[PATCH 3/3] drm/i915/dmabuf: Implement pread() callback

[Janusz Krzysztofik <janusz.krzysztofik@linux.intel.com>]

We need dmabuf specific pread() callback utilizing dma-buf API,
otherwise GEM_PREAD IOCTL will no longer work with dma-buf backed
(i.e., PRIME imported) objects on hardware with no mappable aperture.

Signed-off-by: Janusz Krzysztofik <janusz.krzysztofik@linux.intel.com>
Cc: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Cc: Michal Wajdeczko <michal.wajdeczko@intel.com>
---
 drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c | 55 ++++++++++++++++++++++
 1 file changed, 55 insertions(+)

diff --git a/drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c b/drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c
index 93eea1031c82..207dbf044296 100644
--- a/drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c
+++ b/drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c
@@ -248,6 +248,60 @@ static void i915_gem_object_put_pages_dmabuf(struct drm_i915_gem_object *obj,
 				 DMA_BIDIRECTIONAL);
 }
 
+static int i915_gem_object_pread_dmabuf(struct drm_i915_gem_object *obj,
+					const struct drm_i915_gem_pread *args)
+{
+	struct dma_buf *dmabuf = obj->base.import_attach->dmabuf;
+	void __user *user_data = u64_to_user_ptr(args->data_ptr);
+	struct file *file = dmabuf->file;
+	const struct file_operations *fop = file->f_op;
+	void __force *vaddr;
+	int ret;
+
+	if (fop->read) {
+		loff_t offset = args->offset;
+
+		/*
+		 * fop->read() is supposed to call dma_buf_begin_cpu_access()
+		 * if O_SYNC flag is set, avoid calling it twice
+		 */
+		if (!(file->f_flags & O_SYNC)) {
+			ret = dma_buf_begin_cpu_access(dmabuf, DMA_FROM_DEVICE);
+			if (ret)
+				return ret;
+		}
+
+		ret = fop->read(file, user_data, args->size, &offset);
+
+		if (!(file->f_flags & O_SYNC))
+			dma_buf_end_cpu_access(dmabuf, DMA_FROM_DEVICE);
+
+		if (!ret)
+			return 0;
+	}
+
+	/* dma-buf file .read() not supported or failed, try dma_buf_vmap() */
+	ret = dma_buf_begin_cpu_access(dmabuf, DMA_FROM_DEVICE);
+	if (ret)
+		return ret;
+
+	vaddr = dma_buf_vmap(dmabuf);
+	if (!vaddr)
+		goto out_err;
+
+	ret = copy_to_user(user_data, vaddr + args->offset, args->size);
+	dma_buf_vunmap(dmabuf, vaddr);
+	if (!ret)
+		goto out_end;
+
+out_err:
+	/* fall back to GTT mapping */
+	ret = -ENODEV;
+out_end:
+	dma_buf_end_cpu_access(dmabuf, DMA_FROM_DEVICE);
+	return ret;
+}
+
 static int i915_gem_object_pwrite_dmabuf(struct drm_i915_gem_object *obj,
 					 const struct drm_i915_gem_pwrite *args)
 {
@@ -305,6 +359,7 @@ static int i915_gem_object_pwrite_dmabuf(struct drm_i915_gem_object *obj,
 static const struct drm_i915_gem_object_ops i915_gem_object_dmabuf_ops = {
 	.get_pages = i915_gem_object_get_pages_dmabuf,
 	.put_pages = i915_gem_object_put_pages_dmabuf,
+	.pread = i915_gem_object_pread_dmabuf,
 	.pwrite = i915_gem_object_pwrite_dmabuf,
 };
 
-- 
2.21.0

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