linux-kernel - Re: [PATCH 3/3] arch/tile: tilegx PCI root complex support

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Message-ID: <4F8356C7.60706@tilera.com>
Date:	Mon, 9 Apr 2012 17:38:15 -0400
From:	Chris Metcalf <cmetcalf@...era.com>
To:	Arnd Bergmann <arnd@...db.de>
CC:	<linux-kernel@...r.kernel.org>, <linux-pci@...r.kernel.org>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	Jesse Barnes <jbarnes@...tuousgeek.org>,
	"Michael S. Tsirkin" <mst@...hat.com>,
	Myron Stowe <myron.stowe@...hat.com>,
	Jiri Kosina <jkosina@...e.cz>, Joe Perches <joe@...ches.com>,
	David Howells <dhowells@...hat.com>
Subject: Re: [PATCH 3/3] arch/tile: tilegx PCI root complex support

On 4/9/2012 9:59 AM, Arnd Bergmann wrote:
> On Saturday 07 April 2012, Chris Metcalf wrote:
>> This change implements PCIe root complex support for tilegx using
>> the kernel support layer for accessing the TRIO hardware shim.
>>
>> Signed-off-by: Chris Metcalf <cmetcalf@...era.com>
> Hi Chris,
>
> I don't know if we discussed it during the initial merge, but I notice that the PIO
> accessors (inb/outb and friends) are still not implemented in this patch. Normally
> PIO can just be mapped into the MMIO address space, so that inb() becomes
> a call to readb() with an offset on the address.

I asked our PCI expert here, who said, "My understanding is that if someone
wants to use inb/outb to access MMIO space, he'll get the MMIO, as opposed
to methods implemented with I/O instructions which are not supported by
TILE.  If the driver is dependent on the I/O instructions, it won't work on
TILE. These drivers are legacy PC drivers, e.g. ATA devices, which are not
supported by TILE."

Should we just arrange to #include <asm-generic/io.h> to pick up inb/outb
et al?  Any reason to think a non-zero offset should be part of the
solution?  (I don't really understand how inb/outb are used by modern drivers.)

> Using mdelay is generally considered very rude. Since you are not in
> atomic context here, just use msleep() instead.

Done.

Thanks for all your reviews!

-- 
Chris Metcalf, Tilera Corp.
http://www.tilera.com

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