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Date:   Wed, 3 Jun 2020 17:13:37 -0300
From:   Jason Gunthorpe <jgg@mellanox.com>
To:     Dave Airlie <airlied@gmail.com>,
        Christoph Hellwig <hch@infradead.org>,
        Christian =?utf-8?B?S8O2bmln?= <christian.koenig@amd.com>
Cc:     Linus Torvalds <torvalds@linux-foundation.org>,
        Daniel Vetter <daniel.vetter@ffwll.ch>,
        dri-devel <dri-devel@lists.freedesktop.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Logan Gunthorpe <logang@deltatee.com>
Subject: Re: [git pull] drm for 5.8-rc1
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On Tue, Jun 02, 2020 at 04:06:32PM +1000, Dave Airlie wrote:
> Hi Linus,
> 
> This is the main drm pull request for 5.8-rc1.
> 
> Highlights:
> Core DRM had a lot of refactoring around managed drm resources to make
> drivers simpler.
> Intel Tigerlake support is on by default
> amdgpu now support p2p PCI buffer sharing and encrypted GPU memory

Christoph Hellwig basically NAK'd this approach, why is it getting
merged all of a sudden??

https://lore.kernel.org/intel-gfx/20200311152838.GA24280@infradead.org/

Are we now OK with this same approach open coded in a driver?

This wasn't Cc'd to the usual people doing work in this PCI P2P area??

See

commit f44ffd677fb3562ac0a1ff9c8ae52672be741f00
Author: Christian König <christian.koenig@amd.com>
Date:   Fri Mar 23 16:56:37 2018 +0100

    drm/amdgpu: add support for exporting VRAM using DMA-buf v3
    
    We should be able to do this now after checking all the prerequisites.
    
    v2: fix entrie count in the sgt
    v3: manually construct the sg
    
    Signed-off-by: Christian König <christian.koenig@amd.com>
    Acked-by: Daniel Vetter <daniel.vetter@ffwll.ch>
    Acked-by: Sumit Semwal <sumit.semwal@linaro.org>
    Link: https://patchwork.freedesktop.org/patch/359295

[..]

diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_vram_mgr.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_vram_mgr.c
index 82a3299e53c042..128a667ed8fa0d 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_vram_mgr.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_vram_mgr.c
@@ -22,6 +22,7 @@
  * Authors: Christian König
  */
 
+#include <linux/dma-mapping.h>
 #include "amdgpu.h"
 #include "amdgpu_vm.h"
 #include "amdgpu_atomfirmware.h"
@@ -458,6 +459,104 @@ static void amdgpu_vram_mgr_del(struct ttm_mem_type_manager *man,
 	mem->mm_node = NULL;
 }
 
+/**
+ * amdgpu_vram_mgr_alloc_sgt - allocate and fill a sg table
+ *
+ * @adev: amdgpu device pointer
+ * @mem: TTM memory object
+ * @dev: the other device
+ * @dir: dma direction
+ * @sgt: resulting sg table
+ *
+ * Allocate and fill a sg table from a VRAM allocation.
+ */
+int amdgpu_vram_mgr_alloc_sgt(struct amdgpu_device *adev,
+			      struct ttm_mem_reg *mem,
+			      struct device *dev,
+			      enum dma_data_direction dir,
+			      struct sg_table **sgt)
+{
+	struct drm_mm_node *node;
+	struct scatterlist *sg;
+	int num_entries = 0;
+	unsigned int pages;
+	int i, r;
+
+	*sgt = kmalloc(sizeof(*sg), GFP_KERNEL);
+	if (!*sgt)
+		return -ENOMEM;
+
+	for (pages = mem->num_pages, node = mem->mm_node;
+	     pages; pages -= node->size, ++node)
+		++num_entries;
+
+	r = sg_alloc_table(*sgt, num_entries, GFP_KERNEL);
+	if (r)
+		goto error_free;
+
+	for_each_sg((*sgt)->sgl, sg, num_entries, i)
+		sg->length = 0;
+
+	node = mem->mm_node;
+	for_each_sg((*sgt)->sgl, sg, num_entries, i) {
+		phys_addr_t phys = (node->start << PAGE_SHIFT) +
+			adev->gmc.aper_base;
+		size_t size = node->size << PAGE_SHIFT;
+		dma_addr_t addr;
+
+		++node;
+		addr = dma_map_resource(dev, phys, size, dir,
+					DMA_ATTR_SKIP_CPU_SYNC);
+		r = dma_mapping_error(dev, addr);
+		if (r)
+			goto error_unmap;
+
+		sg_set_page(sg, NULL, size, 0);
+		sg_dma_address(sg) = addr;
+		sg_dma_len(sg) = size;
                ^^^^^^^^^^^^^^
  
Jason