diff options
| -rw-r--r-- | drivers/mtd/devices/st_spi_fsm.c | 95 |
1 files changed, 79 insertions, 16 deletions
diff --git a/drivers/mtd/devices/st_spi_fsm.c b/drivers/mtd/devices/st_spi_fsm.c index 54ffe5223e64..bebc8b5637c0 100644 --- a/drivers/mtd/devices/st_spi_fsm.c +++ b/drivers/mtd/devices/st_spi_fsm.c @@ -663,6 +663,23 @@ 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(SPINOR_OP_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) | @@ -695,22 +712,6 @@ 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) { @@ -772,6 +773,68 @@ 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, 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, const uint32_t *buf, uint32_t size) { |