1 files changed, 135 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..c961fe9bf3eb
--- /dev/null
+++ b/include/linux/spi/spi_bitbang.h
@@ -0,0 +1,135 @@
+#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);
+#define BITBANG_CS_ACTIVE       1       /* normally nCS, active low */
+#define BITBANG_CS_INACTIVE     0
+
+        /* txrx_bufs() may handle dma mapping for transfers that don't
+         * already have one (transfer.{tx,rx}_dma is zero), or use PIO
+         */
+        int     (*txrx_bufs)(struct spi_device *spi, struct spi_transfer *t);
+
+        /* txrx_word[SPI_MODE_*]() just looks like a shift register */
+        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 */