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

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Date:	Mon, 10 Dec 2007 12:02:36 +0000
From:	Alan Cox <alan@...rguk.ukuu.org.uk>
To:	Pavel Machek <pavel@....cz>
Cc:	Andi Kleen <andi@...stfloor.org>,
	"David P. Reed" <dpreed@...d.com>, linux-kernel@...r.kernel.org,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>
Subject: Re: RFC: outb 0x80 in inb_p, outb_p harmful on some modern AMD64
 with MCP51 laptops

> Really? 
> 
> udelay() seems to use
> ... cpu_data(raw_smp_processor_id()).loops_per_jiffy .. 

Ok that should be a good safety
> 
> ..so it seems that bug trap is already there... because
> raw_smp_processor_id() will probably just oops...

And I double checked my docs - they say 8 cycles - 1uS

Incidentally some of the drivers seem buggy for SMP. The bus locking
nature of the inb_p probably hid this but they don't all seem to have
sufficient locking to ensure that we don't get back to back cycles
without delays

Alan
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