@@ -698,6 +698,23 @@ static struct stfsm_seq stfsm_seq_write_status = {
SEQ_CFG_STARTSEQ),
};
+/* Dummy sequence to read one byte of data from flash into the FIFO */
+static const struct stfsm_seq stfsm_seq_load_fifo_byte = {
+ .data_size = TRANSFER_SIZE(1),
+ .seq_opc[0] = (SEQ_OPC_PADS_1 |
+ SEQ_OPC_CYCLES(8) |
+ SEQ_OPC_OPCODE(FLASH_CMD_RDID)),
+ .seq = {
+ STFSM_INST_CMD1,
+ STFSM_INST_DATA_READ,
+ STFSM_INST_STOP,
+ },
+ .seq_cfg = (SEQ_CFG_PADS_1 |
+ SEQ_CFG_READNOTWRITE |
+ SEQ_CFG_CSDEASSERT |
+ SEQ_CFG_STARTSEQ),
+};
+
static int stfsm_n25q_en_32bit_addr_seq(struct stfsm_seq *seq)
{
seq->seq_opc[0] = (SEQ_OPC_PADS_1 | SEQ_OPC_CYCLES(8) |
@@ -730,22 +747,6 @@ static inline uint32_t stfsm_fifo_available(struct stfsm *fsm)
return (readl(fsm->base + SPI_FAST_SEQ_STA) >> 5) & 0x7f;
}
-static void stfsm_clear_fifo(struct stfsm *fsm)
-{
- uint32_t avail;
-
- for (;;) {
- avail = stfsm_fifo_available(fsm);
- if (!avail)
- break;
-
- while (avail) {
- readl(fsm->base + SPI_FAST_SEQ_DATA_REG);
- avail--;
- }
- }
-}
-
static inline void stfsm_load_seq(struct stfsm *fsm,
const struct stfsm_seq *seq)
{
@@ -807,6 +808,69 @@ static void stfsm_read_fifo(struct stfsm *fsm, uint32_t *buf, uint32_t size)
}
}
+/*
+ * Clear the data FIFO
+ *
+ * Typically, this is only required during driver initialisation, where no
+ * assumptions can be made regarding the state of the FIFO.
+ *
+ * The process of clearing the FIFO is complicated by fact that while it is
+ * possible for the FIFO to contain an arbitrary number of bytes [1], the
+ * SPI_FAST_SEQ_STA register only reports the number of complete 32-bit words
+ * present. Furthermore, data can only be drained from the FIFO by reading
+ * complete 32-bit words.
+ *
+ * With this in mind, a two stage process is used to the clear the FIFO:
+ *
+ * 1. Read any complete 32-bit words from the FIFO, as reported by the
+ * SPI_FAST_SEQ_STA register.
+ *
+ * 2. Mop up any remaining bytes. At this point, it is not known if there
+ * are 0, 1, 2, or 3 bytes in the FIFO. To handle all cases, a dummy FSM
+ * sequence is used to load one byte at a time, until a complete 32-bit
+ * word is formed; at most, 4 bytes will need to be loaded.
+ *
+ * [1] It is theoretically possible for the FIFO to contain an arbitrary number
+ * of bits. However, since there are no known use-cases that leave
+ * incomplete bytes in the FIFO, only words and bytes are considered here.
+ */
+static void stfsm_clear_fifo(struct stfsm *fsm)
+{
+ const struct stfsm_seq *seq = &stfsm_seq_load_fifo_byte;
+ uint32_t words;
+ int i;
+
+ /* 1. Clear any 32-bit words */
+ words = stfsm_fifo_available(fsm);
+ if (words) {
+ for (i = 0; i < words; i++)
+ readl(fsm->base + SPI_FAST_SEQ_DATA_REG);
+ dev_dbg(fsm->dev, "cleared %d words from FIFO\n", words);
+ }
+
+ /*
+ * 2. Clear any remaining bytes
+ * - Load the FIFO, one byte at a time, until a complete 32-bit word
+ * is available.
+ */
+ for (i = 0, words = 0; i < 4 && !words; i++) {
+ stfsm_load_seq(fsm, seq);
+ stfsm_wait_seq(fsm);
+ words = stfsm_fifo_available(fsm);
+ }
+
+ /* - A single word must be available now */
+ if (words != 1) {
+ dev_err(fsm->dev, "failed to clear bytes from the data FIFO\n");
+ return;
+ }
+
+ /* - Read the 32-bit word */
+ readl(fsm->base + SPI_FAST_SEQ_DATA_REG);
+
+ dev_dbg(fsm->dev, "cleared %d byte(s) from the data FIFO\n", 4 - i);
+}
+
static int stfsm_write_fifo(struct stfsm *fsm, uint32_t *buf, uint32_t size)
{
uint32_t words = size >> 2;