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>

1 files changed, 14 insertions, 10 deletions

diff --git a/drivers/spi/spi_bitbang.c b/drivers/spi/spi_bitbang.c
index 2a5abc08e85..f1db395dd88 100644
--- a/drivers/spi/spi_bitbang.c
+++ b/drivers/spi/spi_bitbang.c
@@ -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