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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: 1847e3046c ("spi: gpio: Implement LSB First bitbang support")
Signed-off-by: Robin Murphy <robin.murphy@arm.com>
Link: https://lore.kernel.org/r/28324d8622da80461cce35a82859b003d6f6c4b0.1659538737.git.robin.murphy@arm.com
Signed-off-by: Mark Brown <broonie@kernel.org>
This commit is contained in:
Robin Murphy 2022-08-03 15:58:57 +01:00 committed by Mark Brown
parent 568035b01c
commit 46f7ac3d78
No known key found for this signature in database
GPG Key ID: 24D68B725D5487D0
1 changed files with 4 additions and 2 deletions
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6
drivers/spi/spi-bitbang-txrx.h
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@ -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;
}