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From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To: Lukas Wunner <lukas@wunner.de>
Cc: Mathias Nyman <mathias.nyman@linux.intel.com>,
	Mason <slash.tmp@free.fr>,
	Felipe Balbi <felipe.balbi@linux.intel.com>,
	linux-pci <linux-pci@vger.kernel.org>,
	linux-usb <linux-usb@vger.kernel.org>,
	Linux ARM <linux-arm-kernel@lists.infradead.org>,
	Bjorn Helgaas <helgaas@kernel.org>,
	Alan Stern <stern@rowland.harvard.edu>
Subject: Re: Possible regression between 4.9 and 4.13
Date: Tue, 29 Aug 2017 16:47:25 +0200	[thread overview]
Message-ID: <20170829144725.GB22532@kroah.com> (raw)
In-Reply-To: <20170829133852.GA13355@wunner.de>

On Tue, Aug 29, 2017 at 03:38:52PM +0200, Lukas Wunner wrote:
> On Tue, Aug 29, 2017 at 04:28:53PM +0300, Mathias Nyman wrote:
> > Then again it might be a bit too drastic to kill xhci just because
> > we read 0xffffffff once from a mmio xhci register. Maybe we should
> > return an error a couple times before actually tearing down xhci.
> > 
> > This tight check was originally done to detect pci hotplug removed
> > hosts as soon as possible.
> 
> Just make pci_dev_is_disconnected() public to detect PCI hot removal.
> We *know* when the device was hot removed, so I think there's no need
> to guess that based on reading "all ones" from mmio (which may happen
> for entirely legitimate reasons unrelated to hot removal).

No, you don't always "know" when a device is removed, don't rely on it,
not all platforms support that.

One more reason why I hate that function and I'm glad it's not exported
for others to think it somehow actually works for their system...

Reading all ff shows the device is removed, that's all the PCI spec
guarantees.  What other legitimate reason could that happen for?

thanks,

greg k-h

WARNING: multiple messages have this Message-ID (diff)
From: gregkh@linuxfoundation.org (Greg Kroah-Hartman)
To: linux-arm-kernel@lists.infradead.org
Subject: Possible regression between 4.9 and 4.13
Date: Tue, 29 Aug 2017 16:47:25 +0200	[thread overview]
Message-ID: <20170829144725.GB22532@kroah.com> (raw)
In-Reply-To: <20170829133852.GA13355@wunner.de>

On Tue, Aug 29, 2017 at 03:38:52PM +0200, Lukas Wunner wrote:
> On Tue, Aug 29, 2017 at 04:28:53PM +0300, Mathias Nyman wrote:
> > Then again it might be a bit too drastic to kill xhci just because
> > we read 0xffffffff once from a mmio xhci register. Maybe we should
> > return an error a couple times before actually tearing down xhci.
> > 
> > This tight check was originally done to detect pci hotplug removed
> > hosts as soon as possible.
> 
> Just make pci_dev_is_disconnected() public to detect PCI hot removal.
> We *know* when the device was hot removed, so I think there's no need
> to guess that based on reading "all ones" from mmio (which may happen
> for entirely legitimate reasons unrelated to hot removal).

No, you don't always "know" when a device is removed, don't rely on it,
not all platforms support that.

One more reason why I hate that function and I'm glad it's not exported
for others to think it somehow actually works for their system...

Reading all ff shows the device is removed, that's all the PCI spec
guarantees.  What other legitimate reason could that happen for?

thanks,

greg k-h

  reply	other threads:[~2017-08-29 14:47 UTC|newest]

Thread overview: 60+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-08-22 17:34 Possible regression between 4.9 and 4.13 Mason
2017-08-22 17:34 ` Mason
2017-08-23  6:07 ` Felipe Balbi
2017-08-23  6:07   ` Felipe Balbi
2017-08-23  7:51   ` Mathias Nyman
2017-08-23  7:51     ` Mathias Nyman
2017-08-23  9:18     ` Mason
2017-08-23  9:18       ` Mason
2017-08-23  9:31     ` Mason
2017-08-23  9:31       ` Mason
2017-08-23 11:11       ` Mathias Nyman
2017-08-23 11:11         ` Mathias Nyman
2017-08-23 11:54         ` Mason
2017-08-23 11:54           ` Mason
2017-08-23 12:41           ` Mason
2017-08-23 12:41             ` Mason
2017-08-23 14:30             ` Mason
2017-08-23 14:30               ` Mason
2017-08-28  8:39               ` Mathias Nyman
2017-08-28  8:39                 ` Mathias Nyman
2017-08-28 14:40                 ` Mason
2017-08-28 14:40                   ` Mason
2017-08-29 13:28                   ` Mathias Nyman
2017-08-29 13:28                     ` Mathias Nyman
2017-08-29 13:38                     ` Lukas Wunner
2017-08-29 13:38                       ` Lukas Wunner
2017-08-29 14:47                       ` Greg Kroah-Hartman [this message]
2017-08-29 14:47                         ` Greg Kroah-Hartman
2017-08-29 15:34                         ` Lukas Wunner
2017-08-29 15:34                           ` Lukas Wunner
2017-08-29 15:51                           ` Greg Kroah-Hartman
2017-08-29 15:51                             ` Greg Kroah-Hartman
2017-08-30  6:36                             ` Lukas Wunner
2017-08-30  6:36                               ` Lukas Wunner
2017-08-30  6:45                               ` Greg Kroah-Hartman
2017-08-30  6:45                                 ` Greg Kroah-Hartman
2017-08-29 23:53                     ` Lukas Wunner
2017-08-29 23:53                       ` Lukas Wunner
2017-08-30  6:02                       ` Greg Kroah-Hartman
2017-08-30  6:02                         ` Greg Kroah-Hartman
2017-08-30  8:55                         ` Mason
2017-08-30  8:55                           ` Mason
2017-08-30  9:06                           ` Greg Kroah-Hartman
2017-08-30  9:06                             ` Greg Kroah-Hartman
2017-08-31  9:39                             ` Mason
2017-08-31  9:39                               ` Mason
2017-08-31 11:40                               ` Mathias Nyman
2017-08-31 11:40                                 ` Mathias Nyman
2017-08-30  9:07                           ` Ard Biesheuvel
2017-08-30  9:07                             ` Ard Biesheuvel
2017-08-30  9:22                             ` Greg Kroah-Hartman
2017-08-30  9:22                               ` Greg Kroah-Hartman
2017-08-30  9:37                             ` Mason
2017-08-30  9:37                               ` Mason
2017-08-31  9:17                               ` Mason
2017-08-31  9:17                                 ` Mason
2017-08-31 11:38                                 ` Mathias Nyman
2017-08-31 11:38                                   ` Mathias Nyman
2017-08-23 10:19     ` Mason
2017-08-23 10:19       ` Mason

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