This allows access to pages allocated through the driver with optional
IOMMU mapping.

v2: Fix number of bytes copied and add write method
v3: drop check for kmap return

Original-by: Christian K├Ânig <christian.koe...@amd.com>
Signed-off-by: Tom St Denis <tom.stde...@amd.com>
---
 drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c | 102 +++++++++++++++++++++++++-------
 1 file changed, 81 insertions(+), 21 deletions(-)

diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c 
b/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c
index b372d8d650a5..1338c908056f 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c
@@ -1929,38 +1929,98 @@ static const struct file_operations amdgpu_ttm_gtt_fops 
= {
 
 #endif
 
-static ssize_t amdgpu_iova_to_phys_read(struct file *f, char __user *buf,
-                                  size_t size, loff_t *pos)
+static ssize_t amdgpu_iomem_read(struct file *f, char __user *buf,
+                                size_t size, loff_t *pos)
 {
        struct amdgpu_device *adev = file_inode(f)->i_private;
-       int r;
-       uint64_t phys;
        struct iommu_domain *dom;
+       ssize_t result = 0;
+       int r;
 
-       // always return 8 bytes
-       if (size != 8)
-               return -EINVAL;
+       dom = iommu_get_domain_for_dev(adev->dev);
 
-       // only accept page addresses
-       if (*pos & 0xFFF)
-               return -EINVAL;
+       while (size) {
+               phys_addr_t addr = *pos & PAGE_MASK;
+               loff_t off = *pos & ~PAGE_MASK;
+               size_t bytes = PAGE_SIZE - off;
+               unsigned long pfn;
+               struct page *p;
+               void *ptr;
+
+               bytes = bytes < size ? bytes : size;
+
+               addr = dom ? iommu_iova_to_phys(dom, addr) : addr;
+
+               pfn = addr >> PAGE_SHIFT;
+               if (!pfn_valid(pfn))
+                       return -EPERM;
+
+               p = pfn_to_page(pfn);
+               if (p->mapping != adev->mman.bdev.dev_mapping)
+                       return -EPERM;
+
+               ptr = kmap(p);
+               r = copy_to_user(buf, ptr, bytes);
+               kunmap(p);
+               if (r)
+                       return -EFAULT;
+
+               size -= bytes;
+               *pos += bytes;
+               result += bytes;
+       }
+
+       return result;
+}
+
+static ssize_t amdgpu_iomem_write(struct file *f, const char __user *buf,
+                                size_t size, loff_t *pos)
+{
+       struct amdgpu_device *adev = file_inode(f)->i_private;
+       struct iommu_domain *dom;
+       ssize_t result = 0;
+       int r;
 
        dom = iommu_get_domain_for_dev(adev->dev);
-       if (dom)
-               phys = iommu_iova_to_phys(dom, *pos);
-       else
-               phys = *pos;
 
-       r = copy_to_user(buf, &phys, 8);
-       if (r)
-               return -EFAULT;
+       while (size) {
+               phys_addr_t addr = *pos & PAGE_MASK;
+               loff_t off = *pos & ~PAGE_MASK;
+               size_t bytes = PAGE_SIZE - off;
+               unsigned long pfn;
+               struct page *p;
+               void *ptr;
+
+               bytes = bytes < size ? bytes : size;
 
-       return 8;
+               addr = dom ? iommu_iova_to_phys(dom, addr) : addr;
+
+               pfn = addr >> PAGE_SHIFT;
+               if (!pfn_valid(pfn))
+                       return -EPERM;
+
+               p = pfn_to_page(pfn);
+               if (p->mapping != adev->mman.bdev.dev_mapping)
+                       return -EPERM;
+
+               ptr = kmap(p);
+               r = copy_from_user(ptr, buf, bytes);
+               kunmap(p);
+               if (r)
+                       return -EFAULT;
+
+               size -= bytes;
+               *pos += bytes;
+               result += bytes;
+       }
+
+       return result;
 }
 
-static const struct file_operations amdgpu_ttm_iova_fops = {
+static const struct file_operations amdgpu_ttm_iomem_fops = {
        .owner = THIS_MODULE,
-       .read = amdgpu_iova_to_phys_read,
+       .read = amdgpu_iomem_read,
+       .write = amdgpu_iomem_write,
        .llseek = default_llseek
 };
 
@@ -1973,7 +2033,7 @@ static const struct {
 #ifdef CONFIG_DRM_AMDGPU_GART_DEBUGFS
        { "amdgpu_gtt", &amdgpu_ttm_gtt_fops, TTM_PL_TT },
 #endif
-       { "amdgpu_iova", &amdgpu_ttm_iova_fops, TTM_PL_SYSTEM },
+       { "amdgpu_iomem", &amdgpu_ttm_iomem_fops, TTM_PL_SYSTEM },
 };
 
 #endif
-- 
2.14.3

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