Re: [PATCH] fbdev: suppress warning when assigningvga-save/restore base

From: David Miller
Date: Mon Aug 05 2013 - 18:29:30 EST

From: Ondrej Zajicek <santiago@xxxxxxxxxxxxx>
Date: Mon, 5 Aug 2013 22:29:55 +0200

> On Sun, Aug 04, 2013 at 06:51:46PM -0700, David Miller wrote:
>> From: "H. Peter Anvin" <hpa@xxxxxxxxx>
>> Date: Sun, 04 Aug 2013 10:33:46 -0700
>> > Anyone who can dig backwards and summarize? In other words:
>> >
>> > Where in the current code do we stuff a physical address in a pointer,
>> > or a virtual address into a non-pointer?
>> The VGA register accessors try to accomodate iomem and ioport
>> accesses.
>> If they are given a non-NULL iomem pointer 'regbase' they use
>> iomem accesses, otherwise they do direct ISA port poking.
>> And yes the drivers in question are making some brash assumptions.
>> I suspect they should be using ioremap() or similar.
> Well, these drivers were written without MMIO (port IO only with NULL
> instead of 'vgabase' for VGA register accessors). They were converted in
> patches 94c322c30bd14ae6cdd369cb4a1f94c5c3809ac9,
> f8645933513c65ac55f23c63b2649097289795c6 and a few others (from David
> Miller) to potentially use MMIO by using 'vgabase' instead of NULL:
> pcibios_bus_to_resource(dev, &vga_res, &bus_reg);
> par->state.vgabase = (void __iomem *) vga_res.start;
> 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).
> Note that there are some later patches (86c0f043a737dadf034a4e6f29aefb074f4a1146)
> from Ondrej Zary that independently enable MMIO, but they use par->mmio
> field instead of par->state.vgabase .

Ok, so the correct fix would be to make them pass NULL again and to simply
ignore the resources.
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