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

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.com


Signed-off-by: default avatarMark Brown <broonie@kernel.org>
parent 568035b0

drivers/spi/spi-bitbang-txrx.h

+4 −2
Original line number Diff line number Diff line
@@ -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;

}