109 lines
3.3 KiB
C
109 lines
3.3 KiB
C
/* SPDX-License-Identifier: GPL-2.0 */
|
|
/*
|
|
* Mix this utility code with some glue code to get one of several types of
|
|
* simple SPI master driver. Two do polled word-at-a-time I/O:
|
|
*
|
|
* - GPIO/parport bitbangers. Provide chipselect() and txrx_word[](),
|
|
* expanding the per-word routines from the inline templates below.
|
|
*
|
|
* - Drivers for controllers resembling bare shift registers. Provide
|
|
* chipselect() and txrx_word[](), with custom setup()/cleanup() methods
|
|
* that use your controller's clock and chipselect registers.
|
|
*
|
|
* Some hardware works well with requests at spi_transfer scope:
|
|
*
|
|
* - Drivers leveraging smarter hardware, with fifos or DMA; or for half
|
|
* duplex (MicroWire) controllers. Provide chipselect() and txrx_bufs(),
|
|
* and custom setup()/cleanup() methods.
|
|
*/
|
|
|
|
/*
|
|
* The code that knows what GPIO pins do what should have declared four
|
|
* functions, ideally as inlines, before including this header:
|
|
*
|
|
* void setsck(struct spi_device *, int is_on);
|
|
* void setmosi(struct spi_device *, int is_on);
|
|
* int getmiso(struct spi_device *);
|
|
* void spidelay(unsigned);
|
|
*
|
|
* setsck()'s is_on parameter is a zero/nonzero boolean.
|
|
*
|
|
* setmosi()'s is_on parameter is a zero/nonzero boolean.
|
|
*
|
|
* getmiso() is required to return 0 or 1 only. Any other value is invalid
|
|
* and will result in improper operation.
|
|
*
|
|
* A non-inlined routine would call bitbang_txrx_*() routines. The
|
|
* main loop could easily compile down to a handful of instructions,
|
|
* especially if the delay is a NOP (to run at peak speed).
|
|
*
|
|
* Since this is software, the timings may not be exactly what your board's
|
|
* 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.
|
|
*/
|
|
|
|
static inline u32
|
|
bitbang_txrx_be_cpha0(struct spi_device *spi,
|
|
unsigned nsecs, unsigned cpol, unsigned flags,
|
|
u32 word, u8 bits)
|
|
{
|
|
/* if (cpol == 0) this is SPI_MODE_0; else this is SPI_MODE_2 */
|
|
|
|
u32 oldbit = (!(word & (1<<(bits-1)))) << 31;
|
|
/* clock starts at inactive polarity */
|
|
for (word <<= (32 - bits); likely(bits); bits--) {
|
|
|
|
/* setup MSB (to slave) on trailing edge */
|
|
if ((flags & SPI_MASTER_NO_TX) == 0) {
|
|
if ((word & (1 << 31)) != oldbit) {
|
|
setmosi(spi, word & (1 << 31));
|
|
oldbit = word & (1 << 31);
|
|
}
|
|
}
|
|
spidelay(nsecs); /* T(setup) */
|
|
|
|
setsck(spi, !cpol);
|
|
spidelay(nsecs);
|
|
|
|
/* sample MSB (from slave) on leading edge */
|
|
word <<= 1;
|
|
if ((flags & SPI_MASTER_NO_RX) == 0)
|
|
word |= getmiso(spi);
|
|
setsck(spi, cpol);
|
|
}
|
|
return word;
|
|
}
|
|
|
|
static inline u32
|
|
bitbang_txrx_be_cpha1(struct spi_device *spi,
|
|
unsigned nsecs, unsigned cpol, unsigned flags,
|
|
u32 word, u8 bits)
|
|
{
|
|
/* if (cpol == 0) this is SPI_MODE_1; else this is SPI_MODE_3 */
|
|
|
|
u32 oldbit = (!(word & (1<<(bits-1)))) << 31;
|
|
/* clock starts at inactive polarity */
|
|
for (word <<= (32 - bits); likely(bits); bits--) {
|
|
|
|
/* setup MSB (to slave) on leading edge */
|
|
setsck(spi, !cpol);
|
|
if ((flags & SPI_MASTER_NO_TX) == 0) {
|
|
if ((word & (1 << 31)) != oldbit) {
|
|
setmosi(spi, word & (1 << 31));
|
|
oldbit = word & (1 << 31);
|
|
}
|
|
}
|
|
spidelay(nsecs); /* T(setup) */
|
|
|
|
setsck(spi, cpol);
|
|
spidelay(nsecs);
|
|
|
|
/* sample MSB (from slave) on trailing edge */
|
|
word <<= 1;
|
|
if ((flags & SPI_MASTER_NO_RX) == 0)
|
|
word |= getmiso(spi);
|
|
}
|
|
return word;
|
|
}
|