linux-kernel - Re: [Nouveau] [PATCH v4 1/3] drm/nouveau: set streaming DMA mask early

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Date:   Thu, 6 Oct 2016 13:57:10 +0100
From:   Ard Biesheuvel <ard.biesheuvel@...aro.org>
To:     Alexandre Courbot <gnurou@...il.com>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Ben Skeggs <bskeggs@...hat.com>,
        David Airlie <airlied@...ux.ie>,
        "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
        "nouveau@...ts.freedesktop.org" <nouveau@...ts.freedesktop.org>
Subject: Re: [Nouveau] [PATCH v4 1/3] drm/nouveau: set streaming DMA mask early

On 3 October 2016 at 06:39, Alexandre Courbot <gnurou@...il.com> wrote:
> On Mon, Sep 26, 2016 at 9:32 PM, Ard Biesheuvel
> <ard.biesheuvel@...aro.org> wrote:
>> Some subdevices (i.e., fb/nv50.c and fb/gf100.c) map a scratch page using
>> dma_map_page() way before the TTM layer has had a chance to set the DMA
>> mask. This may prevent the driver from loading at all on platforms whose
>> system memory is not covered by the default DMA mask of 32-bit (i.e., when
>> all RAM is above 4 GB).
>>
>> So set a preliminary DMA mask right after constructing the PCI device, and
>> base it on the .dma_bits member of the MMU subdevice, which is what the TTM
>> layer will base the DMA mask on as well.
>>
>> Signed-off-by: Ard Biesheuvel <ard.biesheuvel@...aro.org>
>> ---
>>  drivers/gpu/drm/nouveau/nouveau_drm.c | 11 +++++++++++
>>  1 file changed, 11 insertions(+)
>>
>> diff --git a/drivers/gpu/drm/nouveau/nouveau_drm.c b/drivers/gpu/drm/nouveau/nouveau_drm.c
>> index 652ab111dd74..e61e9a0adb51 100644
>> --- a/drivers/gpu/drm/nouveau/nouveau_drm.c
>> +++ b/drivers/gpu/drm/nouveau/nouveau_drm.c
>> @@ -361,6 +361,17 @@ static int nouveau_drm_probe(struct pci_dev *pdev,
>>
>>         pci_set_master(pdev);
>>
>> +       /*
>> +        * Set a preliminary DMA mask based on the .dma_bits member of the
>> +        * MMU subdevice. This allows other subdevices to create DMA mappings
>> +        * in their init() function, which are called before the TTM layer sets
>> +        * the DMA mask definitively.
>> +        * This is necessary for platforms where the default DMA mask of 32
>> +        * does not cover any system memory, i.e., when all RAM is > 4 GB.
>> +        */
>> +       dma_set_mask_and_coherent(device->dev,
>> +                                 DMA_BIT_MASK(device->mmu->dma_bits));
>
> I would just move this to nvkm_device_pci_new() so that it perfectly
> mirrors the same call done in nvkm_device_tegra_new(), which was done
> for the same purpose. Otherwise, looks good to me.

OK, will do that.