spi: add loopback test driver to allow for spi_master regression tests

This driver is submitting lots of distinct spi-messages messages
with all kinds of alignments and length pattern.
Also distinct kinds of transfer pattern tests are implemented
(rx, tx, rx/tx, tx+tx, tx+rx,...)

Right now on a raspberry pi 752 distinct spi_messages are executed
in 13 different scenarios.

Configuration of additional test-pattern is easy, so that when
new bugs in drivers get detected the relevant transfer pattern can
also get added to the test framework, so that such situations are
detected in other drivers as well.

The idea behind this driver is to make it possible to also detect
regressions in spi_master implementations when changes occur.
Potentially these tests could get executed automatically in a
test-server-farm.
Signed-off-by: Martin Sperl <kernel@martin.sperl.org>
Signed-off-by: Mark Brown <broonie@kernel.org>

drivers/spi/spi-test.h

+/*
+ *  linux/drivers/spi/spi-test.h
+ *
+ *  (c) Martin Sperl <kernel@martin.sperl.org>
+ *
+ *  spi_test definitions
+ *
+ *  This program is free software; you can redistribute it and/or modify
+ *  it under the terms of the GNU General Public License as published by
+ *  the Free Software Foundation; either version 2 of the License, or
+ *  (at your option) any later version.
+ *
+ *  This program is distributed in the hope that it will be useful,
+ *  but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *  GNU General Public License for more details.
+ */
+
+#include <linux/spi/spi.h>
+
+#define SPI_TEST_MAX_TRANSFERS 4
+#define SPI_TEST_MAX_SIZE (32 * PAGE_SIZE)
+#define SPI_TEST_MAX_ITERATE 16
+
+/* the "dummy" start addresses used in spi_test
+ * these addresses get translated at a later stage
+ */
+#define RX_START	BIT(30)
+#define TX_START	BIT(31)
+#define RX(off)		((void *)(RX_START + off))
+#define TX(off)		((void *)(TX_START + off))
+
+/* some special defines for offsets */
+#define SPI_TEST_MAX_SIZE_HALF	BIT(29)
+
+/* detection pattern for unfinished reads...
+ * - 0x00 or 0xff could be valid levels for tx_buf = NULL,
+ * so we do not use either of them
+ */
+#define SPI_TEST_PATTERN_UNWRITTEN 0xAA
+#define SPI_TEST_PATTERN_DO_NOT_WRITE 0x55
+#define SPI_TEST_CHECK_DO_NOT_WRITE 64
+
+/**
+ * struct spi_test - describes a specific (set of) tests to execute
+ *
+ * @description:      description of the test
+ *
+ * @msg:              a template @spi_message usedfor the default settings
+ * @transfers:        array of @spi_transfers that are part of the
+ *                    resulting spi_message. The first transfer with len == 0
+ *                    signifies the end of the list
+ * @transfer_count:   normally computed number of transfers with len > 0
+ *
+ * @run_test:         run a specific spi_test - this allows to override
+ *                    the default implementation of @spi_test_run_transfer
+ *                    either to add some custom filters for a specific test
+ *                    or to effectively run some very custom tests...
+ * @execute_msg:      run the spi_message for real - this allows to override
+ *                    @spi_test_execute_msg to apply final modifications
+ *                    on the spi_message
+ * @expected_return:  the expected return code - in some cases we want to
+ *                    test also for error conditions
+ *
+ * @iterate_len:      list of length to iterate on (in addition to the
+ *                    explicitly set @spi_transfer.len)
+ * @iterate_tx_align: change the alignment of @spi_transfer.tx_buf
+ *                    for all values in the below range if set.
+ *                    the ranges are:
+ *                    [0 : @spi_master.dma_alignment[ if set
+ *                    [0 : iterate_tx_align[ if unset
+ * @iterate_rx_align: change the alignment of @spi_transfer.rx_buf
+ *                    see @iterate_tx_align for details
+ * @iterate_transfer_mask: the bitmask of transfers to which the iterations
+ *                         apply - if 0, then it applies to all transfer
+ *
+ * @fill_option:      define the way how tx_buf is filled
+ * @fill_pattern:     fill pattern to apply to the tx_buf
+ *                    (used in some of the @fill_options)
+ */
+
+struct spi_test {
+	char description[64];
+	struct spi_message msg;
+	struct spi_transfer transfers[SPI_TEST_MAX_TRANSFERS];
+	unsigned int transfer_count;
+	int (*run_test)(struct spi_device *spi, struct spi_test *test,
+			void *tx, void *rx);
+	int (*execute_msg)(struct spi_device *spi, struct spi_test *test,
+			   void *tx, void *rx);
+	int expected_return;
+	/* iterate over all the non-zero values */
+	int iterate_len[SPI_TEST_MAX_ITERATE];
+	int iterate_tx_align;
+	int iterate_rx_align;
+	u32 iterate_transfer_mask;
+	/* the tx-fill operation */
+	u32 fill_option;
+#define FILL_MEMSET_8	0	/* just memset with 8 bit */
+#define FILL_MEMSET_16	1	/* just memset with 16 bit */
+#define FILL_MEMSET_24	2	/* just memset with 24 bit */
+#define FILL_MEMSET_32	3	/* just memset with 32 bit */
+#define FILL_COUNT_8	4	/* fill with a 8 byte counter */
+#define FILL_COUNT_16	5	/* fill with a 16 bit counter */
+#define FILL_COUNT_24	6	/* fill with a 24 bit counter */
+#define FILL_COUNT_32	7	/* fill with a 32 bit counter */
+#define FILL_TRANSFER_BYTE_8  8	/* fill with the transfer byte - 8 bit */
+#define FILL_TRANSFER_BYTE_16 9	/* fill with the transfer byte - 16 bit */
+#define FILL_TRANSFER_BYTE_24 10 /* fill with the transfer byte - 24 bit */
+#define FILL_TRANSFER_BYTE_32 11 /* fill with the transfer byte - 32 bit */
+#define FILL_TRANSFER_NUM     16 /* fill with the transfer number */
+	u32 fill_pattern;
+};
+
+/* default implementation for @spi_test.run_test */
+int spi_test_run_test(struct spi_device *spi,
+		      const struct spi_test *test,
+		      void *tx, void *rx);
+
+/* default implementation for @spi_test.execute_msg */
+int spi_test_execute_msg(struct spi_device *spi,
+			 struct spi_test *test,
+			 void *tx, void *rx);
+
+/* function to execute a set of tests */
+int spi_test_run_tests(struct spi_device *spi,
+		       struct spi_test *tests);
+
+/* some of the default @spi_transfer.len to test */
+#define ITERATE_LEN 16, 32, 64, 128, 256, 1024, PAGE_SIZE, 65536
+
+#define ITERATE_MAX_LEN ITERATE_LEN, SPI_TEST_MAX_SIZE
+
+/* the default alignment to test */
+#define ITERATE_ALIGN sizeof(int)