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spi: gpio: Implement LSB First bitbang support

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Add support for slave DT property spi-lsb-first, i.e., SPI_LSB_FIRST mode.
Duplicate the inline helpers bitbang_txrx_be_cpha{0,1} as LE versions.
Conditionally call them from all the spi-gpio txrx_word callbacks.

Some alternatives to this implementation approach were discussed back
then [0], but eventually it was considered reasonable.

[0] https://lore.kernel.org/linux-arm-kernel/20191212033952.5967-8-afaerber@suse.de/

Signed-off-by: Andreas Färber <afaerber@suse.de>
Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
Tested-by: Christian Hewitt <christianshewitt@gmail.com>
Link: https://lore.kernel.org/r/feac3377-4ad1-77d8-9a18-3588d80fb909@gmail.com
Signed-off-by: Mark Brown <broonie@kernel.org>
This commit is contained in:
Andreas Färber 2022-02-19 14:15:48 +01:00 committed by Mark Brown
parent 5741150c80
commit 1847e3046c
No known key found for this signature in database
GPG key ID: 24D68B725D5487D0
2 changed files with 99 additions and 9 deletions
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66
drivers/spi/spi-bitbang-txrx.h
View file

@ -41,6 +41,8 @@
* chips need ... there may be several reasons you'd need to tweak timings
* in these routines, not just to make it faster or slower to match a
* particular CPU clock rate.
*
* ToDo: Maybe the bitrev macros can be used to improve the code?
*/
static inline u32
@ -106,3 +108,67 @@ bitbang_txrx_be_cpha1(struct spi_device *spi,
}
return word;
}
static inline u32
bitbang_txrx_le_cpha0(struct spi_device *spi,
unsigned int nsecs, unsigned int cpol, unsigned int flags,
u32 word, u8 bits)
{
/* if (cpol == 0) this is SPI_MODE_0; else this is SPI_MODE_2 */
u32 oldbit = !(word & 1);
/* clock starts at inactive polarity */
for (; likely(bits); bits--) {
/* setup LSB (to slave) on trailing edge */
if ((flags & SPI_MASTER_NO_TX) == 0) {
if ((word & 1) != oldbit) {
setmosi(spi, word & 1);
oldbit = word & 1;
}
}
spidelay(nsecs); /* T(setup) */
setsck(spi, !cpol);
spidelay(nsecs);
/* sample LSB (from slave) on leading edge */
word >>= 1;
if ((flags & SPI_MASTER_NO_RX) == 0)
word |= getmiso(spi) << (bits - 1);
setsck(spi, cpol);
}
return word;
}
static inline u32
bitbang_txrx_le_cpha1(struct spi_device *spi,
unsigned int nsecs, unsigned int cpol, unsigned int flags,
u32 word, u8 bits)
{
/* if (cpol == 0) this is SPI_MODE_1; else this is SPI_MODE_3 */
u32 oldbit = !(word & 1);
/* clock starts at inactive polarity */
for (; likely(bits); bits--) {
/* setup LSB (to slave) on leading edge */
setsck(spi, !cpol);
if ((flags & SPI_MASTER_NO_TX) == 0) {
if ((word & 1) != oldbit) {
setmosi(spi, word & 1);
oldbit = word & 1;
}
}
spidelay(nsecs); /* T(setup) */
setsck(spi, cpol);
spidelay(nsecs);
/* sample LSB (from slave) on trailing edge */
word >>= 1;
if ((flags & SPI_MASTER_NO_RX) == 0)
word |= getmiso(spi) << (bits - 1);
}
return word;
}

42
drivers/spi/spi-gpio.c
View file

@ -135,25 +135,37 @@ static inline int getmiso(const struct spi_device *spi)
static u32 spi_gpio_txrx_word_mode0(struct spi_device *spi,
unsigned nsecs, u32 word, u8 bits, unsigned flags)
{
return bitbang_txrx_be_cpha0(spi, nsecs, 0, flags, word, bits);
if (unlikely(spi->mode & SPI_LSB_FIRST))
return bitbang_txrx_le_cpha0(spi, nsecs, 0, flags, word, bits);
else
return bitbang_txrx_be_cpha0(spi, nsecs, 0, flags, word, bits);
}
static u32 spi_gpio_txrx_word_mode1(struct spi_device *spi,
unsigned nsecs, u32 word, u8 bits, unsigned flags)
{
return bitbang_txrx_be_cpha1(spi, nsecs, 0, flags, word, bits);
if (unlikely(spi->mode & SPI_LSB_FIRST))
return bitbang_txrx_le_cpha1(spi, nsecs, 0, flags, word, bits);
else
return bitbang_txrx_be_cpha1(spi, nsecs, 0, flags, word, bits);
}
static u32 spi_gpio_txrx_word_mode2(struct spi_device *spi,
unsigned nsecs, u32 word, u8 bits, unsigned flags)
{
return bitbang_txrx_be_cpha0(spi, nsecs, 1, flags, word, bits);
if (unlikely(spi->mode & SPI_LSB_FIRST))
return bitbang_txrx_le_cpha0(spi, nsecs, 1, flags, word, bits);
else
return bitbang_txrx_be_cpha0(spi, nsecs, 1, flags, word, bits);
}
static u32 spi_gpio_txrx_word_mode3(struct spi_device *spi,
unsigned nsecs, u32 word, u8 bits, unsigned flags)
{
return bitbang_txrx_be_cpha1(spi, nsecs, 1, flags, word, bits);
if (unlikely(spi->mode & SPI_LSB_FIRST))
return bitbang_txrx_le_cpha1(spi, nsecs, 1, flags, word, bits);
else
return bitbang_txrx_be_cpha1(spi, nsecs, 1, flags, word, bits);
}
/*
@ -170,28 +182,40 @@ static u32 spi_gpio_spec_txrx_word_mode0(struct spi_device *spi,
unsigned nsecs, u32 word, u8 bits, unsigned flags)
{
flags = spi->master->flags;
return bitbang_txrx_be_cpha0(spi, nsecs, 0, flags, word, bits);
if (unlikely(spi->mode & SPI_LSB_FIRST))
return bitbang_txrx_le_cpha0(spi, nsecs, 0, flags, word, bits);
else
return bitbang_txrx_be_cpha0(spi, nsecs, 0, flags, word, bits);
}
static u32 spi_gpio_spec_txrx_word_mode1(struct spi_device *spi,
unsigned nsecs, u32 word, u8 bits, unsigned flags)
{
flags = spi->master->flags;
return bitbang_txrx_be_cpha1(spi, nsecs, 0, flags, word, bits);
if (unlikely(spi->mode & SPI_LSB_FIRST))
return bitbang_txrx_le_cpha1(spi, nsecs, 0, flags, word, bits);
else
return bitbang_txrx_be_cpha1(spi, nsecs, 0, flags, word, bits);
}
static u32 spi_gpio_spec_txrx_word_mode2(struct spi_device *spi,
unsigned nsecs, u32 word, u8 bits, unsigned flags)
{
flags = spi->master->flags;
return bitbang_txrx_be_cpha0(spi, nsecs, 1, flags, word, bits);
if (unlikely(spi->mode & SPI_LSB_FIRST))
return bitbang_txrx_le_cpha0(spi, nsecs, 1, flags, word, bits);
else
return bitbang_txrx_be_cpha0(spi, nsecs, 1, flags, word, bits);
}
static u32 spi_gpio_spec_txrx_word_mode3(struct spi_device *spi,
unsigned nsecs, u32 word, u8 bits, unsigned flags)
{
flags = spi->master->flags;
return bitbang_txrx_be_cpha1(spi, nsecs, 1, flags, word, bits);
if (unlikely(spi->mode & SPI_LSB_FIRST))
return bitbang_txrx_le_cpha1(spi, nsecs, 1, flags, word, bits);
else
return bitbang_txrx_be_cpha1(spi, nsecs, 1, flags, word, bits);
}
/*----------------------------------------------------------------------*/
@ -378,7 +402,7 @@ static int spi_gpio_probe(struct platform_device *pdev)
master->bits_per_word_mask = SPI_BPW_RANGE_MASK(1, 32);
master->mode_bits = SPI_3WIRE | SPI_3WIRE_HIZ | SPI_CPHA | SPI_CPOL |
SPI_CS_HIGH;
SPI_CS_HIGH | SPI_LSB_FIRST;
if (!spi_gpio->mosi) {
/* HW configuration without MOSI pin
*