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>

diff --git a/drivers/spi/spi_bitbang.c b/drivers/spi/spi_bitbang.c
index 2a5abc0..f1db395 100644 (file)
--- 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