| Message ID | 28324d8622da80461cce35a82859b003d6f6c4b0.1659538737.git.robin.murphy@arm.com (mailing list archive) |
|---|---|
| State | Accepted |
| Commit | 46f7ac3d7892e808c9ba01c39da6bb85cda26ecd |
| Headers | show |
| Series | spi: bitbang: Fix lsb-first Rx | expand |
On Wed, Aug 03, 2022 at 03:58:57PM +0100, Robin Murphy wrote: > 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. So if this never worked we presumably have some systems out there which somehow rely on the old behaviour that we need to fix somehow - copying in everyone from the original change... > Fixes: 1847e3046c52 ("spi: gpio: Implement LSB First bitbang support") > Signed-off-by: Robin Murphy <robin.murphy@arm.com> > --- > drivers/spi/spi-bitbang-txrx.h | 6 ++++-- > 1 file changed, 4 insertions(+), 2 deletions(-) > > diff --git a/drivers/spi/spi-bitbang-txrx.h b/drivers/spi/spi-bitbang-txrx.h > index 267342dfa738..2dcbe166df63 100644 > --- a/drivers/spi/spi-bitbang-txrx.h > +++ b/drivers/spi/spi-bitbang-txrx.h > @@ -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; > } > -- > 2.36.1.dirty >
On 2022-08-03 16:02, Mark Brown wrote: > On Wed, Aug 03, 2022 at 03:58:57PM +0100, Robin Murphy wrote: >> 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. > > So if this never worked we presumably have some systems out there which > somehow rely on the old behaviour that we need to fix somehow - copying > in everyone from the original change... Hmm, I can't imagine anyone's relying too critically on data transfer corruption :/ Apparently these TM16x8 chips are the only thing so far to even want lsb-first bitbang support at all, so I strongly suspect I'm the first person to try the receive side of it (since Rockchip's SPI hardware doesn't seem to support 3-wire half-duplex). It actually took me quite a while to figure out that this wasn't my bug in trying to hook up the matrix-keymap stuff, since half the bytes I was expecting to get back do only have bit 0 set anyway. Cheers, Robin. >> Fixes: 1847e3046c52 ("spi: gpio: Implement LSB First bitbang support") >> Signed-off-by: Robin Murphy <robin.murphy@arm.com> >> --- >> drivers/spi/spi-bitbang-txrx.h | 6 ++++-- >> 1 file changed, 4 insertions(+), 2 deletions(-) >> >> diff --git a/drivers/spi/spi-bitbang-txrx.h b/drivers/spi/spi-bitbang-txrx.h >> index 267342dfa738..2dcbe166df63 100644 >> --- a/drivers/spi/spi-bitbang-txrx.h >> +++ b/drivers/spi/spi-bitbang-txrx.h >> @@ -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; >> } >> -- >> 2.36.1.dirty >>
On Wed, Aug 03, 2022 at 04:22:13PM +0100, Robin Murphy wrote: > On 2022-08-03 16:02, Mark Brown wrote: > > So if this never worked we presumably have some systems out there which > > somehow rely on the old behaviour that we need to fix somehow - copying > Hmm, I can't imagine anyone's relying too critically on data transfer > corruption :/ Unless it happens to get corrupted into what is actually wanted - it wouldn't be the first time I've seen driver code bodge around some issue in the core. Doesn't seem super likely here given the nature of the bug but it's alway worth checking.
On Wed, 3 Aug 2022 15:58:57 +0100, Robin Murphy wrote: > 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. > > [...] Applied to https://git.kernel.org/pub/scm/linux/kernel/git/broonie/spi.git for-next Thanks! [1/1] spi: bitbang: Fix lsb-first Rx commit: 46f7ac3d7892e808c9ba01c39da6bb85cda26ecd All being well this means that it will be integrated into the linux-next tree (usually sometime in the next 24 hours) and sent to Linus during the next merge window (or sooner if it is a bug fix), however if problems are discovered then the patch may be dropped or reverted. You may get further e-mails resulting from automated or manual testing and review of the tree, please engage with people reporting problems and send followup patches addressing any issues that are reported if needed. If any updates are required or you are submitting further changes they should be sent as incremental updates against current git, existing patches will not be replaced. Please add any relevant lists and maintainers to the CCs when replying to this mail. Thanks, Mark
diff --git a/drivers/spi/spi-bitbang-txrx.h b/drivers/spi/spi-bitbang-txrx.h index 267342dfa738..2dcbe166df63 100644 --- a/drivers/spi/spi-bitbang-txrx.h +++ b/drivers/spi/spi-bitbang-txrx.h @@ -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; }
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: 1847e3046c52 ("spi: gpio: Implement LSB First bitbang support") Signed-off-by: Robin Murphy <robin.murphy@arm.com> --- drivers/spi/spi-bitbang-txrx.h | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-)