linux-kernel - Re: [PATCH v8 4/6] PCI: Allow extend_bridge_window() to shrink resource if necessary

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Date:   Tue, 8 Oct 2019 15:09:07 +0300
From:   "mika.westerberg@...ux.intel.com" <mika.westerberg@...ux.intel.com>
To:     Nicholas Johnson <nicholas.johnson-opensource@...look.com.au>
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 v8 4/6] PCI: Allow extend_bridge_window() to shrink
 resource if necessary

On Fri, Jul 26, 2019 at 12:54:22PM +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 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.

Maybe you could show the topology here which needs shrinking.

> 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). If it is set to zero size and left, it can
> cause significant problems when it comes to enabling devices.

Same comment here about explaining the "significant problems".
> 
> Signed-off-by: Nicholas Johnson <nicholas.johnson-opensource@...look.com.au>
> ---
>  drivers/pci/setup-bus.c | 16 +++++++++++-----
>  1 file changed, 11 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/pci/setup-bus.c b/drivers/pci/setup-bus.c
> index a072781ab..7e1dc892a 100644
> --- a/drivers/pci/setup-bus.c
> +++ b/drivers/pci/setup-bus.c
> @@ -1823,13 +1823,19 @@ static void extend_bridge_window(struct pci_dev *bridge, struct resource *res,

Since it is also shrinking now maybe name it adjust_bridge_window() instead?