linux-kernel - Re: [PATCH v2 04/10] drm/nouveau/fb: add GK20A support

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Message-ID: <CAAVeFuJrs8Sv9UZg=Tj6gJeHOXj9YSX4gT1TNdrfXvVfrBHerQ@mail.gmail.com>
Date:	Thu, 1 May 2014 13:49:28 +0900
From:	Alexandre Courbot <gnurou@...il.com>
To:	Thierry Reding <thierry.reding@...il.com>
Cc:	Alexandre Courbot <acourbot@...dia.com>,
	Ben Skeggs <bskeggs@...hat.com>,
	"nouveau@...ts.freedesktop.org" <nouveau@...ts.freedesktop.org>,
	"dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
	"linux-tegra@...r.kernel.org" <linux-tegra@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 04/10] drm/nouveau/fb: add GK20A support

On Mon, Apr 28, 2014 at 8:44 PM, Thierry Reding
<thierry.reding@...il.com> wrote:
> On Wed, Apr 23, 2014 at 03:11:01PM +0900, Alexandre Courbot wrote:
>> On Wed, Apr 23, 2014 at 11:07 AM, Alexandre Courbot <acourbot@...dia.com> wrote:
>> > On 04/22/2014 07:40 PM, Thierry Reding wrote:
>> >>
>> >> * PGP Signed by an unknown key
>> >>
>> >>
>> >> On Mon, Apr 21, 2014 at 03:02:16PM +0900, Alexandre Courbot wrote:
>> >> [...]
>> >>>
>> >>> diff --git a/drivers/gpu/drm/nouveau/core/subdev/fb/ramgk20a.c
>> >>> b/drivers/gpu/drm/nouveau/core/subdev/fb/ramgk20a.c
>> >>
>> >> [...]
>> >>>
>> >>> +               pages = dma_alloc_from_contiguous(dev, ncmin, order);
>> >>> +               if (!pages) {
>> >>> +                       gk20a_ram_put(pfb, &mem);
>> >>> +                       return -ENOMEM;
>> >>> +               }
>> >>> +
>> >>> +               dma_addr = pfn_to_dma(nv_device_base(nv_device(pfb)),
>> >>> +                                     page_to_pfn(pages));
>> >>
>> >>
>> >> This breaks compilation on x86 because neither pfn_to_dma() nor
>> >> dma_to_pfn() are available. Is there some other way this can be
>> >> allocated so that these functions don't need to be called?
>> >
>> >
>> > Mmm, this is bad. There is probably another more portable way to do this.
>> > Let me look for it.
>>
>> page_to_phys()/phys_to_page() can be used by drivers and will work
>> just fine here since the CPU and GPU use the same physical addresses
>> to access memory.
>
> I'm wondering how this is going to pan out when we try adding IOMMU
> support. But I guess we can cross that bridge when we come to it.

Agreed. Besides I hope the day won't come where we have to go through
2 layers of memory translation for the GPU...
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