linux-kernel - Re: RFC: outb 0x80 in inb_p, outb_p harmful on some modern AMD64 with MCP51 laptops

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Message-ID: <20071214143328.GB10130@elte.hu>
Date:	Fri, 14 Dec 2007 15:33:28 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Alan Cox <alan@...rguk.ukuu.org.uk>
Cc:	unlisted-recipients: no@...is.elte.hu, To-header@...is.elte.hu,
	on@...is.elte.hu, "input <"@elvis.elte.hu, ;
	Rene Herman <rene.herman@...access.nl>,
	Paul Rolland <rol@...917.net>,
	"H. Peter Anvin" <hpa@...or.com>, Krzysztof Halasa <khc@...waw.pl>,
	Pavel Machek <pavel@....cz>, Andi Kleen <andi@...stfloor.org>,
	linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>, rol@...be.net
Subject: Re: RFC: outb 0x80 in inb_p, outb_p harmful on some modern AMD64
	with MCP51 laptops


* Alan Cox <alan@...rguk.ukuu.org.uk> wrote:

> There is another reason we can't just do a dumb changeover - two 
> actually
> 
> #1: Some drivers are using inb_p/outb_p in PCI cases which are going 
> #to cause PCI posting changes. Most are probably just wrong in the 
> #first place but they need hand checking

hm, any intelligent way to force PCI posting? I guess not.

here's a list of candidate drivers (match the out*_p() pattern and do 
pci)

./char/epca.c 
./char/sonypi.c
./scsi/megaraid.c
./ide/pci/serverworks.c
./ide/pci/cmd640.c
./input/mouse/pc110pad.c
./i2c/busses/i2c-amd756.c
./i2c/busses/i2c-ali15x3.c
./i2c/busses/i2c-ali1563.c
./i2c/busses/i2c-ali1535.c
./i2c/busses/i2c-viapro.c
./i2c/busses/i2c-nforce2.c
./i2c/busses/i2c-i801.c
./i2c/busses/i2c-piix4.c
./hwmon/vt8231.c
./hwmon/via686a.c
./hwmon/sis5595.c
./telephony/ixj.c
./net/irda/donauboe.c
./watchdog/pcwd_pci.c
./watchdog/wdt_pci.c

> #2: We've got SMP cases that only 'work' because the odds of splitting
> the outb and the following port 0x80 cycle, which locks the bus, are tiny.
> 
> That is we've got
> 
> 		CPU1			CPU2
> 		main path		irq path
> 		outb
> 					outb
> 
> 		inb 0x80
> 					inb 0x80
> 
> races in one or two spots.

which seems to suggest we are better off not doing the port 0x80 trick 
at all.

	Ingo
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