Re: [PATCH 2/6] drm: Implement drm_need_swiotlb() in drm_cache.c

[Daniel Vetter <daniel@ffwll.ch>]

On Tue, Jan 12, 2021 at 09:10:31AM +0100, Thomas Zimmermann wrote:
> The function is declared in drm_cache.h. I also removed the curly
> braces from the for loop to adhere to kernel coding style.
> 
> Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>

s/implement in/move to/ in the subject. Also would be nice to add
kerneldoc while moving (there's not kerneldoc for drm_memory) to avoid the
new warning. With that fixed:

Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>

It's mildly confusing, but in a way drm_cache.c is our "hack around
dma-api layering issues" pile, so fits :-) Maybe we should even make this
the official DOC: kerneldoc intro section for this file ...

Cheers, Daniel

> ---
>  drivers/gpu/drm/drm_cache.c  | 32 ++++++++++++++++++++++++++++++++
>  drivers/gpu/drm/drm_memory.c | 33 ---------------------------------
>  2 files changed, 32 insertions(+), 33 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_cache.c b/drivers/gpu/drm/drm_cache.c
> index 0fe3c496002a..49551a7fa22f 100644
> --- a/drivers/gpu/drm/drm_cache.c
> +++ b/drivers/gpu/drm/drm_cache.c
> @@ -30,6 +30,7 @@
>  
>  #include <linux/export.h>
>  #include <linux/highmem.h>
> +#include <xen/xen.h>
>  
>  #include <drm/drm_cache.h>
>  
> @@ -176,3 +177,34 @@ drm_clflush_virt_range(void *addr, unsigned long length)
>  #endif
>  }
>  EXPORT_SYMBOL(drm_clflush_virt_range);
> +
> +bool drm_need_swiotlb(int dma_bits)
> +{
> +	struct resource *tmp;
> +	resource_size_t max_iomem = 0;
> +
> +	/*
> +	 * Xen paravirtual hosts require swiotlb regardless of requested dma
> +	 * transfer size.
> +	 *
> +	 * NOTE: Really, what it requires is use of the dma_alloc_coherent
> +	 *       allocator used in ttm_dma_populate() instead of
> +	 *       ttm_populate_and_map_pages(), which bounce buffers so much in
> +	 *       Xen it leads to swiotlb buffer exhaustion.
> +	 */
> +	if (xen_pv_domain())
> +		return true;
> +
> +	/*
> +	 * Enforce dma_alloc_coherent when memory encryption is active as well
> +	 * for the same reasons as for Xen paravirtual hosts.
> +	 */
> +	if (mem_encrypt_active())
> +		return true;
> +
> +	for (tmp = iomem_resource.child; tmp; tmp = tmp->sibling)
> +		max_iomem = max(max_iomem,  tmp->end);
> +
> +	return max_iomem > ((u64)1 << dma_bits);
> +}
> +EXPORT_SYMBOL(drm_need_swiotlb);
> diff --git a/drivers/gpu/drm/drm_memory.c b/drivers/gpu/drm/drm_memory.c
> index f4f2bffdd5bd..e4f20a2eb6e7 100644
> --- a/drivers/gpu/drm/drm_memory.c
> +++ b/drivers/gpu/drm/drm_memory.c
> @@ -37,7 +37,6 @@
>  #include <linux/highmem.h>
>  #include <linux/pci.h>
>  #include <linux/vmalloc.h>
> -#include <xen/xen.h>
>  
>  #include <drm/drm_agpsupport.h>
>  #include <drm/drm_cache.h>
> @@ -138,35 +137,3 @@ void drm_legacy_ioremapfree(struct drm_local_map *map, struct drm_device *dev)
>  		iounmap(map->handle);
>  }
>  EXPORT_SYMBOL(drm_legacy_ioremapfree);
> -
> -bool drm_need_swiotlb(int dma_bits)
> -{
> -	struct resource *tmp;
> -	resource_size_t max_iomem = 0;
> -
> -	/*
> -	 * Xen paravirtual hosts require swiotlb regardless of requested dma
> -	 * transfer size.
> -	 *
> -	 * NOTE: Really, what it requires is use of the dma_alloc_coherent
> -	 *       allocator used in ttm_dma_populate() instead of
> -	 *       ttm_populate_and_map_pages(), which bounce buffers so much in
> -	 *       Xen it leads to swiotlb buffer exhaustion.
> -	 */
> -	if (xen_pv_domain())
> -		return true;
> -
> -	/*
> -	 * Enforce dma_alloc_coherent when memory encryption is active as well
> -	 * for the same reasons as for Xen paravirtual hosts.
> -	 */
> -	if (mem_encrypt_active())
> -		return true;
> -
> -	for (tmp = iomem_resource.child; tmp; tmp = tmp->sibling) {
> -		max_iomem = max(max_iomem,  tmp->end);
> -	}
> -
> -	return max_iomem > ((u64)1 << dma_bits);
> -}
> -EXPORT_SYMBOL(drm_need_swiotlb);
> -- 
> 2.29.2
> 

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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