linux-kernel - Re: [PATCH] fbdev: suppress warning when assigning vga-save/restore base

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Date:	Mon, 05 Aug 2013 14:14:05 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Ondrej Zajicek <santiago@...reenet.org>
CC:	David Miller <davem@...emloft.net>, dh.herrmann@...il.com,
	linux-fbdev@...r.kernel.org, linux-kernel@...r.kernel.org,
	plagnioj@...osoft.com, tomi.valkeinen@...com,
	Ondrej Zary <linux@...nbow-software.org>
Subject: Re: [PATCH] fbdev: suppress warning when assigning vga-save/restore
 base

On 08/05/2013 02:02 PM, H. Peter Anvin wrote:
> On 08/05/2013 01:29 PM, Ondrej Zajicek wrote:
>>
>> How this could even work? AFAIK these cards have to be explicitly programmed
>> to enable MMIO (which was not done in the patches). These patches claim that
>> it is for multi-domain PCI. I would guess that vgabase is NULL in common
>> configurations but if it is non-NULL, it probably wouldn't work, unless
>> there is some hardware magic that transparently converts MMIO (from CPU PoV)
>> to port IO (from card/PCI PoV).
>>
> 
> They presumably use iowrite/ioread, which use either I/O instructions or
> memory instructions depending on the address.
> 

So the confusion really is in the iowrite interface, which can take
either a physical port address or a virtual memory address...

	-hpa


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