summaryrefslogtreecommitdiff
path: root/include/linux/spi
diff options
context:
space:
mode:
Diffstat (limited to 'include/linux/spi')
-rw-r--r--include/linux/spi/spi_bitbang.h128
1 files changed, 128 insertions, 0 deletions
diff --git a/include/linux/spi/spi_bitbang.h b/include/linux/spi/spi_bitbang.h
new file mode 100644
index 000000000000..8dfe61a445f4
--- /dev/null
+++ b/include/linux/spi/spi_bitbang.h
@@ -0,0 +1,128 @@
+#ifndef __SPI_BITBANG_H
+#define __SPI_BITBANG_H
+
+/*
+ * 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 chipslect() and txrx_bufs(),
+ * and custom setup()/cleanup() methods.
+ */
+struct spi_bitbang {
+ struct workqueue_struct *workqueue;
+ struct work_struct work;
+
+ spinlock_t lock;
+ struct list_head queue;
+ u8 busy;
+ u8 shutdown;
+ u8 use_dma;
+
+ struct spi_master *master;
+
+ void (*chipselect)(struct spi_device *spi, int is_on);
+
+ int (*txrx_bufs)(struct spi_device *spi, struct spi_transfer *t);
+ u32 (*txrx_word[4])(struct spi_device *spi,
+ unsigned nsecs,
+ u32 word, u8 bits);
+};
+
+/* you can call these default bitbang->master methods from your custom
+ * methods, if you like.
+ */
+extern int spi_bitbang_setup(struct spi_device *spi);
+extern void spi_bitbang_cleanup(const struct spi_device *spi);
+extern int spi_bitbang_transfer(struct spi_device *spi, struct spi_message *m);
+
+/* start or stop queue processing */
+extern int spi_bitbang_start(struct spi_bitbang *spi);
+extern int spi_bitbang_stop(struct spi_bitbang *spi);
+
+#endif /* __SPI_BITBANG_H */
+
+/*-------------------------------------------------------------------------*/
+
+#ifdef EXPAND_BITBANG_TXRX
+
+/*
+ * The code that knows what GPIO pins do what should have declared four
+ * functions, ideally as inlines, before #defining EXPAND_BITBANG_TXRX
+ * and 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);
+ *
+ * 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 make 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,
+ u32 word, u8 bits)
+{
+ /* if (cpol == 0) this is SPI_MODE_0; else this is SPI_MODE_2 */
+
+ /* clock starts at inactive polarity */
+ for (word <<= (32 - bits); likely(bits); bits--) {
+
+ /* setup MSB (to slave) on trailing edge */
+ setmosi(spi, word & (1 << 31));
+ spidelay(nsecs); /* T(setup) */
+
+ setsck(spi, !cpol);
+ spidelay(nsecs);
+
+ /* sample MSB (from slave) on leading edge */
+ word <<= 1;
+ word |= getmiso(spi);
+ setsck(spi, cpol);
+ }
+ return word;
+}
+
+static inline u32
+bitbang_txrx_be_cpha1(struct spi_device *spi,
+ unsigned nsecs, unsigned cpol,
+ u32 word, u8 bits)
+{
+ /* if (cpol == 0) this is SPI_MODE_1; else this is SPI_MODE_3 */
+
+ /* clock starts at inactive polarity */
+ for (word <<= (32 - bits); likely(bits); bits--) {
+
+ /* setup MSB (to slave) on leading edge */
+ setsck(spi, !cpol);
+ setmosi(spi, word & (1 << 31));
+ spidelay(nsecs); /* T(setup) */
+
+ setsck(spi, cpol);
+ spidelay(nsecs);
+
+ /* sample MSB (from slave) on trailing edge */
+ word <<= 1;
+ word |= getmiso(spi);
+ }
+ return word;
+}
+
+#endif /* EXPAND_BITBANG_TXRX */