Re: [PATCH] video: fbdev: atyfb: only use ioremap_uc() on i386 and ia64

[Christoph Hellwig <hch@xxxxxx>]

On Tue, Nov 12, 2019 at 02:04:16PM +0100, Daniel Vetter wrote:
> Wut ... Maybe I'm missing something, but from how we use mtrr in other
> gpu drivers it's a) either you use MTRR because that's all you got or
> b) you use pat. Mixing both sounds like a pretty bad idea, since if
> you need MTRR for performance (because you dont have PAT) then you
> can't fix the wc with the PAT-based ioremap_uc. And if you have PAT,
> then you don't really need an MTRR to get wc.
> 
> So I'd revert this patch from Luis and ...

Sounds great to me..

> ... apply this one. Since the same reasoning should apply to anything
> that's running on any cpu with PAT.

Can you take a look at "mfd: intel-lpss: Use devm_ioremap_uc for MMIO"
in linux-next, which also looks rather fishy to me?  Can't we use
the MTRR APIs to override the broken BIOS MTRR setup there as well?

With that we could kill ioremap_uc entirely.