Claim the SPI bus before writes if the IMC ROM is present

The SB800 and Hudson now support adding the IMC ROM which runs from the same
chip as coreboot.  When the IMC is running, write or erase commands sent to
the spi bus will fail, and the IMC will die.  To fix this, we send a request
to the IMC to stop fetching from the SPI rom while we write to it. This
process (in one form or another) is required for writes to the SPI bus while
the IMC is running.

Because the IMC can take up to 500ms to respond every time we claim the
bus, this patch tries to keep the number of times we need to do that to a
minimum.  We only need to claim the bus on writes, and using a counter for
the semaphore allows us to call in once to claim the bus at the beginning
of a number of transactions and it will stay claimed until we release it
at the end of the transactions.

Claim() - takes up to 500ms hit
    claim() - no delay
        erase()
    release()
    claim() - no delay
        write()
    release()
Release()

Change-Id: I4e003c5122a2ed47abce57ab8b92dee6aa4713ed
Signed-off-by: Martin Roth <martin@se-eng.com>
Reviewed-on: http://review.coreboot.org/1976
Tested-by: build bot (Jenkins)
Reviewed-by: Patrick Georgi <patrick@georgi-clan.de>

1 files changed, 1 insertions, 0 deletions

diff --git a/src/drivers/spi/sst.c b/src/drivers/spi/sst.c
index 2609591723b2..8cf3f964fd41 100644
--- a/src/drivers/spi/sst.c
+++ b/src/drivers/spi/sst.c
@@ -153,6 +153,7 @@ sst_write(struct spi_flash *flash, u32 offset, size_t len, const void *buf)
 	int ret;
 	u8 cmd[4];
 
+	flash->spi->rw = SPI_WRITE_FLAG;
 	ret = spi_claim_bus(flash->spi);
 	if (ret) {
 		printk(BIOS_WARNING, "SF: Unable to claim SPI bus\n");