linux-kernel - Re: [PATCH v4] sparc/PCI: Fix for panic while enabling SR-IOV

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Date:	Wed, 30 Mar 2016 14:37:06 -0500
From:	Bjorn Helgaas <helgaas@...nel.org>
To:	Babu Moger <babu.moger@...cle.com>
Cc:	David Miller <davem@...emloft.net>, bhelgaas@...gle.com,
	wangyijing@...wei.com, sowmini.varadhan@...cle.com,
	jiang.liu@...ux.intel.com, eric.snowberg@...cle.com,
	yinghai@...nel.org, dan.j.williams@...el.com,
	sparclinux@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-pci@...r.kernel.org, ethan.zhao@...cle.com
Subject: Re: [PATCH v4] sparc/PCI: Fix for panic while enabling SR-IOV

On Wed, Mar 30, 2016 at 10:31:18AM -0500, Babu Moger wrote:
> Hi David,
> 
> On 3/29/2016 7:57 PM, David Miller wrote:
> > From: Babu Moger <babu.moger@...cle.com>
> > Date: Thu, 24 Mar 2016 13:02:22 -0700
> > 
> >> We noticed this panic while enabling SR-IOV in sparc.
> >  ...
> >> SR-IOV code looks for arch specific data while enabling
> >> VFs. When VF device is added, driver probe function makes set
> >> of calls to initialize the pci device. Because the VF device is
> >> added different way than the normal PF device(which happens via
> >> of_create_pci_dev for sparc), some of the arch specific initialization
> >> does not happen for VF device.  That causes panic when archdata is
> >> accessed.
> >>
> >> To fix this, I have used already defined weak function
> >> pcibios_setup_device to copy archdata from PF to VF.
> >> Also verified the fix.
> >>
> >> Signed-off-by: Babu Moger <babu.moger@...cle.com>
> >> Signed-off-by: Sowmini Varadhan <sowmini.varadhan@...cle.com>
> >> Reviewed-by: Ethan Zhao <ethan.zhao@...cle.com>
> > 
> > Looks good, applied and queued up for -stable, thanks.
> 
> Thanks.
> 
> > 
> > Just a note, I am assuming that the VFs are not instantiated in the
> > device tree.  Because when you just memcpy the arch data over from the
> > PF, one thing we end up doing is using the device node of the PF.
> 
> No. VFs are not instantiated in device tree(/proc/device-tree)
> 
> > 
> > I slightly cringed at the memcpy, because at least one of these
> > pointers are to objects which are reference counted, the OF device.
> > 
> > Generally speaking we don't really support hot-plug for OF probed
> > devices, but if we did all of the device tree pointers have to be
> > refcounted properly.
> > 
> > So in the long term that whole sequence where we go:
> > 
> > 	struct dev_archdata *sd;
> >  ...
> > 	sd = &dev->dev.archdata;
> > 	sd->iommu = pbm->iommu;
> > 	sd->stc = &pbm->stc;
> > 	sd->host_controller = pbm;
> > 	sd->op = op = of_find_device_by_node(node);
> > 	sd->numa_node = pbm->numa_node;
> > 
> > should be encapsulated into a helper function, and both
> > of_create_pci_dev() and this new pcibios_setup_device() can
> > invoke it.
> > 
> 
> Yes. Agree. We need to refactor the whole of_create_pci_dev path to support
> hot-plug for the long term. I will start looking at it. For now we should be
> fine with the current patch. thanks

of_create_pci_dev() duplicates a lot of the code in
pci_setup_device().  I wish we didn't have to do that
because it's easy to let them get out of sync, but I
don't know if there are any reasonable alternatives.

I've wondered in the past whether it would be possible
to use the pci_setup_device() path on sparc & powerpc by
writing PCI config accessors that look up OF properties
as needed to fabricate responses to config reads.  Several
of the drivers in drivers/pci/host/* do a little bit of
this fabrication, although I don't think any go to the
extent of using OF.

Bjorn