This helper converts the given bits per word to bytes. The result
will always be power-of-two, e.g.,

    ===============    =================
    Input (in bits)    Output (in bytes)
    ===============    =================
            0                   0
            5                   1
            9                   2
            2                   4
            3                   8
    ===============    =================

There are a couple of cases in SPI that are using the same approach
and at least one more (in IIO) would benefit of it. Add a helper
for everyone.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
---
 drivers/spi/spi.c       |  2 +-
 include/linux/spi/spi.h | 25 +++++++++++++++++++++++++
 2 files changed, 26 insertions(+), 1 deletion(-)

diff --git a/drivers/spi/spi.c b/drivers/spi/spi.c
index b0e7702951fe..1bc0fdbb1bd7 100644
--- a/drivers/spi/spi.c
+++ b/drivers/spi/spi.c
@@ -3800,7 +3800,7 @@ int spi_split_transfers_maxwords(struct spi_controller *ctlr,
 		size_t maxsize;
 		int ret;
 
-		maxsize = maxwords * roundup_pow_of_two(BITS_TO_BYTES(xfer->bits_per_word));
+		maxsize = maxwords * spi_bpw_to_bytes(xfer->bits_per_word);
 		if (xfer->len > maxsize) {
 			ret = __spi_split_transfer_maxsize(ctlr, msg, &xfer,
 							   maxsize);
diff --git a/include/linux/spi/spi.h b/include/linux/spi/spi.h
index 834a09bd8ccc..2611f86180a3 100644
--- a/include/linux/spi/spi.h
+++ b/include/linux/spi/spi.h
@@ -1340,6 +1340,31 @@ static inline bool spi_is_bpw_supported(struct spi_device *spi, u32 bpw)
 	return false;
 }
 
+/**
+ * spi_bpw_to_bytes - Covert bits per word to bytes
+ * @bpw: Bits per word
+ *
+ * This function converts the given @bpw to bytes. The result is always
+ * power-of-two, e.g.,
+ *
+ *  ===============    =================
+ *  Input (in bits)    Output (in bytes)
+ *  ===============    =================
+ *          0                   0
+ *          5                   1
+ *          9                   2
+ *          2                   4
+ *          3                   8
+ *  ===============    =================
+ *
+ * Returns:
+ * Bytes for the given @bpw.
+ */
+static inline u32 spi_bpw_to_bytes(u32 bpw)
+{
+	return roundup_pow_of_two(BITS_TO_BYTES(bpw));
+}
+
 /**
  * spi_controller_xfer_timeout - Compute a suitable timeout value
  * @ctlr: SPI device
-- 
2.47.2

On Thu, Apr 17, 2025 at 06:17:52PM +0300, Andy Shevchenko wrote:
> This helper converts the given bits per word to bytes. The result
> will always be power-of-two, e.g.,
> 
>     ===============    =================
>     Input (in bits)    Output (in bytes)
>     ===============    =================
>             0                   0
>             5                   1
>             9                   2

>             2                   4
>             3                   8

My gosh, it lost the couple of characters here, should be 21 and 37 respectively...
I'll fix this in v3.

>     ===============    =================

...

> + * This function converts the given @bpw to bytes. The result is always
> + * power-of-two, e.g.,
> + *
> + *  ===============    =================
> + *  Input (in bits)    Output (in bytes)
> + *  ===============    =================
> + *          0                   0
> + *          5                   1
> + *          9                   2

> + *          2                   4
> + *          3                   8

As per above,

> + *  ===============    =================

-- 
With Best Regards,
Andy Shevchenko