libata: Add atapi_dmadir force flag

Some device require DMADIR to be enabled, but are not detected as such
by atapi_id_dmadir.  One such example is "Asus Serillel 2"
SATA-host-to-PATA-device bridge: the bridge itself requires DMADIR,
even if the bridged device does not.

As atapi_dmadir module parameter can cause problems with some devices
(as per Tejun Heo's memory), enabling it globally may not be possible
depending on the hardware.

This patch adds atapi_dmadir in the form of a "force" horkage value,
allowing global, per-bus and per-device control.

Signed-off-by: Vincent Pelletier <plr.vincent@gmail.com>
Signed-off-by: Tejun Heo <tj@kernel.org>

1 files changed, 2 insertions, 0 deletions

diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index c3bfacb92910..489815e3e484 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -1456,6 +1456,8 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
 
                         * dump_id: dump IDENTIFY data.
 
+                        * atapi_dmadir: Enable ATAPI DMADIR bridge support
+
                         If there are multiple matching configurations changing
                         the same attribute, the last one is used.