linux-kernel - htpt366 PCI latency value is really high

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Date:	Thu, 26 Apr 2007 06:49:27 -0700
From:	Mike Mattie <codermattie@...il.com>
To:	Sergei Shtylyov <sshtylyov@...mvista.com>
Cc:	lkml <linux-kernel@...r.kernel.org>
Subject: htpt366 PCI latency value is really high

Hello,

while hunting down some latency problems I found something quite odd.
The latency reported by lspci -v for the HTP203N card is enormous.

00:09.0 RAID bus controller: Triones Technologies, Inc. HPT302/302N
(rev 02) Subsystem: Triones Technologies, Inc. Unknown device 0001
        Flags: bus master, 66MHz, medium devsel, latency 120, IRQ 17
        I/O ports at ec00 [size=8]
        I/O ports at e800 [size=4]
        I/O ports at e400 [size=8]
        I/O ports at e000 [size=4]
        I/O ports at dc00 [size=256]
        Expansion ROM at dffe0000 [disabled by cmd] [size=128K]
        Capabilities: [60] Power Management version 2


I am assuming that the "latency" field here is the PCI latency timer
which means this card is a bus hog. 

From some reading on this issue linux methodically sets a sane value for 
all the PCI cards it sets up, which looks normal on the rest of the system, 
which is set to the value: 32

setting the value 32 with:

setpci -v -s "00:09.0" latency_timer=32

00:09.0 RAID bus controller: Triones Technologies, Inc. HPT302/302N (rev 02)
        Subsystem: Triones Technologies, Inc. Unknown device 0001
        Flags: bus master, 66MHz, medium devsel, latency 48, IRQ 17
        I/O ports at ec00 [size=8]
        I/O ports at e800 [size=4]
        I/O ports at e400 [size=8]
        I/O ports at e000 [size=4]
        I/O ports at dc00 [size=256]
        Expansion ROM at dffe0000 [disabled by cmd] [size=128K]
        Capabilities: [60] Power Management version 2

Results in 48, which is not what I asked, but hopefully this is
linux doing the right thing.

I know this chipset is pretty brain-damaged, but is this
high latency value a work-around for broken hardware, or
just a oversight ?

Cheers,
Mike Mattie - codermattie@...il.com

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