[PATCH] spi: use linked lists rather than an array

This makes the SPI core and its users access transfers in the SPI message
structure as linked list not as an array, as discussed on LKML.

From: David Brownell <dbrownell@users.sourceforge.net>

  Updates including doc, bugfixes to the list code, add
  spi_message_add_tail().  Plus, initialize things _before_ grabbing the
  locks in some cases (in case it grows more expensive).  This also merges
  some bitbang updates of mine that didn't yet make it into the mm tree.

Signed-off-by: Vitaly Wool <vwool@ru.mvista.com>
Signed-off-by: Dmitry Pervushin <dpervushin@gmail.com>
Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

2 files changed, 60 insertions, 44 deletions

diff --git a/drivers/spi/spi.c b/drivers/spi/spi.c
index 3ecedccdb96c..cdb242de901d 100644
--- a/drivers/spi/spi.c
+++ b/drivers/spi/spi.c
@@ -557,6 +557,17 @@ int spi_write_then_read(struct spi_device *spi,
         if ((n_tx + n_rx) > SPI_BUFSIZ)
                 return -EINVAL;
 
+        spi_message_init(&message);
+        memset(x, 0, sizeof x);
+        if (n_tx) {
+                x[0].len = n_tx;
+                spi_message_add_tail(&x[0], &message);
+        }
+        if (n_rx) {
+                x[1].len = n_rx;
+                spi_message_add_tail(&x[1], &message);
+        }
+
         /* ... unless someone else is using the pre-allocated buffer */
         if (down_trylock(&lock)) {
                 local_buf = kmalloc(SPI_BUFSIZ, GFP_KERNEL);
@@ -565,18 +576,11 @@ int spi_write_then_read(struct spi_device *spi,
         } else
                 local_buf = buf;
 
-        memset(x, 0, sizeof x);
-
         memcpy(local_buf, txbuf, n_tx);
         x[0].tx_buf = local_buf;
-        x[0].len = n_tx;
-
         x[1].rx_buf = local_buf + n_tx;
-        x[1].len = n_rx;
 
         /* do the i/o */
-        message.transfers = x;
-        message.n_transfer = ARRAY_SIZE(x);
         status = spi_sync(spi, &message);
         if (status == 0) {
                 memcpy(rxbuf, x[1].rx_buf, n_rx);
diff --git a/drivers/spi/spi_bitbang.c b/drivers/spi/spi_bitbang.c
index 44aff198eb96..f037e5593269 100644
--- a/drivers/spi/spi_bitbang.c
+++ b/drivers/spi/spi_bitbang.c
@@ -146,6 +146,9 @@ int spi_bitbang_setup(struct spi_device *spi)
         struct spi_bitbang_cs   *cs = spi->controller_state;
         struct spi_bitbang      *bitbang;
 
+        if (!spi->max_speed_hz)
+                return -EINVAL;
+
         if (!cs) {
                 cs = kzalloc(sizeof *cs, SLAB_KERNEL);
                 if (!cs)
@@ -172,13 +175,8 @@ int spi_bitbang_setup(struct spi_device *spi)
         if (!cs->txrx_word)
                 return -EINVAL;
 
-        if (!spi->max_speed_hz)
-                spi->max_speed_hz = 500 * 1000;
-
-        /* nsecs = max(50, (clock period)/2), be optimistic */
+        /* nsecs = (clock period)/2 */
         cs->nsecs = (1000000000/2) / (spi->max_speed_hz);
-        if (cs->nsecs < 50)
-                cs->nsecs = 50;
         if (cs->nsecs > MAX_UDELAY_MS * 1000)
                 return -EINVAL;
 
@@ -194,7 +192,7 @@ int spi_bitbang_setup(struct spi_device *spi)
         /* deselect chip (low or high) */
         spin_lock(&bitbang->lock);
         if (!bitbang->busy) {
-                bitbang->chipselect(spi, 0);
+                bitbang->chipselect(spi, BITBANG_CS_INACTIVE);
                 ndelay(cs->nsecs);
         }
         spin_unlock(&bitbang->lock);
@@ -244,9 +242,9 @@ static void bitbang_work(void *_bitbang)
                 struct spi_message      *m;
                 struct spi_device       *spi;
                 unsigned                nsecs;
-                struct spi_transfer     *t;
+                struct spi_transfer     *t = NULL;
                 unsigned                tmp;
-                unsigned                chipselect;
+                unsigned                cs_change;
                 int                     status;
 
                 m = container_of(bitbang->queue.next, struct spi_message,
@@ -254,37 +252,49 @@ static void bitbang_work(void *_bitbang)
                 list_del_init(&m->queue);
                 spin_unlock_irqrestore(&bitbang->lock, flags);
 
-// FIXME this is made-up
-nsecs = 100;
+                /* FIXME this is made-up ... the correct value is known to
+                 * word-at-a-time bitbang code, and presumably chipselect()
+                 * should enforce these requirements too?
+                 */
+                nsecs = 100;
 
                 spi = m->spi;
-                t = m->transfers;
                 tmp = 0;
-                chipselect = 0;
+                cs_change = 1;
                 status = 0;
 
-                for (;;t++) {
+                list_for_each_entry (t, &m->transfers, transfer_list) {
                         if (bitbang->shutdown) {
                                 status = -ESHUTDOWN;
                                 break;
                         }
 
-                        /* set up default clock polarity, and activate chip */
-                        if (!chipselect) {
-                                bitbang->chipselect(spi, 1);
+                        /* set up default clock polarity, and activate chip;
+                         * this implicitly updates clock and spi modes as
+                         * previously recorded for this device via setup().
+                         * (and also deselects any other chip that might be
+                         * selected ...)
+                         */
+                        if (cs_change) {
+                                bitbang->chipselect(spi, BITBANG_CS_ACTIVE);
                                 ndelay(nsecs);
                         }
+                        cs_change = t->cs_change;
                         if (!t->tx_buf && !t->rx_buf && t->len) {
                                 status = -EINVAL;
                                 break;
                         }
 
-                        /* transfer data */
+                        /* transfer data.  the lower level code handles any
+                         * new dma mappings it needs. our caller always gave
+                         * us dma-safe buffers.
+                         */
                         if (t->len) {
-                                /* FIXME if bitbang->use_dma, dma_map_single()
-                                 * before the transfer, and dma_unmap_single()
-                                 * afterwards, for either or both buffers...
+                                /* REVISIT dma API still needs a designated
+                                 * DMA_ADDR_INVALID; ~0 might be better.
                                  */
+                                if (!m->is_dma_mapped)
+                                        t->rx_dma = t->tx_dma = 0;
                                 status = bitbang->txrx_bufs(spi, t);
                         }
                         if (status != t->len) {
@@ -299,29 +309,31 @@ nsecs = 100;
                         if (t->delay_usecs)
                                 udelay(t->delay_usecs);
 
-                        tmp++;
-                        if (tmp >= m->n_transfer)
-                                break;
-
-                        chipselect = !t->cs_change;
-                        if (chipselect);
+                        if (!cs_change)
                                 continue;
+                        if (t->transfer_list.next == &m->transfers)
+                                break;
 
-                        bitbang->chipselect(spi, 0);
-
-                        /* REVISIT do we want the udelay here instead? */
-                        msleep(1);
+                        /* sometimes a short mid-message deselect of the chip
+                         * may be needed to terminate a mode or command
+                         */
+                        ndelay(nsecs);
+                        bitbang->chipselect(spi, BITBANG_CS_INACTIVE);
+                        ndelay(nsecs);
                 }
 
-                tmp = m->n_transfer - 1;
-                tmp = m->transfers[tmp].cs_change;
-
                 m->status = status;
                 m->complete(m->context);
 
-                ndelay(2 * nsecs);
-                bitbang->chipselect(spi, status == 0 && tmp);
-                ndelay(nsecs);
+                /* normally deactivate chipselect ... unless no error and
+                 * cs_change has hinted that the next message will probably
+                 * be for this chip too.
+                 */
+                if (!(status == 0 && cs_change)) {
+                        ndelay(nsecs);
+                        bitbang->chipselect(spi, BITBANG_CS_INACTIVE);
+                        ndelay(nsecs);
+                }
 
                 spin_lock_irqsave(&bitbang->lock, flags);
         }