linux-kernel - Re: [PATCH v9 06/30] PCI: Separate pci_host_bridge creation out of pci_create_root

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Date:	Tue, 7 Apr 2015 16:38:39 -0500
From:	Bjorn Helgaas <bhelgaas@...gle.com>
To:	Yijing Wang <wangyijing@...wei.com>
Cc:	Jiang Liu <jiang.liu@...ux.intel.com>, linux-pci@...r.kernel.org,
	Yinghai Lu <yinghai@...nel.org>, linux-kernel@...r.kernel.org,
	Marc Zyngier <marc.zyngier@....com>,
	linux-arm-kernel@...ts.infradead.org,
	Russell King <linux@....linux.org.uk>, dja@...ens.net,
	x86@...nel.org, Thomas Gleixner <tglx@...utronix.de>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Rusty Russell <rusty@...tcorp.com.au>,
	Tony Luck <tony.luck@...el.com>, linux-ia64@...r.kernel.org,
	"David S. Miller" <davem@...emloft.net>,
	Guan Xuetao <gxt@...c.pku.edu.cn>, linux-alpha@...r.kernel.org,
	linux-m68k@...ts.linux-m68k.org, Liviu Dudau <liviu@...au.co.uk>,
	Arnd Bergmann <arnd@...db.de>,
	Geert Uytterhoeven <geert@...ux-m68k.org>
Subject: Re: [PATCH v9 06/30] PCI: Separate pci_host_bridge creation out of
 pci_create_root_bus()

On Fri, Apr 03, 2015 at 05:25:40PM +0800, Yijing Wang wrote:
> This patch separate pci_host_bridge creation out
> of pci_create_root_bus(), and try to make a generic
> pci_host_bridge, then we could make it hold host
> bridge specific operations like
> pcibios_root_bridge_prepare(). The changes are
> transparent to platform host bridge drivers.
> 
> Signed-off-by: Yijing Wang <wangyijing@...wei.com>
> ---
>  drivers/pci/host-bridge.c |   52 +++++++++++++++++++++
>  drivers/pci/pci.h         |    3 +
>  drivers/pci/probe.c       |  113 +++++++++++++++++++++------------------------
>  3 files changed, 108 insertions(+), 60 deletions(-)
> 
> diff --git a/drivers/pci/host-bridge.c b/drivers/pci/host-bridge.c
> index 39b2dbe..7d52a0a 100644
> --- a/drivers/pci/host-bridge.c
> +++ b/drivers/pci/host-bridge.c
> @@ -8,6 +8,58 @@
>  
>  #include "pci.h"
>  
> +static void pci_release_host_bridge_dev(struct device *dev)
> +{
> +	struct pci_host_bridge *bridge = to_pci_host_bridge(dev);
> +
> +	if (bridge->release_fn)
> +		bridge->release_fn(bridge);
> +
> +	pci_free_resource_list(&bridge->windows);
> +	kfree(bridge);
> +}
> +
> +struct pci_host_bridge *pci_create_host_bridge(
> +		struct device *parent, int domain, int bus,
> +		struct list_head *resources)
> +{
> +	int error;
> +	struct pci_host_bridge *host;
> +	struct resource_entry *window, *n;
> +
> +	host = kzalloc(sizeof(*host), GFP_KERNEL);
> +	if (!host)
> +		return NULL;
> +
> +	host->dev.parent = parent;
> +	INIT_LIST_HEAD(&host->windows);
> +	resource_list_for_each_entry_safe(window, n, resources)
> +		list_move_tail(&window->node, &host->windows);
> +	/*
> +	 * If support CONFIG_PCI_DOMAINS_GENERIC, use
> +	 * pci_host_assign_domain_nr() to update domain
> +	 * number.
> +	 */
> +	host->domain = domain;
> +	pci_host_assign_domain_nr(host);

I think it's a bit confusing that there's another "host->domain ="
assignment buried inside pci_host_assign_domain_nr(), so the first
assignment is overwritten when CONFIG_PCI_DOMAINS_GENERIC is set.

Can you do something like this instead:

  int pci_host_assign_domain_nr(struct pci_host_bridge *host, int domain)
  {
  #ifdef CONFIG_PCI_DOMAINS_GENERIC
    host->domain = pci_assign_domain_nr(host->dev.parent);
  #else
    host->domain = domain;
  #endif
  }

Then the alternatives (CONFIG_PCI_DOMAINS_GENERIC=y and
CONFIG_PCI_DOMAINS_GENERIC being unset) are close together and right at the
#ifdef CONFIG_PCI_DOMAINS_GENERIC, so no extra comments are needed.

Bjorn
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