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Re: [PATCH V2 12/16] drm/radeon: Make radeon card usable for Loongson.

To: Huacai Chen <chenhuacai@gmail.com>
Subject: Re: [PATCH V2 12/16] drm/radeon: Make radeon card usable for Loongson.
From: Lucas Stach <dev@lynxeye.de>
Date: Wed, 20 Jun 2012 08:38:13 +0200
Cc: Ralf Baechle <ralf@linux-mips.org>, linux-mips@linux-mips.org, Zhangjin Wu <wuzhangjin@gmail.com>, Hua Yan <yanh@lemote.com>, Fuxin Zhang <zhangfx@lemote.com>, dri-devel@lists.freedesktop.org, Hongliang Tao <taohl@lemote.com>, Huacai Chen <chenhc@lemote.com>
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Am Mittwoch, den 20.06.2012, 14:12 +0800 schrieb Huacai Chen:
> On Tue, Jun 19, 2012 at 3:19 PM, Lucas Stach <dev@lynxeye.de> wrote:
> > Hello Huacai,
> >
> > Am Dienstag, den 19.06.2012, 14:50 +0800 schrieb Huacai Chen:
> >> 1, Use 32-bit DMA as a workaround (Loongson has a hardware bug that it
> >>    doesn't support DMA address above 4GB).
> >
> > This is a bug of your platform/CPU and should be fixed at a lower level,
> > not in every driver. While radeon might be the only device using 40bit
> > DMA right know, it is very well possible that other devices pop up in
> > the future. So please fix your platform code to disallow >32bit DMA.
> 
> Hi, Lucas
> I have fixed my platform code to  disallow >32bit DMA. This method fix
> the DMA problems in SATA and sound card, but fails on radeon (display
> is OK, but accerlaration is unusable), because need_dma32 not only
> affect dma_mask/coherent_dma_mask, but also affect th gfp_flags of
> ttm_get_pages(). Platform code fixes cannot solve the problem of
> ttm_get_pages(), could you please give me some suggestions? Thank you.

If your platform does disallow >32bit DMA masks, radeon should already
do the right thing and set need_dma32 to true. Have a look at
radeon_device.c:783

Make sure you really disallow >32bit DMA masks, not just prefer <=32bit
masks.
> 
> >
> >> 2, Read vga bios offered by system firmware.
> >> 3, Handle io prot correctly for MIPS.
> >
> > This seems good to me, but you should really split this out in a
> > separate TTM patch.
> >
> >> 4, Don't use swiotlb on Loongson machines (when use swiotlb, GPU reset
> >>    occurs at resume from suspend).
> >>
> > While SWIOTLB might not be a common setup, simply ignoring it because it
> > doesn't work on your platform is the wrong thing to do. Could you please
> > try to root-cause the issue?
> >
[snip]



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