Commit 46f7ac3d authored by Robin Murphy's avatar Robin Murphy Committed by Mark Brown

spi: bitbang: Fix lsb-first Rx

Shifting the recieved bit by "bits" inserts it at the top of the
*currently remaining* Tx data, so we end up accumulating the whole
transfer into bit 0 of the output word. Oops.

For the algorithm to work as intended, we need to remember where the
top of the *original* word was, and shift Rx to there.

Fixes: 1847e304 ("spi: gpio: Implement LSB First bitbang support")
Signed-off-by: default avatarRobin Murphy <robin.murphy@arm.com>
Link: https://lore.kernel.org/r/28324d8622da80461cce35a82859b003d6f6c4b0.1659538737.git.robin.murphy@arm.comSigned-off-by: default avatarMark Brown <broonie@kernel.org>
parent 568035b0
......@@ -116,6 +116,7 @@ bitbang_txrx_le_cpha0(struct spi_device *spi,
{
/* if (cpol == 0) this is SPI_MODE_0; else this is SPI_MODE_2 */
u8 rxbit = bits - 1;
u32 oldbit = !(word & 1);
/* clock starts at inactive polarity */
for (; likely(bits); bits--) {
......@@ -135,7 +136,7 @@ bitbang_txrx_le_cpha0(struct spi_device *spi,
/* sample LSB (from slave) on leading edge */
word >>= 1;
if ((flags & SPI_MASTER_NO_RX) == 0)
word |= getmiso(spi) << (bits - 1);
word |= getmiso(spi) << rxbit;
setsck(spi, cpol);
}
return word;
......@@ -148,6 +149,7 @@ bitbang_txrx_le_cpha1(struct spi_device *spi,
{
/* if (cpol == 0) this is SPI_MODE_1; else this is SPI_MODE_3 */
u8 rxbit = bits - 1;
u32 oldbit = !(word & 1);
/* clock starts at inactive polarity */
for (; likely(bits); bits--) {
......@@ -168,7 +170,7 @@ bitbang_txrx_le_cpha1(struct spi_device *spi,
/* sample LSB (from slave) on trailing edge */
word >>= 1;
if ((flags & SPI_MASTER_NO_RX) == 0)
word |= getmiso(spi) << (bits - 1);
word |= getmiso(spi) << rxbit;
}
return word;
}
Markdown is supported
0%
or
You are about to add 0 people to the discussion. Proceed with caution.
Finish editing this message first!
Please register or to comment