fix(ufs): only allow using one slot

Currently the UFS driver places the Command UPIU, Response UPIU, and
PRDT immediately after the UTP Transfer Request Descriptor. This space
would normally be reserved for other slots in the UTP Transfer Request
List, but because we always use slot zero, the other slots in the UTP
Transfer Request List are never used and this is okay.

Because the Command UPIU, Response UPIU, and PRDT are placed inside the
UTP Transfer Request List, the UFS driver would break if two or more
slots were used at the same time. Therefore, in a sense the
get_empty_slot() function is misleading. It gives developers the
illusion that they can use two or more slots simultaneously but in
reality they cannot.

This change deletes the get_empty_slot() function and replaces it with
is_slot_available() so that only one slot can be used.

Signed-off-by: Jorge Troncoso <jatron@google.com>
Change-Id: I57f316640a1cdd56493505ede61f3012ceb2f305

diff --git a/drivers/ufs/ufs.c b/drivers/ufs/ufs.c
index cf3f0e62ceaf08593521259347d3cf75c8863323..d6c893d3a997894e470d1ce18553339772286273 100644 (file)
--- a/drivers/ufs/ufs.c
+++ b/drivers/ufs/ufs.c
@@ -234,42 +234,33 @@ static int ufshc_link_startup(uintptr_t base)
        return -EIO;
 }
 
-/* Check Door Bell register to get an empty slot */
-static int get_empty_slot(int *slot)
+/* Read Door Bell register to check if slot zero is available */
+static int is_slot_available(void)
 {
-       unsigned int data;
-       int i;
-
-       data = mmio_read_32(ufs_params.reg_base + UTRLDBR);
-       for (i = 0; i < nutrs; i++) {
-               if ((data & 1) == 0)
-                       break;
-               data = data >> 1;
-       }
-       if (i >= nutrs)
+       if (mmio_read_32(ufs_params.reg_base + UTRLDBR) & 0x1) {
                return -EBUSY;
-       *slot = i;
+       }
        return 0;
 }
 
 static void get_utrd(utp_utrd_t *utrd)
 {
        uintptr_t base;
-       int slot = 0, result;
+       int result;
        utrd_header_t *hd;
 
        assert(utrd != NULL);
-       result = get_empty_slot(&slot);
+       result = is_slot_available();
        assert(result == 0);
 
        /* clear utrd */
        memset((void *)utrd, 0, sizeof(utp_utrd_t));
-       base = ufs_params.desc_base + (slot * sizeof(utrd_header_t));
+       base = ufs_params.desc_base;
        /* clear the descriptor */
        memset((void *)base, 0, UFS_DESC_SIZE);
 
        utrd->header = base;
-       utrd->task_tag = slot + 1;
+       utrd->task_tag = 1; /* We always use the first slot */
        /* CDB address should be aligned with 128 bytes */
        utrd->upiu = ALIGN_CDB(utrd->header + sizeof(utrd_header_t));
        utrd->resp_upiu = ALIGN_8(utrd->upiu + sizeof(cmd_upiu_t));