linux-kernel - Re: [PATCH 3/4] drm/nouveau: stop using is_swiotlb

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Date:   Thu, 18 May 2023 16:30:49 -0400
From:   Lyude Paul <lyude@...hat.com>
To:     Christoph Hellwig <hch@....de>, Juergen Gross <jgross@...e.com>,
        Stefano Stabellini <sstabellini@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
        "H. Peter Anvin" <hpa@...or.com>, Ben Skeggs <bskeggs@...hat.com>,
        Karol Herbst <kherbst@...hat.com>
Cc:     xen-devel@...ts.xenproject.org, iommu@...ts.linux.dev,
        linux-kernel@...r.kernel.org, nouveau@...ts.freedesktop.org
Subject: Re: [PATCH 3/4] drm/nouveau: stop using is_swiotlb_active

Reviewed-by: Lyude Paul <lyude@...hat.com>

Thanks for getting to this!

On Thu, 2023-05-18 at 15:42 +0200, Christoph Hellwig wrote:
> Drivers have no business looking into dma-mapping internals and check
> what backend is used.  Unfortunstely the DRM core is still broken and
> tries to do plain page allocations instead of using DMA API allocators
> by default and uses various bandaids on when to use dma_alloc_coherent.
> 
> Switch nouveau to use the same (broken) scheme as amdgpu and radeon
> to remove the last driver user of is_swiotlb_active.
> 
> Signed-off-by: Christoph Hellwig <hch@....de>
> ---
>  drivers/gpu/drm/nouveau/nouveau_ttm.c | 10 +++-------
>  1 file changed, 3 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/gpu/drm/nouveau/nouveau_ttm.c b/drivers/gpu/drm/nouveau/nouveau_ttm.c
> index 1469a88910e45d..486f39f31a38df 100644
> --- a/drivers/gpu/drm/nouveau/nouveau_ttm.c
> +++ b/drivers/gpu/drm/nouveau/nouveau_ttm.c
> @@ -24,9 +24,9 @@
>   */
>  
>  #include <linux/limits.h>
> -#include <linux/swiotlb.h>
>  
>  #include <drm/ttm/ttm_range_manager.h>
> +#include <drm/drm_cache.h>
>  
>  #include "nouveau_drv.h"
>  #include "nouveau_gem.h"
> @@ -265,7 +265,6 @@ nouveau_ttm_init(struct nouveau_drm *drm)
>  	struct nvkm_pci *pci = device->pci;
>  	struct nvif_mmu *mmu = &drm->client.mmu;
>  	struct drm_device *dev = drm->dev;
> -	bool need_swiotlb = false;
>  	int typei, ret;
>  
>  	ret = nouveau_ttm_init_host(drm, 0);
> @@ -300,13 +299,10 @@ nouveau_ttm_init(struct nouveau_drm *drm)
>  		drm->agp.cma = pci->agp.cma;
>  	}
>  
> -#if IS_ENABLED(CONFIG_SWIOTLB) && IS_ENABLED(CONFIG_X86)
> -	need_swiotlb = is_swiotlb_active(dev->dev);
> -#endif
> -
>  	ret = ttm_device_init(&drm->ttm.bdev, &nouveau_bo_driver, drm->dev->dev,
>  				  dev->anon_inode->i_mapping,
> -				  dev->vma_offset_manager, need_swiotlb,
> +				  dev->vma_offset_manager,
> +				  drm_need_swiotlb(drm->client.mmu.dmabits),
>  				  drm->client.mmu.dmabits <= 32);
>  	if (ret) {
>  		NV_ERROR(drm, "error initialising bo driver, %d\n", ret);

-- 
Cheers,
 Lyude Paul (she/her)
 Software Engineer at Red Hat