nvme: Elaborate on cache maintenance operation in get/set_features

At the moment the nvme_get_features() and nvme_set_features() functions
carry a (somewhat misleading) comment about missing cache maintenance.

As it turns out, nvme_get_features() has no caller at all in the tree,
and nvme_set_features' only user doesn't use a DMA buffer.

Mention that in the comment, and leave some breadcrumbs for the future,
should those functions attract more users.

Signed-off-by: Andre Przywara <andre.przywara@arm.com>
Reviewed-by: Michael Trimarchi <michael@amarulasolutions.com>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>

diff --git a/drivers/nvme/nvme.c b/drivers/nvme/nvme.c
index c9efeff4bc9b331047d584f871044221471c7964..c61dab20c5f081cd766348226e3266a707542f11 100644 (file)
--- a/drivers/nvme/nvme.c
+++ b/drivers/nvme/nvme.c
@@ -489,6 +489,7 @@ int nvme_get_features(struct nvme_dev *dev, unsigned fid, unsigned nsid,
                      dma_addr_t dma_addr, u32 *result)
 {
        struct nvme_command c;
+       int ret;
 
        memset(&c, 0, sizeof(c));
        c.features.opcode = nvme_admin_get_features;
@@ -496,12 +497,20 @@ int nvme_get_features(struct nvme_dev *dev, unsigned fid, unsigned nsid,
        c.features.prp1 = cpu_to_le64(dma_addr);
        c.features.fid = cpu_to_le32(fid);
 
+       ret = nvme_submit_admin_cmd(dev, &c, result);
+
        /*
-        * TODO: add cache invalidate operation when the size of
-        * the DMA buffer is known
+        * TODO: Add some cache invalidation when a DMA buffer is involved
+        * in the request, here and before the command gets submitted. The
+        * buffer size varies by feature, also some features use a different
+        * field in the command packet to hold the buffer address.
+        * Section 5.21.1 (Set Features command) in the NVMe specification
+        * details the buffer requirements for each feature.
+        *
+        * At the moment there is no user of this function.
         */
 
-       return nvme_submit_admin_cmd(dev, &c, result);
+       return ret;
 }
 
 int nvme_set_features(struct nvme_dev *dev, unsigned fid, unsigned dword11,
@@ -516,8 +525,14 @@ int nvme_set_features(struct nvme_dev *dev, unsigned fid, unsigned dword11,
        c.features.dword11 = cpu_to_le32(dword11);
 
        /*
-        * TODO: add cache flush operation when the size of
-        * the DMA buffer is known
+        * TODO: Add a cache clean (aka flush) operation when a DMA buffer is
+        * involved in the request. The buffer size varies by feature, also
+        * some features use a different field in the command packet to hold
+        * the buffer address. Section 5.21.1 (Set Features command) in the
+        * NVMe specification details the buffer requirements for each
+        * feature.
+        * At the moment the only user of this function is not using
+        * any DMA buffer at all.
         */
 
        return nvme_submit_admin_cmd(dev, &c, result);