Fix the issue where some flash chips like cypress S25HS256T for example return the value of the same register once a SPI transaction starts. So for example if read reg of 0x2 is requested and we start reading registers in DAC mode we start reading 4 byte aligned ie. 0x0, 0x1, 0x2 and then 0x3. In such a case the flash chip keeps returning the value of 0x0 even though we actually want the value of 0x2. STIG mode solves the above issue by not issuing a read continuosly for 4 byte aligned data.
Signed-off-by: Dhruva Gole d-gole@ti.com ---
v2: No changes from previous patch. However this DEPENDS on PATCH 1/2 of the same series. Hence disregard the previously sent patch: [PATCH] spi: cadence-qspi: use STIG mode for small reads https://lore.kernel.org/u-boot/20221111110720.283013-1-d-gole@ti.com/T/#u
drivers/spi/cadence_qspi.c | 17 ++++++++++++++++- 1 file changed, 16 insertions(+), 1 deletion(-)
diff --git a/drivers/spi/cadence_qspi.c b/drivers/spi/cadence_qspi.c index ab0a681c8376..6f2924fe4515 100644 --- a/drivers/spi/cadence_qspi.c +++ b/drivers/spi/cadence_qspi.c @@ -307,7 +307,22 @@ static int cadence_spi_mem_exec_op(struct spi_slave *spi, priv->is_decoded_cs);
if (op->data.dir == SPI_MEM_DATA_IN && op->data.buf.in) { - if (!op->addr.nbytes) + /* + * In some cases there is a layer of digital logic in front of the QSPI + * /OSPI Driver when used in DAC mode. This digital logic layer ensures + * that even if we are trying to read 1 or 2 bytes of data, it will + * always align it to 4 bytes from a 4byte aligned address. In some + * flash chips like cypress for example, if we try to read some regs + * in DAC mode then it keeps sending the value of the first register + * who was requested and inorder to read the next register we have to + * stop and re-initiate a new transaction. + * This causes wrong registers values to be read than what is desired + * when registers are read in DAC mode. Hence if the data.nbytes + * is very less then do not use DAC mode. Registers are generally only + * 1-2 bytes and thus switching to STIG mode will be a work around. + */ + if (!op->addr.nbytes || + op->data.nbytes < CQSPI_STIG_DATA_LEN_MAX) mode = CQSPI_STIG_READ; else mode = CQSPI_READ;