spi: core: add spi_split_transfers_maxwords

Add spi_split_transfers_maxwords() function that splits
spi_transfers transparently into multiple transfers
that are below a given number of SPI words.

This function reuses most of its code from
spi_split_transfers_maxsize() and for transfers with
eight or less bits per word actually behaves the same.

Signed-off-by: Leonard Göhrs <l.goehrs@pengutronix.de>
Link: https://lore.kernel.org/r/20230310092053.1006459-1-l.goehrs@pengutronix.de
Signed-off-by: Mark Brown <broonie@kernel.org>

diff --git a/drivers/spi/spi.c b/drivers/spi/spi.c
index c725b4bab7af41129451d73129d202d528fb804b..9036d7a50674c3fc8a70c599007f2c5990c6e527 100644 (file)
--- a/drivers/spi/spi.c
+++ b/drivers/spi/spi.c
@@ -3622,6 +3622,55 @@ int spi_split_transfers_maxsize(struct spi_controller *ctlr,
 }
 EXPORT_SYMBOL_GPL(spi_split_transfers_maxsize);
 
+
+/**
+ * spi_split_transfers_maxwords - split spi transfers into multiple transfers
+ *                                when an individual transfer exceeds a
+ *                                certain number of SPI words
+ * @ctlr:     the @spi_controller for this transfer
+ * @msg:      the @spi_message to transform
+ * @maxwords: the number of words to limit each transfer to
+ * @gfp:      GFP allocation flags
+ *
+ * Return: status of transformation
+ */
+int spi_split_transfers_maxwords(struct spi_controller *ctlr,
+                                struct spi_message *msg,
+                                size_t maxwords,
+                                gfp_t gfp)
+{
+       struct spi_transfer *xfer;
+
+       /*
+        * Iterate over the transfer_list,
+        * but note that xfer is advanced to the last transfer inserted
+        * to avoid checking sizes again unnecessarily (also xfer does
+        * potentially belong to a different list by the time the
+        * replacement has happened).
+        */
+       list_for_each_entry(xfer, &msg->transfers, transfer_list) {
+               size_t maxsize;
+               int ret;
+
+               if (xfer->bits_per_word <= 8)
+                       maxsize = maxwords;
+               else if (xfer->bits_per_word <= 16)
+                       maxsize = 2 * maxwords;
+               else
+                       maxsize = 4 * maxwords;
+
+               if (xfer->len > maxsize) {
+                       ret = __spi_split_transfer_maxsize(ctlr, msg, &xfer,
+                                                          maxsize, gfp);
+                       if (ret)
+                               return ret;
+               }
+       }
+
+       return 0;
+}
+EXPORT_SYMBOL_GPL(spi_split_transfers_maxwords);
+
 /*-------------------------------------------------------------------------*/
 
 /* Core methods for SPI controller protocol drivers.  Some of the

diff --git a/include/linux/spi/spi.h b/include/linux/spi/spi.h
index 74bff5a2f53d36ccf3fe54fc3cbaaf901f8ddb15..873ced6ae4ca606fbd3936c9f30e5a55a697c652 100644 (file)
--- a/include/linux/spi/spi.h
+++ b/include/linux/spi/spi.h
@@ -1295,6 +1295,10 @@ extern int spi_split_transfers_maxsize(struct spi_controller *ctlr,
                                       struct spi_message *msg,
                                       size_t maxsize,
                                       gfp_t gfp);
+extern int spi_split_transfers_maxwords(struct spi_controller *ctlr,
+                                       struct spi_message *msg,
+                                       size_t maxwords,
+                                       gfp_t gfp);
 
 /*---------------------------------------------------------------------------*/