linux-kernel - Re: [PATCH v2 02/22] PCI/MSI: Remove useless bus->msi assignment

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Date:	Thu, 25 Sep 2014 09:06:01 +0200
From:	Thierry Reding <thierry.reding@...il.com>
To:	Yijing Wang <wangyijing@...wei.com>
Cc:	Bjorn Helgaas <bhelgaas@...gle.com>, linux-pci@...r.kernel.org,
	linux-kernel@...r.kernel.org, Xinwei Hu <huxinwei@...wei.com>,
	Wuyun <wuyun.wu@...wei.com>,
	linux-arm-kernel@...ts.infradead.org,
	Russell King <linux@....linux.org.uk>,
	linux-arch@...r.kernel.org, arnab.basu@...escale.com,
	Bharat.Bhushan@...escale.com, x86@...nel.org,
	Arnd Bergmann <arnd@...db.de>,
	Thomas Gleixner <tglx@...utronix.de>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	xen-devel@...ts.xenproject.org, Joerg Roedel <joro@...tes.org>,
	iommu@...ts.linux-foundation.org, linux-mips@...ux-mips.org,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	linuxppc-dev@...ts.ozlabs.org, linux-s390@...r.kernel.org,
	Sebastian Ott <sebott@...ux.vnet.ibm.com>,
	Tony Luck <tony.luck@...el.com>, linux-ia64@...r.kernel.org,
	"David S. Miller" <davem@...emloft.net>,
	sparclinux@...r.kernel.org, Chris Metcalf <cmetcalf@...era.com>,
	Ralf Baechle <ralf@...ux-mips.org>,
	Lucas Stach <l.stach@...gutronix.de>,
	David Vrabel <david.vrabel@...rix.com>,
	Sergei Shtylyov <sergei.shtylyov@...entembedded.com>,
	Michael Ellerman <mpe@...erman.id.au>,
	Thomas Petazzoni <thomas.petazzoni@...e-electrons.com>
Subject: Re: [PATCH v2 02/22] PCI/MSI: Remove useless bus->msi assignment

On Thu, Sep 25, 2014 at 11:14:12AM +0800, Yijing Wang wrote:
> Currently, PCI drivers will initialize bus->msi in
> pcibios_add_bus(). pcibios_add_bus() will be called
> in every pci bus initialization. So the bus->msi
> assignment in pci_alloc_child_bus() is useless.

I think this should be the other way around. The default should be to
inherit bus->msi from the parent. That way drivers don't typically have
to do it, yet they can still opt to override it if they need to.

For Tegra for example I think it would work if we assigned the MSI chip
to the root bus (in tegra_pcie_scan_bus()) and then have it propagated
to child busses in pci_alloc_child_bus() so that tegra_pcie_add_bus()
can be removed altogether.

Thierry

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