libata: Add the AHCI_HFLAG_NO_WRITE_TO_RO flag

While most hardware will simply ignore a write to a read-only register,
some hardware will signal an abort if this occurs.

This commit introduces the flag AHCI_HFLAG_NO_WRITE_TO_RO to prevent the
AHCI library from attempting to write to the HOST_CAP, HOST_CAP2, and
HOST_PORTS_IMPL registers which may be read-only.

Signed-off-by: Doug Berger <opendmb@gmail.com>
Signed-off-by: Tejun Heo <tj@kernel.org>

1 files changed, 2 insertions, 1 deletions

diff --git a/drivers/ata/libahci.c b/drivers/ata/libahci.c
index 4462f8a8cf2c..3e286d86ab42 100644
--- a/drivers/ata/libahci.c
+++ b/drivers/ata/libahci.c
@@ -945,7 +945,8 @@ int ahci_reset_controller(struct ata_host *host)
                 /* Some registers might be cleared on reset.  Restore
                  * initial values.
                  */
-                ahci_restore_initial_config(host);
+                if (!(hpriv->flags & AHCI_HFLAG_NO_WRITE_TO_RO))
+                        ahci_restore_initial_config(host);
         } else
                 dev_info(host->dev, "skipping global host reset\n");