linux-kernel - Re: [PATCH 4/6] MTHCA driver (infiniband) use new pci interfaces

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Date:	Sun, 10 Dec 2006 22:56:26 -0700
From:	Grant Grundler <grundler@...isc-linux.org>
To:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
Cc:	Stephen Hemminger <shemminger@...l.org>,
	Greg Kroah-Hartman <gregkh@...e.de>,
	linux-pci@...ey.karlin.mff.cuni.cz, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 4/6] MTHCA driver (infiniband) use new pci interfaces

On Mon, Dec 11, 2006 at 02:55:39PM +1100, Benjamin Herrenschmidt wrote:
> On Fri, 2006-12-08 at 10:22 -0800, Stephen Hemminger wrote:
> > plain text document attachment (mthca-rbc.patch)
> > Use new pci interfaces to set read request tuning values
> > Untested because of lack of hardware.

Sorry...I missed that. I have mthca HW on publicly available IA64 machines.
I'll contact Steve off list to check if he is interested/time.

> I'm worried by this... At no point do you check the host bridge
> capabilities, and thus will happily set the max read req size to some
> value larger than the max the host bridge can cope...
> 
> I've been having exactly that problem on a number of setups, for
> example, the sky2 cards tend to start with a value of 512 while the G5's
> host bridge can't cope with more than 256 (iirc). The firmware fixes
> that up properly on the G5 at least (but not on all machines), but if
> you allow drivers to go tweak the value without a way to go check what
> are the host bridge capabilities, you are toast.
> 
> Of course, on PCI-X, this is moot, there is no clear definition on how
> to get to a host bridge config space (if any)
...
> So for PCI-X, if we want tat, we need a pcibios hook for the platform
> to validate the size requested.

Yes, agreed. 

grant
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