linux-kernel - Re: [Nouveau] [PATCH v4 2/3] drm/nouveau/fb/gf100: defer DMA mapping of scratch page to init() hook

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Date:   Mon, 3 Oct 2016 14:44:41 +0900
From:   Alexandre Courbot <gnurou@...il.com>
To:     Ard Biesheuvel <ard.biesheuvel@...aro.org>
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 2/3] drm/nouveau/fb/gf100: defer DMA mapping
 of scratch page to init() hook

On Mon, Sep 26, 2016 at 9:32 PM, Ard Biesheuvel
<ard.biesheuvel@...aro.org> wrote:
> The 100c10 scratch page is mapped using dma_map_page() before the TTM
> layer has had a chance to set the DMA mask. This means we are still
> running with the default of 32 when this code executes, and this causes
> problems for platforms with no memory below 4 GB (such as AMD Seattle)
>
> So move the dma_map_page() to the .init hook, which executes after the
> DMA mask has been set.
>
> Signed-off-by: Ard Biesheuvel <ard.biesheuvel@...aro.org>
> ---
>  drivers/gpu/drm/nouveau/nvkm/subdev/fb/gf100.c | 26 ++++++++++++++------
>  1 file changed, 18 insertions(+), 8 deletions(-)
>
> diff --git a/drivers/gpu/drm/nouveau/nvkm/subdev/fb/gf100.c b/drivers/gpu/drm/nouveau/nvkm/subdev/fb/gf100.c
> index 76433cc66fff..5c8132873e60 100644
> --- a/drivers/gpu/drm/nouveau/nvkm/subdev/fb/gf100.c
> +++ b/drivers/gpu/drm/nouveau/nvkm/subdev/fb/gf100.c
> @@ -93,7 +93,18 @@ gf100_fb_init(struct nvkm_fb *base)
>         struct gf100_fb *fb = gf100_fb(base);
>         struct nvkm_device *device = fb->base.subdev.device;
>
> -       if (fb->r100c10_page)
> +       if (!fb->r100c10) {
> +               dma_addr_t addr = dma_map_page(device->dev, fb->r100c10_page, 0,
> +                                              PAGE_SIZE, DMA_BIDIRECTIONAL);
> +               if (!dma_mapping_error(device->dev, addr)) {
> +                       fb->r100c10 = addr;
> +               } else {
> +                       nvkm_warn(&fb->base.subdev,
> +                                "dma_map_page() failed on 100c10 page\n");
> +               }
> +       }
> +
> +       if (fb->r100c10)
>                 nvkm_wr32(device, 0x100c10, fb->r100c10 >> 8);

gf100_fb_oneinit() seems to be a better place for this, since it will
be executed exactly once, which is what you want for a memory
allocation. As you can see other memory allocations are also performed
there, which hints it should have been done there (and not in ctor) in
the first place. Maybe you can also move the alloc_page() there so
everything is done in the same place.

>  }
>
> @@ -103,12 +114,13 @@ gf100_fb_dtor(struct nvkm_fb *base)
>         struct gf100_fb *fb = gf100_fb(base);
>         struct nvkm_device *device = fb->base.subdev.device;
>
> -       if (fb->r100c10_page) {
> +       if (fb->r100c10) {
>                 dma_unmap_page(device->dev, fb->r100c10, PAGE_SIZE,
>                                DMA_BIDIRECTIONAL);
> -               __free_page(fb->r100c10_page);
>         }
>
> +       __free_page(fb->r100c10_page);
> +

If you move the allocation/mapping to gf100_fb_oneinit() then I
suppose you don't need this change.