Re: [PATCH v2] PCI: dwc: fix enumeration end when reaching root subordinate

From: Mika Westerberg <mika.westerberg@linux.intel.com>
To: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Cc: Koen Vandeputte <koen.vandeputte@ncentric.com>,
	linux-pci@vger.kernel.org,
	Binghui Wang <wangbinghui@hisilicon.com>,
	Bjorn Helgaas <bhelgaas@google.com>,
	Jesper Nilsson <jesper.nilsson@axis.com>,
	Jianguo Sun <sunjianguo1@huawei.com>,
	Jingoo Han <jingoohan1@gmail.com>,
	Kishon Vijay Abraham I <kishon@ti.com>,
	Lucas Stach <l.stach@pengutronix.de>,
	Minghuan Lian <minghuan.Lian@freescale.com>,
	Mingkai Hu <mingkai.hu@freescale.com>,
	Murali Karicheri <m-karicheri2@ti.com>,
	Pratyush Anand <pratyush.anand@gmail.com>,
	Richard Zhu <hongxing.zhu@nxp.com>,
	Roy Zang <tie-fei.zang@freescale.com>,
	Shawn Guo <shawn.guo@linaro.org>,
	Stanimir Varbanov <svarbanov@mm-sol.com>,
	Thomas Petazzoni <thomas.petazzoni@free-electrons.com>,
	Xiaowei Song <songxiaowei@hisilicon.com>,
	Zhou Wang <wangzhou1@hisilicon.com>
Subject: Re: [PATCH v2] PCI: dwc: fix enumeration end when reaching root subordinate
Date: Mon, 5 Feb 2018 22:06:48 +0200	[thread overview]
Message-ID: <20180205200648.GM27654@lahna.fi.intel.com> (raw)
In-Reply-To: <20180205191420.GA12397@red-moon>

On Mon, Feb 05, 2018 at 07:14:21PM +0000, Lorenzo Pieralisi wrote:
> On Mon, Jan 15, 2018 at 10:36:08AM +0100, Koen Vandeputte wrote:
> > The subordinate value indicates the highest bus number which can be
> > reached downstream though a certain device.
> > 
> > Commit a20c7f36bd3d ("PCI: Do not allocate more buses than available in
> > parent")
> > ensures that downstream devices cannot assign busnumbers higher than the
> > upstream device subordinate number, which was indeed illogical.
> > 
> > By default, dw_pcie_setup_rc() inits the Root Complex subordinate to a
> > value of 0x01.
> > 
> > Due to this combined with above commit, enumeration stops digging deeper
> > downstream as soon as bus num 0x01 has been assigned, which is always
> > the case for a bridge device.
> > 
> > This results in all devices behind a bridge bus to remain undetected, as
> > these would be connected to bus 0x02 or higher.
> > 
> > Fix this by initializing the RC to a subordinate value of 0xff, which is
> > not altering hardware behaviour in any way, but informs probing
> > function pci_scan_bridge() later on which reads this value back from
> > register.
> > 
> > Following nasty errors during boot are also fixed by this:
> > 
> > [    0.459145] pci_bus 0000:02: busn_res: can not insert [bus 02-ff]
> > under [bus 01] (conflicts with (null) [bus 01])
> > ...
> > [    0.464515] pci_bus 0000:03: [bus 03] partially hidden behind bridge
> > 0000:01 [bus 01]
> > ...
> > [    0.464892] pci_bus 0000:04: [bus 04] partially hidden behind bridge
> > 0000:01 [bus 01]
> > ...
> > [    0.466488] pci_bus 0000:05: [bus 05] partially hidden behind bridge
> > 0000:01 [bus 01]
> > [    0.466506] pci_bus 0000:02: busn_res: [bus 02-ff] end is updated to
> > 05
> > [    0.466517] pci_bus 0000:02: busn_res: can not insert [bus 02-05]
> > under [bus 01] (conflicts with (null) [bus 01])
> > [    0.466534] pci_bus 0000:02: [bus 02-05] partially hidden behind
> > bridge 0000:01 [bus 01]
> > 
> > Fixes: a20c7f36bd3d ("PCI: Do not allocate more buses than available in
> > parent")
> > Signed-off-by: Koen Vandeputte <koen.vandeputte@ncentric.com>
> > Tested-by: Niklas Cassel <niklas.cassel@axis.com>
> > Cc: Binghui Wang <wangbinghui@hisilicon.com>
> > Cc: Bjorn Helgaas <bhelgaas@google.com>
> > Cc: Jesper Nilsson <jesper.nilsson@axis.com>
> > Cc: Jianguo Sun <sunjianguo1@huawei.com>
> > Cc: Jingoo Han <jingoohan1@gmail.com>
> > Cc: Kishon Vijay Abraham I <kishon@ti.com>
> > Cc: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
> > Cc: Lucas Stach <l.stach@pengutronix.de>
> > Cc: Mika Westerberg <mika.westerberg@linux.intel.com>
> > Cc: Minghuan Lian <minghuan.Lian@freescale.com>
> > Cc: Mingkai Hu <mingkai.hu@freescale.com>
> > Cc: Murali Karicheri <m-karicheri2@ti.com>
> > Cc: Pratyush Anand <pratyush.anand@gmail.com>
> > Cc: Richard Zhu <hongxing.zhu@nxp.com>
> > Cc: Roy Zang <tie-fei.zang@freescale.com>
> > Cc: Shawn Guo <shawn.guo@linaro.org>
> > Cc: Stanimir Varbanov <svarbanov@mm-sol.com>
> > Cc: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
> > Cc: Xiaowei Song <songxiaowei@hisilicon.com>
> > Cc: Zhou Wang <wangzhou1@hisilicon.com>
> > ---
> >  drivers/pci/dwc/pcie-designware-host.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> I would appreciate some testing from dwc host maintainers so that
> we can merge this patch, it is a bug fix that should be merged as
> soon as possible, please help Koen test it and provide feedback
> on the list.

BTW, this should have a stable tag so that it gets backported to stable
kernels. I guess whoever is applying the patch can add it so no need for
another revision.