linux-kernel - Re: [PATCH 6/7] PM: i2c-designware-platdrv: Optimize power management

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Date:   Mon, 8 Jan 2018 15:36:33 +0100
From:   Wolfram Sang <wsa@...-dreams.de>
To:     Jarkko Nikula <jarkko.nikula@...ux.intel.com>
Cc:     "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Linux PM <linux-pm@...r.kernel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Alan Stern <stern@...land.harvard.edu>,
        Kevin Hilman <khilman@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Mika Westerberg <mika.westerberg@...ux.intel.com>,
        Ulf Hansson <ulf.hansson@...aro.org>,
        linux-i2c <linux-i2c@...r.kernel.org>,
        Linux PCI <linux-pci@...r.kernel.org>,
        Lee Jones <lee.jones@...aro.org>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Subject: Re: [PATCH 6/7] PM: i2c-designware-platdrv: Optimize power management

On Mon, Jan 08, 2018 at 04:31:58PM +0200, Jarkko Nikula wrote:
> On 01/03/2018 02:37 AM, 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 ACPI PM domain and 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 causes the device's runtime PM status to be set 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 resume for the device if platform firmware
> > has been involved in resuming the system, so make it call
> > pm_resume_via_firmware() to check that.  Also make it check the
> > runtime PM status of the device instead of its direct_complete
> > flag which also works if the device remained suspended due to
> > the DPM_FLAG_LEAVE_SUSPENDED driver flag.
> > 
> > Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> > ---
> >   drivers/i2c/busses/i2c-designware-core.h    |    2 -
> >   drivers/i2c/busses/i2c-designware-platdrv.c |   31 ++++++++++------------------
> >   2 files changed, 12 insertions(+), 21 deletions(-)
> > 
> This doesn't apply to linux-next due 0326f9f801b2 ("i2c: designware: rename
> i2c_dw_plat_prepare_clk to i2c_dw_prepare_clk"). It was trivial to fix which
> I did locally for testing.
> 
> Acked-by: Jarkko Nikula <jarkko.nikula@...ux.intel.com>

Acked-by: Wolfram Sang <wsa@...-dreams.de>


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