From a798a7086c38d91d304132c194cff9f02197f5cd Mon Sep 17 00:00:00 2001 From: Rasmus Villemoes Date: Wed, 27 Mar 2019 14:30:51 +0000 Subject: [PATCH] spi: spi-fsl-spi: allow changing bits_per_word while CS is still active Commit c9bfcb315104 (spi_mpc83xx: much improved driver) introduced logic to ensure bits_per_word and speed_hz stay the same for a series of spi_transfers with CS active, arguing that The current driver may cause glitches on SPI CLK line since one must disable the SPI controller before changing any HW settings. This sounds quite reasonable. So this is a quite naive attempt at relaxing this sanity checking to only ensure that speed_hz is constant - in the faint hope that if we do not causes changes to the clock-related fields of the SPMODE register (DIV16 and PM), those glitches won't appear. The purpose of this change is to allow automatically optimizing large transfers to use 32 bits-per-word; taking one interrupt for every byte is extremely slow. Signed-off-by: Rasmus Villemoes Signed-off-by: Mark Brown --- drivers/spi/spi-fsl-spi.c | 11 ++++++----- 1 file changed, 6 insertions(+), 5 deletions(-) diff --git a/drivers/spi/spi-fsl-spi.c b/drivers/spi/spi-fsl-spi.c index 481b075689b5..e2b341943796 100644 --- a/drivers/spi/spi-fsl-spi.c +++ b/drivers/spi/spi-fsl-spi.c @@ -367,7 +367,7 @@ static int fsl_spi_do_one_msg(struct spi_master *master, struct spi_transfer *t, *first; unsigned int cs_change; const int nsecs = 50; - int status; + int status, last_bpw; /* Don't allow changes if CS is active */ cs_change = 1; @@ -375,21 +375,22 @@ static int fsl_spi_do_one_msg(struct spi_master *master, if (cs_change) first = t; cs_change = t->cs_change; - if ((first->bits_per_word != t->bits_per_word) || - (first->speed_hz != t->speed_hz)) { + if (first->speed_hz != t->speed_hz) { dev_err(&spi->dev, - "bits_per_word/speed_hz cannot change while CS is active\n"); + "speed_hz cannot change while CS is active\n"); return -EINVAL; } } + last_bpw = -1; cs_change = 1; status = -EINVAL; list_for_each_entry(t, &m->transfers, transfer_list) { - if (cs_change) + if (cs_change || last_bpw != t->bits_per_word) status = fsl_spi_setup_transfer(spi, t); if (status < 0) break; + last_bpw = t->bits_per_word; if (cs_change) { fsl_spi_chipselect(spi, BITBANG_CS_ACTIVE);