linux-kernel - Re: [PATCH v0 06/10] arm: orion5x: Add DT-based support for Netgear WNR854T

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Message-ID: <20160718114424.14a28889@free-electrons.com>
Date:	Mon, 18 Jul 2016 11:44:24 +0200
From:	Thomas Petazzoni <thomas.petazzoni@...e-electrons.com>
To:	Arnd Bergmann <arnd@...db.de>
Cc:	Jamie Lentin <jm@...tin.co.uk>, Andrew Lunn <andrew@...n.ch>,
	Florian Fainelli <f.fainelli@...il.com>,
	Jason Cooper <jason@...edaemon.net>,
	devicetree@...r.kernel.org, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Gregory Clement <gregory.clement@...e-electrons.com>,
	Imre Kaloz <kaloz@...nwrt.org>,
	linux-arm-kernel@...ts.infradead.org,
	Sebastian Hesselbarth <sebastian.hesselbarth@...il.com>
Subject: Re: [PATCH v0 06/10] arm: orion5x: Add DT-based support for Netgear
 WNR854T

Hello,

On Sun, 17 Jul 2016 22:41:35 +0200, Arnd Bergmann wrote:

> I would assume that the PCIe port should work out of the box with the driver

Unfortunately, no. The PCIe on Orion5x requires a workaround for
reading/writing the PCI configuration space. Instead of doing MMIO
accesses to PCIE_CONF_ADDR_OFF / PCIE_CONF_DATA_OFF, you must map a
MBus window, which provides a memory-mapped view of the PCI
configuration space.

Definitely not impossible to implement, but the driver doesn't work
as-is.

> We also don't seem to need any MBUS window setup for the I/O and
> memory spaces, which greatly simplifies the driver compared to the
> pci-mvebu one, it would be a fairly straightforward implementation
> based on pci-host-generic.c (which unfortunately just got way
> more complicated and might need to go on a diet).

MBus windows are needed. See:

        mvebu_mbus_add_window_remap_by_id(ORION_MBUS_PCI_IO_TARGET,
                                          ORION_MBUS_PCI_IO_ATTR,
                                          ORION5X_PCI_IO_PHYS_BASE,
                                          ORION5X_PCI_IO_SIZE,
                                          ORION5X_PCI_IO_BUS_BASE);
        mvebu_mbus_add_window_by_id(ORION_MBUS_PCI_MEM_TARGET,
                                    ORION_MBUS_PCI_MEM_ATTR,
                                    ORION5X_PCI_MEM_PHYS_BASE,
                                    ORION5X_PCI_MEM_SIZE);

in orion5x_setup_wins().

Note that we already have some Orion5x converted to DT, and that use
PCI: board-rd88f5182.c is an example. So we could very well take Jamie
patches as-is, and move later to a DT-representation for PCI/PCIe.

Best regards,

Thomas
-- 
Thomas Petazzoni, CTO, Free Electrons
Embedded Linux, Kernel and Android engineering
http://free-electrons.com