netdev - Re: [PATCH] PCI: Reprogram bridge prefetch registers on resume

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Message-ID: <20180907150515.GA28739@al>
Date:   Fri, 7 Sep 2018 17:05:15 +0200
From:   Peter Wu <peter@...ensteyn.nl>
To:     Daniel Drake <drake@...lessm.com>
Cc:     bhelgaas@...gle.com, linux-pci@...r.kernel.org, linux@...lessm.com,
        nouveau@...ts.freedesktop.org, linux-pm@...r.kernel.org,
        kherbst@...hat.com, andriy.shevchenko@...ux.intel.com,
        rafael.j.wysocki@...el.com, keith.busch@...el.com,
        mika.westerberg@...ux.intel.com, jonathan.derrick@...el.com,
        kugel@...kbox.org, davem@...emloft.net, hkallweit1@...il.com,
        netdev@...r.kernel.org, nic_swsd@...ltek.com
Subject: Re: [PATCH] PCI: Reprogram bridge prefetch registers on resume

On Fri, Sep 07, 2018 at 01:36:14PM +0800, Daniel Drake wrote:
<..>
> Thomas Martitz reports that this workaround also solves an issue where
> the AMD Radeon Polaris 10 GPU on the HP Zbook 14u G5 is unresponsive
> after S3 suspend/resume.

Where was this claimed? It is not stated in the linked bug:
(https://bugs.freedesktop.org/show_bug.cgi?id=105760

> On resume, reprogram the PCI bridge prefetch registers, including the
> magic register mentioned above.
> 
> This matches Win10 behaviour, which also rewrites these registers
> during S3 resume (checked with qemu tracing).

Windows 10 unconditionally rewrites these registers (BAR, I/O Base +
Limit, Memory Base + Limit, etc. from top to bottom), see annotations:
https://www.spinics.net/lists/linux-pci/msg75856.html

Linux has a generic "restore" operation that works backwards from the
end of the PCI config space to the beginning, see
pci_restore_config_space. Do you have a dmesg where you see the
"restoring config space at offset" messages?

Would it be reasonable to unconditionally write these registers in
pci_restore_config_dword, like Windows does?

Kind regards,
Peter