libata-core: Document some limits/assumptions about ID_ATA

Signed-off-by: Alan Cox <alan@redhat.com>
Signed-off-by: Jeff Garzik <jeff@garzik.org>

1 files changed, 8 insertions, 2 deletions

diff --git a/drivers/ata/libata-core.c b/drivers/ata/libata-core.c
index 75ccf46972d8..d2141a04fff1 100644
--- a/drivers/ata/libata-core.c
+++ b/drivers/ata/libata-core.c
@@ -1618,6 +1618,9 @@ static u32 ata_pio_mask_no_iordy(const struct ata_device *adev)
  *      devices.  This function also issues ATA_CMD_INIT_DEV_PARAMS
  *      for pre-ATA4 drives.
  *
+ *      FIXME: ATA_CMD_ID_ATA is optional for early drives and right
+ *      now we abort if we hit that case. 
+ *
  *      LOCKING:
  *      Kernel thread context (may sleep)
  *
@@ -1745,10 +1748,13 @@ int ata_dev_read_id(struct ata_device *dev, unsigned int *p_class,
                 /*
                  * The exact sequence expected by certain pre-ATA4 drives is:
                  * SRST RESET
-                 * IDENTIFY
-                 * INITIALIZE DEVICE PARAMETERS
+                 * IDENTIFY (optional in early ATA)
+                 * INITIALIZE DEVICE PARAMETERS (later IDE and ATA)
                  * anything else..
                  * Some drives were very specific about that exact sequence.
+                 *
+                 * Note that ATA4 says lba is mandatory so the second check
+                 * shoud never trigger.
                  */
                 if (ata_id_major_version(id) < 4 || !ata_id_has_lba(id)) {
                         err_mask = ata_dev_init_params(dev, id[3], id[6]);