linux-kernel - Re: ehci-hcd affects hda speed

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Date:	Tue, 18 Mar 2008 02:23:57 +0100
From:	Rene Herman <rene.herman@...access.nl>
To:	David Brownell <david-b@...bell.net>
CC:	"Lev A. Melnikovsky" <melnikovsky@...l.ru>,
	Alessandro Suardi <alessandro.suardi@...il.com>,
	Linux Kernel <linux-kernel@...r.kernel.org>
Subject: Re: ehci-hcd affects hda speed

On 18-03-08 01:00, David Brownell wrote:

> On Monday 17 March 2008, Rene Herman wrote:
>> +       case PCI_VENDOR_ID_VIA:
>> +               if (pdev->device == 0x3104 && pdev->revision >= 0x60) {
> 
> Unless you have specific docs from VIA saying that this register
> isn't revision-specific (at least in the sense that all revisions
> after 0x60 define that bit in that way), this should probably be a
> switch on pdev->revision and just include the known-safe revisions.

I'm looking at a VIA datasheet which says the revision ID for the "VT6212 / 
VT6212L PCI USB2.0 Controller" is simply 0x60. The VT61212L I myself owned 
advertised a revision ID of 0x63 and Lev's VT6212L advertises 0x65.

The thing is -- you don't necesarily immediately notice this problem. I 
noticed it earlier on an old system, as did Lev, but even if on a modern 
system you may not immediately see an IDE throughput drop, you may still 
have a sucky system.

With 0x60 documented and 0x63 and 0x65 confirmed as VT6212L, I'd personally 
still go with >= 0x60 and assume either backwards-compatibility or a "don't 
care" definition if some later revision were to not define this hack.

> At one point I had a table mapping those revision codes to
> specific VIA chips.  Too bad I didn't keep it.  ISTR that the
> VT6212 has a newer revision code than the vt8235 southbridge,
> and probably not as new as the vt8237 one...

Some googling seems to indicate that:

VT6202 = 0x5x (0x50, 0x51 at least)
VT6212 = 0x6x (0x60, 0x61, 0x63, 0x65 at least)
VT8235 = 0x82
VT8237 = 0x86
VT*800 = 0x90 (KM800Pro, VN800, K8N800, ...)

Do you want one with 0x6x? I feel it's very likely that everyone on anything 
later will then still have a sucky system. Tons of people with VT8235/VT8237 
around (although not me). Any quick test available for them?

> But otherwise, yes -- that's the kind of patch I'd sign off on
> after making this comment a bit more informative about how
> that 1 usec sleep time creates an amount of PCI bus hogging.

Version with 0x6x and the somewhat more expansive comment. I'd like to be 
able to test VT8235/VT8237 first though...

Still totally untested ofcourse.

Rene

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