dma-buf: Remove kmap kerneldoc vestiges

Also try to clarify a bit when dma_buf_begin/end_cpu_access should
be called.

Acked-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Cc: Thomas Zimmermann <tzimmermann@suse.de>
Cc: Sumit Semwal <sumit.semwal@linaro.org>
Cc: "Christian König" <christian.koenig@amd.com>
Cc: linux-media@vger.kernel.org
Cc: linaro-mm-sig@lists.linaro.org
Link: https://patchwork.freedesktop.org/patch/msgid/20201211155843.3348718-1-daniel.vetter@ffwll.ch

1 files changed, 9 insertions, 16 deletions

diff --git a/include/linux/dma-buf.h b/include/linux/dma-buf.h
index cf72699cb2bc..7eca37c8b10c 100644
--- a/include/linux/dma-buf.h
+++ b/include/linux/dma-buf.h
@@ -183,24 +183,19 @@ struct dma_buf_ops {
 	 * @begin_cpu_access:
 	 *
 	 * This is called from dma_buf_begin_cpu_access() and allows the
-	 * exporter to ensure that the memory is actually available for cpu
-	 * access - the exporter might need to allocate or swap-in and pin the
-	 * backing storage. The exporter also needs to ensure that cpu access is
-	 * coherent for the access direction. The direction can be used by the
-	 * exporter to optimize the cache flushing, i.e. access with a different
+	 * exporter to ensure that the memory is actually coherent for cpu
+	 * access. The exporter also needs to ensure that cpu access is coherent
+	 * for the access direction. The direction can be used by the exporter
+	 * to optimize the cache flushing, i.e. access with a different
 	 * direction (read instead of write) might return stale or even bogus
 	 * data (e.g. when the exporter needs to copy the data to temporary
 	 * storage).
 	 *
-	 * This callback is optional.
+	 * Note that this is both called through the DMA_BUF_IOCTL_SYNC IOCTL
+	 * command for userspace mappings established through @mmap, and also
+	 * for kernel mappings established with @vmap.
 	 *
-	 * FIXME: This is both called through the DMA_BUF_IOCTL_SYNC command
-	 * from userspace (where storage shouldn't be pinned to avoid handing
-	 * de-factor mlock rights to userspace) and for the kernel-internal
-	 * users of the various kmap interfaces, where the backing storage must
-	 * be pinned to guarantee that the atomic kmap calls can succeed. Since
-	 * there's no in-kernel users of the kmap interfaces yet this isn't a
-	 * real problem.
+	 * This callback is optional.
 	 *
 	 * Returns:
 	 *
@@ -216,9 +211,7 @@ struct dma_buf_ops {
 	 *
 	 * This is called from dma_buf_end_cpu_access() when the importer is
 	 * done accessing the CPU. The exporter can use this to flush caches and
-	 * unpin any resources pinned in @begin_cpu_access.
-	 * The result of any dma_buf kmap calls after end_cpu_access is
-	 * undefined.
+	 * undo anything else done in @begin_cpu_access.
 	 *
 	 * This callback is optional.
 	 *