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04bb2a031c
This patch adds a new flags argument to bitbang_txrx_be_cpha0 and
bitbang_txrx_be_cpha1 transfer functions. This enables support for
SPI_MASTER_NO_{TX,RX} transfer modes. The change should have no impact
on speed of the existing drivers. bitbank_txrx_* functions are usually
inlined into the drivers. When the argument is equal to constant zero,
the optimizer would be able to eliminate the dead code (flags checks)
easily. Tested on ARM and GCC 4.4.x and in all cases the checks were
eliminated in the inlined function.
Reviewed-by: Kyungmin Park <kyungmin.park@samsung.com>
Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
Acked-by: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Grant Likely <grant.likely@secretlab.ca>
98 lines
3.0 KiB
C
98 lines
3.0 KiB
C
/*
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* Mix this utility code with some glue code to get one of several types of
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* simple SPI master driver. Two do polled word-at-a-time I/O:
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*
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* - GPIO/parport bitbangers. Provide chipselect() and txrx_word[](),
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* expanding the per-word routines from the inline templates below.
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*
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* - Drivers for controllers resembling bare shift registers. Provide
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* chipselect() and txrx_word[](), with custom setup()/cleanup() methods
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* that use your controller's clock and chipselect registers.
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*
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* Some hardware works well with requests at spi_transfer scope:
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*
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* - Drivers leveraging smarter hardware, with fifos or DMA; or for half
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* duplex (MicroWire) controllers. Provide chipselect() and txrx_bufs(),
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* and custom setup()/cleanup() methods.
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*/
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/*
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* The code that knows what GPIO pins do what should have declared four
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* functions, ideally as inlines, before including this header:
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*
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* void setsck(struct spi_device *, int is_on);
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* void setmosi(struct spi_device *, int is_on);
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* int getmiso(struct spi_device *);
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* void spidelay(unsigned);
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*
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* setsck()'s is_on parameter is a zero/nonzero boolean.
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*
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* setmosi()'s is_on parameter is a zero/nonzero boolean.
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*
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* getmiso() is required to return 0 or 1 only. Any other value is invalid
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* and will result in improper operation.
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*
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* A non-inlined routine would call bitbang_txrx_*() routines. The
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* main loop could easily compile down to a handful of instructions,
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* especially if the delay is a NOP (to run at peak speed).
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*
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* Since this is software, the timings may not be exactly what your board's
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* chips need ... there may be several reasons you'd need to tweak timings
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* in these routines, not just make to make it faster or slower to match a
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* particular CPU clock rate.
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*/
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static inline u32
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bitbang_txrx_be_cpha0(struct spi_device *spi,
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unsigned nsecs, unsigned cpol, unsigned flags,
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u32 word, u8 bits)
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{
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/* if (cpol == 0) this is SPI_MODE_0; else this is SPI_MODE_2 */
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/* clock starts at inactive polarity */
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for (word <<= (32 - bits); likely(bits); bits--) {
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/* setup MSB (to slave) on trailing edge */
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if ((flags & SPI_MASTER_NO_TX) == 0)
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setmosi(spi, word & (1 << 31));
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spidelay(nsecs); /* T(setup) */
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setsck(spi, !cpol);
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spidelay(nsecs);
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/* sample MSB (from slave) on leading edge */
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word <<= 1;
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if ((flags & SPI_MASTER_NO_RX) == 0)
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word |= getmiso(spi);
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setsck(spi, cpol);
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}
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return word;
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}
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static inline u32
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bitbang_txrx_be_cpha1(struct spi_device *spi,
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unsigned nsecs, unsigned cpol, unsigned flags,
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u32 word, u8 bits)
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{
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/* if (cpol == 0) this is SPI_MODE_1; else this is SPI_MODE_3 */
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/* clock starts at inactive polarity */
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for (word <<= (32 - bits); likely(bits); bits--) {
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/* setup MSB (to slave) on leading edge */
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setsck(spi, !cpol);
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if ((flags & SPI_MASTER_NO_TX) == 0)
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setmosi(spi, word & (1 << 31));
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spidelay(nsecs); /* T(setup) */
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setsck(spi, cpol);
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spidelay(nsecs);
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/* sample MSB (from slave) on trailing edge */
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word <<= 1;
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if ((flags & SPI_MASTER_NO_RX) == 0)
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word |= getmiso(spi);
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}
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return word;
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}
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