This is a note to let you know that I've just added the patch titled
spi: spi-fsl-spi: allow changing bits_per_word while CS is still active
to the 4.19-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
spi-spi-fsl-spi-allow-changing-bits_per_word-while-cs-is-still-active.patch
and it can be found in the queue-4.19 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From a798a7086c38d91d304132c194cff9f02197f5cd Mon Sep 17 00:00:00 2001
From: Rasmus Villemoes <rasmus.villemoes@xxxxxxxxx>
Date: Wed, 27 Mar 2019 14:30:51 +0000
Subject: spi: spi-fsl-spi: allow changing bits_per_word while CS is still active
From: Rasmus Villemoes <rasmus.villemoes@xxxxxxxxx>
commit a798a7086c38d91d304132c194cff9f02197f5cd upstream.
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 <rasmus.villemoes@xxxxxxxxx>
Signed-off-by: Mark Brown <broonie@xxxxxxxxxx>
Cc: Christophe Leroy <christophe.leroy@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
drivers/spi/spi-fsl-spi.c | 11 ++++++-----
1 file changed, 6 insertions(+), 5 deletions(-)
--- a/drivers/spi/spi-fsl-spi.c
+++ b/drivers/spi/spi-fsl-spi.c
@@ -339,7 +339,7 @@ static int fsl_spi_do_one_msg(struct spi
struct spi_transfer *t, *first;
unsigned int cs_change;
const int nsecs = 50;
- int status;
+ int status, last_bpw;
/*
* In CPU mode, optimize large byte transfers to use larger
@@ -378,21 +378,22 @@ static int fsl_spi_do_one_msg(struct spi
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);
Patches currently in stable-queue which might be from rasmus.villemoes@xxxxxxxxx are
queue-4.19/spi-spi-fsl-spi-relax-message-sanity-checking-a-little.patch
queue-4.19/spi-spi-fsl-spi-remove-always-true-conditional-in-fsl_spi_do_one_msg.patch
queue-4.19/spi-spi-fsl-spi-allow-changing-bits_per_word-while-cs-is-still-active.patch
