Hi,
I ran into trouble when trying to extend MX28EVK board support for a SPI flash (SST24VF032B).
Some code finally runs into spi_flash_cmd_poll_bit() (spi_flash.c). This function is then used to poll the flash's status register:
int spi_flash_cmd_poll_bit(struct spi_flash *flash, unsigned long timeout, u8 cmd, u8 poll_bit) { struct spi_slave *spi = flash->spi; unsigned long timebase; int ret; u8 status;
ret = spi_xfer(spi, 8, &cmd, NULL, SPI_XFER_BEGIN); if (ret) { debug("SF: Failed to send command %02x: %d\n", cmd, ret); return ret; }
timebase = get_timer(0); do { WATCHDOG_RESET();
ret = spi_xfer(spi, 8, NULL, &status, 0); if (ret) return -1;
if ((status & poll_bit) == 0) break;
} while (get_timer(timebase) < timeout);
spi_xfer(spi, 0, NULL, NULL, SPI_XFER_END);
if ((status & poll_bit) == 0) return 0;
/* Timed out */ debug("SF: time out!\n"); return -1; }
It first asserts the flash's chip select transmits the command (first call to spi_xfer - e.g. read status register) and then reads a single byte in a loop until e.g. the BUSY bit is cleared. Finally it calls spi_xfer(spi, 0, NULL, NULL, SPI_XFER_END) to deassert the SPI flash chip select.
But this last spi_xfer() call does not work with the mxs_spi. You must tell the controller to deassert the select line before the final read cycle! I don't see a way to fix this inside mxs_spi.c:spi_xfer(). These seems to be no way to manually deassert the chip select. Or did I miss something?
Well, with the current code spi_flash_cmd_poll_bit() ends up with an asserted chip select. For SPI flashes this will make the chip behave unexpected on the next command!.
A dirty way would be to change the last call to xpi_xfer (see above) into: spi_xfer(spi, 8, NULL, &status, SPI_XFER_END);
This will result in an additional byte transfer with the select being deasserted finally.
Any better ideas to fix this? I am wondering how SPI flash on the Denx' M28EVK can work.
Matthias