.
> 
> First, setting DPM_FLAG_SMART_SUSPEND causes the intel-lpss driver
> to avoid resuming i2c-designware-platdrv devices in its ->prepare
> callback, so they can stay in runtime suspend after that point even
> if the direct-complete feature is not used for them.
> 
> It also causes the PM core to avoid invoking "late" and "noirq"
> suspend callbacks for these devices if they are in runtime suspend
> at the beginning of the "late" phase of device suspend during
> system suspend.  That guarantees dw_i2c_plat_suspend() to be
> called for a device only if it is not in runtime suspend.
> Moreover, it also causes the PM core to set the device's runtime
> PM status to "active" after calling dw_i2c_plat_resume() for
> it, so the driver doesn't need internal flags to avoid invoking
> either dw_i2c_plat_suspend() or dw_i2c_plat_resume() twice in
> a row.
> 
> Second, setting DPM_FLAG_LEAVE_SUSPENDED enables the optimization
> allowing the device to stay suspended after system resume under
> suitable conditions, so again the driver doesn't need to take
> care of that by itself.
> 
> Accordingly, the internal "suspended" and "skip_resume" flags
> used by the driver are not necessary any more, so drop them and
> simplify the driver's PM callbacks.
> 
> Additionally, notice that dw_i2c_plat_complete() only needs
> to schedule runtime PM for the device if platform firmware
> has been involved in resuming the system, so make it call
> pm_resume_via_firmware() to check that.
> 
> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>

So, if the designware maintainers ack it, I will, too.


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