linux-kernel - Re: [PATCH v1 00/25] PCI: Request host bridge window resources

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Date:	Tue, 21 Jun 2016 10:03:52 -0500
From:	Bjorn Helgaas <helgaas@...nel.org>
To:	wangyijing <wangyijing@...wei.com>
Cc:	Bjorn Helgaas <bhelgaas@...gle.com>,
	Thomas Petazzoni <thomas.petazzoni@...e-electrons.com>,
	Jason Cooper <jason@...edaemon.net>,
	Scott Branden <sbranden@...adcom.com>,
	Jon Mason <jonmason@...adcom.com>, linux-pci@...r.kernel.org,
	Pratyush Anand <pratyush.anand@...il.com>,
	linux-kernel@...r.kernel.org, Ray Jui <rjui@...adcom.com>,
	rfi@...ts.rocketboards.org, linux-renesas-soc@...r.kernel.org,
	Simon Horman <horms@...ge.net.au>,
	Thierry Reding <thierry.reding@...il.com>,
	Tanmay Inamdar <tinamdar@....com>,
	Jingoo Han <jingoohan1@...il.com>, linux-tegra@...r.kernel.org,
	Ley Foon Tan <lftan@...era.com>,
	Michal Simek <michal.simek@...inx.com>,
	Sören Brinkmann <soren.brinkmann@...inx.com>,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v1 00/25] PCI: Request host bridge window resources

On Tue, Jun 21, 2016 at 07:58:08PM +0800, wangyijing wrote:
> Hi Bjorn, use devm_request_resource() for host bridge resource is cool,
> what about do the similar change for x86, now we request host bridge resource
> in pci_acpi_root_add_resources() in x86, and we would release the host bridge
> resource when host bridge device refcount reach 0. This logic may introduce issue,
> E.g.
> If we try to remove a pci host bridge, but there is a child pci device which refcount
> cannot decrease to 0 after remove the device, in this case, its parent pci_bus and
> parent device, all their refcount cannot reach to 0, the result is pci host bridge
> refcount can not reach 0, so its .release_fn() won't be called, and host bridge
> resouces can not release. If we want to add the pci host bridge again, all pci devices
> can not work because the resource is conflict with the old.
> 
> devm resource would be released when the driver detach, this is better than what we do now, I think.

I'm not going to convert pci_root.c to use devm right now.  That might
be a good thing, but this current series is mostly trivial.  I think
changing pci_root.c would not be trivial, so that looks like a project
all by itself.

I don't quite follow the example of removing a host bridge while a
child PCI device refcount is non-zero.  That sounds like an invalid
scenario regardless of whether the resources are released by a
.release_fn() or by devm.

Bjorn