linux-kernel - Re: [PATCH v9 4/4] PCI: Allow extend_bridge_window() to shrink resource if necessary

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Date:   Wed, 30 Oct 2019 13:22:44 +0000
From:   Nicholas Johnson <nicholas.johnson-opensource@...look.com.au>
To:     "mika.westerberg@...ux.intel.com" <mika.westerberg@...ux.intel.com>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
        "bhelgaas@...gle.com" <bhelgaas@...gle.com>,
        "corbet@....net" <corbet@....net>,
        "benh@...nel.crashing.org" <benh@...nel.crashing.org>,
        "logang@...tatee.com" <logang@...tatee.com>
Subject: Re: [PATCH v9 4/4] PCI: Allow extend_bridge_window() to shrink
 resource if necessary

On Wed, Oct 30, 2019 at 02:07:05PM +0200, mika.westerberg@...ux.intel.com wrote:
> On Tue, Oct 29, 2019 at 03:29:21PM +0000, Nicholas Johnson wrote:
> > Remove checks for resource size in extend_bridge_window(). This is
> > necessary to allow the pci_bus_distribute_available_resources() to
> > function when the kernel parameter pci=hpmemsize=nn[KMG] is used to
> > allocate resources. Because the kernel parameter sets the size of all
> > hotplug bridges to be the same, there are problems when nested hotplug
> > bridges are encountered. Fitting a downstream hotplug bridge with size X
> > and normal bridges with non-zero size Y into parent hotplug bridge with
> > size X is impossible, and hence the downstream hotplug bridge needs to
> > shrink to fit into its parent.
> > 
> > Add check for if bridge is extended or shrunken and adjust pci_dbg to
> > reflect this.
> > 
> > Reset the resource if its new size is zero (if we have run out of a
> > bridge window resource) to prevent the PCI resource assignment code from
> > attempting to assign a zero-sized resource.
> > 
> > Rename extend_bridge_window() to adjust_bridge_window() to reflect the
> > fact that the window can now shrink.
> > 
> > Signed-off-by: Nicholas Johnson <nicholas.johnson-opensource@...look.com.au>
> > ---
> >  drivers/pci/setup-bus.c | 23 +++++++++++++++--------
> >  1 file changed, 15 insertions(+), 8 deletions(-)
> > 
> > diff --git a/drivers/pci/setup-bus.c b/drivers/pci/setup-bus.c
> > index fe8b2c715..f8cd54584 100644
> > --- a/drivers/pci/setup-bus.c
> > +++ b/drivers/pci/setup-bus.c
> > @@ -1814,7 +1814,7 @@ void __init pci_assign_unassigned_resources(void)
> >  	}
> >  }
> >  
> > -static void extend_bridge_window(struct pci_dev *bridge, struct resource *res,
> > +static void adjust_bridge_window(struct pci_dev *bridge, struct resource *res,
> >  				 struct list_head *add_list,
> >  				 resource_size_t new_size)
> >  {
> > @@ -1823,13 +1823,20 @@ static void extend_bridge_window(struct pci_dev *bridge, struct resource *res,
> >  	if (res->parent)
> >  		return;
> >  
> > -	if (resource_size(res) >= new_size)
> > -		return;
> > +	if (new_size > resource_size(res)) {
> > +		add_size = new_size - resource_size(res);
> > +		pci_dbg(bridge, "bridge window %pR extended by %pa\n", res,
> > +			&add_size);
> > +	} else if (new_size < resource_size(res)) {
> > +		add_size = resource_size(res) - new_size;
> > +		pci_dbg(bridge, "bridge window %pR shrunken by %pa\n", res,
> > +			&add_size);
> > +	}
> 
> Do we need to care about new_size == resource_size(res)?
Sorry, I skipped over this before re-posting. If we are not changing the 
size, does it need to be logged in pci_dbg? I could change it to ">=", 
meaning if the size does not change then it will be "extended" by 0 in 
pci_dbg.

Let me know if you wish for this to happen. But I am easy either way.

If you are fine with how it is, PATCH v10 should have addressed 
everything so far.
> 
> Also there are several calls of resource_size(res) above so probably
> worth storing it into a helper variable.
> 
> > -	add_size = new_size - resource_size(res);
> > -	pci_dbg(bridge, "bridge window %pR extended by %pa\n", res, &add_size);
> >  	res->end = res->start + new_size - 1;
> >  	remove_from_list(add_list, res);
> > +	if (!new_size)
> > +		reset_resource(res);
> >  }
Cheers