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spi: bitbang bugfix in message setup 

Bugfix to spi_bitbang infrastructure: make sure to always set transfer
parameters on the first pass through the message's per-transfer loop.
This can matter with drivers that replace the per-word or per-buffer
transfer primitives, on busses with multiple SPI devices.

Previously, this could have started messages using the settings left after
previous messages.  The problem was observed when a high speed chip
(m25p80 type flash) was running very slowly because a low speed device
(avr8 microcontroller) had previously used the bus.  Similar faults could
have driven the low speed device too fast, or used an unexpected word
size.

Acked-by: Steven A. Falco <sfalco@harris.com>
Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
David Brownell 2009-06-30 11:41:30 -07:00 committed by Linus Torvalds
parent 537a1bf059
commit 529ba0d966
1 changed files with 14 additions and 10 deletions
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24
drivers/spi/spi_bitbang.c
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@ -258,6 +258,11 @@ static void bitbang_work(struct work_struct *work)
struct spi_bitbang *bitbang =
container_of(work, struct spi_bitbang, work);
unsigned long flags;
int do_setup = -1;
int (*setup_transfer)(struct spi_device *,
struct spi_transfer *);
setup_transfer = bitbang->setup_transfer;
spin_lock_irqsave(&bitbang->lock, flags);
bitbang->busy = 1;
@ -269,8 +274,6 @@ static void bitbang_work(struct work_struct *work)
unsigned tmp;
unsigned cs_change;
int status;
int (*setup_transfer)(struct spi_device *,
struct spi_transfer *);
m = container_of(bitbang->queue.next, struct spi_message,
queue);
@ -287,19 +290,19 @@ static void bitbang_work(struct work_struct *work)
tmp = 0;
cs_change = 1;
status = 0;
setup_transfer = NULL;
list_for_each_entry (t, &m->transfers, transfer_list) {
/* override or restore speed and wordsize */
if (t->speed_hz || t->bits_per_word) {
setup_transfer = bitbang->setup_transfer;
/* override speed or wordsize? */
if (t->speed_hz || t->bits_per_word)
do_setup = 1;
/* init (-1) or override (1) transfer params */
if (do_setup != 0) {
if (!setup_transfer) {
status = -ENOPROTOOPT;
break;
}
}
if (setup_transfer) {
status = setup_transfer(spi, t);
if (status < 0)
break;
@ -363,9 +366,10 @@ static void bitbang_work(struct work_struct *work)
m->status = status;
m->complete(m->context);
/* restore speed and wordsize */
if (setup_transfer)
/* restore speed and wordsize if it was overridden */
if (do_setup == 1)
setup_transfer(spi, NULL);
do_setup = 0;
/* normally deactivate chipselect ... unless no error and
* cs_change has hinted that the next message will probably