Subject: Re: linux-next: manual merge of the char-misc tree with the drm-tegra tree

From: Stephen Rothwell <[email-masked]>
Date: Fri, 5 Nov 2021 12:52:20 +1100

Hi all,

On Wed, 27 Oct 2021 15:37:39 +1100 Stephen Rothwell <[email-masked]> wrote:
> 
> Today's linux-next merge of the char-misc tree got a conflict in:
> 
>   drivers/gpu/drm/tegra/gem.c
> 
> between commit:
> 
>   1c4d17a5267b ("drm/tegra: Implement correct DMA-BUF semantics")
> 
> from the drm-tegra tree and commit:
> 
>   16b0314aa746 ("dma-buf: move dma-buf symbols into the DMA_BUF module namespace")
> 
> from the char-misc tree.
> 
> I fixed it up (see below) and can carry the fix as necessary. This
> is now fixed as far as linux-next is concerned, but any non trivial
> conflicts should be mentioned to your upstream maintainer when your tree
> is submitted for merging.  You may also want to consider cooperating
> with the maintainer of the conflicting tree to minimise any particularly
> complex conflicts.
> 
> -- 
> Cheers,
> Stephen Rothwell
> 
> diff --cc drivers/gpu/drm/tegra/gem.c
> index 62fc7e8429d4,d38fd7e12b57..000000000000
> --- a/drivers/gpu/drm/tegra/gem.c
> +++ b/drivers/gpu/drm/tegra/gem.c
> @@@ -20,78 -21,60 +21,80 @@@
>   #include "drm.h"
>   #include "gem.h"
>   
> + MODULE_IMPORT_NS(DMA_BUF);
> + 
>  -static void tegra_bo_put(struct host1x_bo *bo)
>  +static unsigned int sg_dma_count_chunks(struct scatterlist *sgl, unsigned int nents)
>   {
>  -	struct tegra_bo *obj = host1x_to_tegra_bo(bo);
>  +	dma_addr_t next = ~(dma_addr_t)0;
>  +	unsigned int count = 0, i;
>  +	struct scatterlist *s;
>  +
>  +	for_each_sg(sgl, s, nents, i) {
>  +		/* sg_dma_address(s) is only valid for entries that have sg_dma_len(s) != 0. */
>  +		if (!sg_dma_len(s))
>  +			continue;
>  +
>  +		if (sg_dma_address(s) != next) {
>  +			next = sg_dma_address(s) + sg_dma_len(s);
>  +			count++;
>  +		}
>  +	}
>   
>  -	drm_gem_object_put(&obj->gem);
>  +	return count;
>   }
>   
>  -/* XXX move this into lib/scatterlist.c? */
>  -static int sg_alloc_table_from_sg(struct sg_table *sgt, struct scatterlist *sg,
>  -				  unsigned int nents, gfp_t gfp_mask)
>  +static inline unsigned int sgt_dma_count_chunks(struct sg_table *sgt)
>   {
>  -	struct scatterlist *dst;
>  -	unsigned int i;
>  -	int err;
>  -
>  -	err = sg_alloc_table(sgt, nents, gfp_mask);
>  -	if (err < 0)
>  -		return err;
>  -
>  -	dst = sgt->sgl;
>  +	return sg_dma_count_chunks(sgt->sgl, sgt->nents);
>  +}
>   
>  -	for (i = 0; i < nents; i++) {
>  -		sg_set_page(dst, sg_page(sg), sg->length, 0);
>  -		dst = sg_next(dst);
>  -		sg = sg_next(sg);
>  -	}
>  +static void tegra_bo_put(struct host1x_bo *bo)
>  +{
>  +	struct tegra_bo *obj = host1x_to_tegra_bo(bo);
>   
>  -	return 0;
>  +	drm_gem_object_put(&obj->gem);
>   }
>   
>  -static struct sg_table *tegra_bo_pin(struct device *dev, struct host1x_bo *bo,
>  -				     dma_addr_t *phys)
>  +static struct host1x_bo_mapping *tegra_bo_pin(struct device *dev, struct host1x_bo *bo,
>  +					      enum dma_data_direction direction)
>   {
>   	struct tegra_bo *obj = host1x_to_tegra_bo(bo);
>  -	struct sg_table *sgt;
>  +	struct drm_gem_object *gem = &obj->gem;
>  +	struct host1x_bo_mapping *map;
>   	int err;
>   
>  +	map = kzalloc(sizeof(*map), GFP_KERNEL);
>  +	if (!map)
>  +		return ERR_PTR(-ENOMEM);
>  +
>  +	kref_init(&map->ref);
>  +	map->bo = host1x_bo_get(bo);
>  +	map->direction = direction;
>  +	map->dev = dev;
>  +
>   	/*
>  -	 * If we've manually mapped the buffer object through the IOMMU, make
>  -	 * sure to return the IOVA address of our mapping.
>  -	 *
>  -	 * Similarly, for buffers that have been allocated by the DMA API the
>  -	 * physical address can be used for devices that are not attached to
>  -	 * an IOMMU. For these devices, callers must pass a valid pointer via
>  -	 * the @phys argument.
>  -	 *
>  -	 * Imported buffers were also already mapped at import time, so the
>  -	 * existing mapping can be reused.
>  +	 * Imported buffers need special treatment to satisfy the semantics of DMA-BUF.
>   	 */
>  -	if (phys) {
>  -		*phys = obj->iova;
>  -		return NULL;
>  +	if (gem->import_attach) {
>  +		struct dma_buf *buf = gem->import_attach->dmabuf;
>  +
>  +		map->attach = dma_buf_attach(buf, dev);
>  +		if (IS_ERR(map->attach)) {
>  +			err = PTR_ERR(map->attach);
>  +			goto free;
>  +		}
>  +
>  +		map->sgt = dma_buf_map_attachment(map->attach, direction);
>  +		if (IS_ERR(map->sgt)) {
>  +			dma_buf_detach(buf, map->attach);
>  +			err = PTR_ERR(map->sgt);
>  +			goto free;
>  +		}
>  +
>  +		err = sgt_dma_count_chunks(map->sgt);
>  +		map->size = gem->size;
>  +
>  +		goto out;
>   	}
>   
>   	/*

This is now a conflict between the drm-tegra tree and Linus' tree.

-- 
Cheers,
Stephen Rothwell