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From: Kai Heng Feng <kai.heng.feng@canonical.com>
To: Lukas Wunner <lukas@wunner.de>
Cc: Alan Stern <stern@rowland.harvard.edu>,
	Bjorn Helgaas <helgaas@kernel.org>,
	Rafael Wysocki <rafael.j.wysocki@intel.com>,
	linux-pci@vger.kernel.org, LKML <linux-kernel@vger.kernel.org>,
	Mathias Nyman <mathias.nyman@intel.com>,
	linux-usb@vger.kernel.org
Subject: Re: [PATCH] PCI / PM: Don't runtime suspend when device only supports wakeup from D0
Date: Thu, 23 May 2019 03:05:08 +0800	[thread overview]
Message-ID: <850CC1CD-2043-4C32-8BB1-5F5BAC1DDF55@canonical.com> (raw)
In-Reply-To: <20190522185339.pfo5xeopyz2i5iem@wunner.de>



> On May 23, 2019, at 2:53 AM, Lukas Wunner <lukas@wunner.de> wrote:
> 
> On Wed, May 22, 2019 at 02:39:56PM -0400, Alan Stern wrote:
>> According to Kai, PME signalling doesn't work in D0 -- or at least, it
>> is _documented_ not to work in D0 -- even though it is enabled and the
>> device claims to support it.
>> 
>> In any case, I don't really see any point in "runtime suspending" a 
>> device while leaving it in D0.  We might as well just leave it alone.
> 
> There may be devices whose drivers are able to reduce power consumption
> through some device-specific means when runtime suspending, even though
> the device remains in PCI_D0.  The patch would cause a power regression
> for those.
> 
> In particular, pci_target_state() returns PCI_D0 if the device lacks the
> PM capability.

So an explicit device_can_wakeup() check before calling pci_target_state()
is needed to avoid the case you described.

I’ll add this in patch v2.

Kai-Heng

> 
> Thanks,
> 
> Lukas


  reply	other threads:[~2019-05-22 19:05 UTC|newest]

Thread overview: 18+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-05-21 16:31 [PATCH] PCI / PM: Don't runtime suspend when device only supports wakeup from D0 Kai-Heng Feng
2019-05-21 22:23 ` Bjorn Helgaas
2019-05-22  3:42   ` Kai Heng Feng
2019-05-22 13:48     ` Bjorn Helgaas
2019-05-22 15:46       ` Kai Heng Feng
2019-05-22 18:11         ` Bjorn Helgaas
2019-05-22 18:39           ` Alan Stern
2019-05-22 18:53             ` Lukas Wunner
2019-05-22 19:05               ` Kai Heng Feng [this message]
2019-05-22 20:52             ` Bjorn Helgaas
2019-05-23  4:39               ` Kai-Heng Feng
2019-05-27 16:57                 ` Bjorn Helgaas
2019-06-05 11:57                   ` Bjorn Helgaas
2019-07-05  7:02                     ` Kai-Heng Feng
2019-07-05  9:39                       ` Rafael J. Wysocki
2019-07-05 13:51                         ` Kai-Heng Feng
2019-07-09 13:45                       ` Bjorn Helgaas
2019-09-02 13:47                         ` Kai-Heng Feng

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