regmap/SoundWire: sdw: add support for SoundWire 1.2 MBQ

The SoundWire 1.1 specification only allowed for reads and writes of
bytes. The SoundWire 1.2 specification adds a new capability to
transfer "Multi-Byte Quantities" (MBQ) across the bus. The transfers
still happens one-byte-at-a-time, but the update is atomic.

For example when writing a 16-bit volume, the first byte transferred
is only taken into account when the second byte is successfully
transferred.

The mechanism is symmetrical for read and writes:
- On a read, the address of the last byte to be read is modified by
setting the MBQ bit
- On a write, the address of all but the last byte to be written are
modified by setting the MBQ bit. The address for the last byte relies
on the MBQ bit being cleared.

The current definitions for MBQ-based controls in the SDCA draft
standard are limited to 16 bits for volumes, so for now this is the
only supported format. An update will be provided if and when support
for 24-bit and 32-bit values is specified by the SDCA standard.

One possible objection is that this code could have been handled with
regmap-sdw.c. However this is a new spec addition not handled by every
SoundWire 1.1 and non-SDCA device, so there's no reason to load code
that will never be used.

Also in practice it's extremely unlikely that CONFIG_REGMAP would not
be selected with CONFIG_REGMAP_MBQ selected. However there's no
functional dependency between the two modules so they can be selected
separately.

Reviewed-by: Rander Wang <rander.wang@linux.intel.com>
Reviewed-by: Guennadi Liakhovetski <guennadi.liakhovetski@linux.intel.com>
Reviewed-by: Kai Vehmanen <kai.vehmanen@linux.intel.com>
Signed-off-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Signed-off-by: Bard Liao <yung-chuan.liao@linux.intel.com>
Reviewed-by: Vinod Koul <vkoul@kernel.org>
Link: https://lore.kernel.org/r/20201103172226.4278-3-yung-chuan.liao@linux.intel.com
Signed-off-by: Mark Brown <broonie@kernel.org>

3 files changed, 107 insertions, 1 deletions

diff --git a/drivers/base/regmap/Kconfig b/drivers/base/regmap/Kconfig
index bcb90d8c3960..50b1e2d06a25 100644
--- a/drivers/base/regmap/Kconfig
+++ b/drivers/base/regmap/Kconfig
@@ -4,7 +4,7 @@
 # subsystems should select the appropriate symbols.
 
 config REGMAP
-	default y if (REGMAP_I2C || REGMAP_SPI || REGMAP_SPMI || REGMAP_W1 || REGMAP_AC97 || REGMAP_MMIO || REGMAP_IRQ || REGMAP_SOUNDWIRE || REGMAP_SCCB || REGMAP_I3C || REGMAP_SPI_AVMM)
+	default y if (REGMAP_I2C || REGMAP_SPI || REGMAP_SPMI || REGMAP_W1 || REGMAP_AC97 || REGMAP_MMIO || REGMAP_IRQ || REGMAP_SOUNDWIRE || REGMAP_SOUNDWIRE_MBQ || REGMAP_SCCB || REGMAP_I3C || REGMAP_SPI_AVMM)
 	select IRQ_DOMAIN if REGMAP_IRQ
 	bool
 
@@ -46,6 +46,10 @@ config REGMAP_SOUNDWIRE
 	tristate
 	depends on SOUNDWIRE
 
+config REGMAP_SOUNDWIRE_MBQ
+	tristate
+	depends on SOUNDWIRE
+
 config REGMAP_SCCB
 	tristate
 	depends on I2C
diff --git a/drivers/base/regmap/Makefile b/drivers/base/regmap/Makefile
index ac1b69ee4051..33f63adb5b3d 100644
--- a/drivers/base/regmap/Makefile
+++ b/drivers/base/regmap/Makefile
@@ -15,6 +15,7 @@ obj-$(CONFIG_REGMAP_MMIO) += regmap-mmio.o
 obj-$(CONFIG_REGMAP_IRQ) += regmap-irq.o
 obj-$(CONFIG_REGMAP_W1) += regmap-w1.o
 obj-$(CONFIG_REGMAP_SOUNDWIRE) += regmap-sdw.o
+obj-$(CONFIG_REGMAP_SOUNDWIRE_MBQ) += regmap-sdw-mbq.o
 obj-$(CONFIG_REGMAP_SCCB) += regmap-sccb.o
 obj-$(CONFIG_REGMAP_I3C) += regmap-i3c.o
 obj-$(CONFIG_REGMAP_SPI_AVMM) += regmap-spi-avmm.o
diff --git a/drivers/base/regmap/regmap-sdw-mbq.c b/drivers/base/regmap/regmap-sdw-mbq.c
new file mode 100644
index 000000000000..8ce30650b97c
--- /dev/null
+++ b/drivers/base/regmap/regmap-sdw-mbq.c
@@ -0,0 +1,101 @@
+// SPDX-License-Identifier: GPL-2.0
+// Copyright(c) 2020 Intel Corporation.
+
+#include <linux/device.h>
+#include <linux/errno.h>
+#include <linux/module.h>
+#include <linux/regmap.h>
+#include <linux/soundwire/sdw.h>
+#include <linux/soundwire/sdw_registers.h>
+#include "internal.h"
+
+static int regmap_sdw_mbq_write(void *context, unsigned int reg, unsigned int val)
+{
+	struct device *dev = context;
+	struct sdw_slave *slave = dev_to_sdw_dev(dev);
+	int ret;
+
+	ret = sdw_write(slave, SDW_SDCA_MBQ_CTL(reg), (val >> 8) & 0xff);
+	if (ret < 0)
+		return ret;
+
+	return sdw_write(slave, reg, val & 0xff);
+}
+
+static int regmap_sdw_mbq_read(void *context, unsigned int reg, unsigned int *val)
+{
+	struct device *dev = context;
+	struct sdw_slave *slave = dev_to_sdw_dev(dev);
+	int read0;
+	int read1;
+
+	read0 = sdw_read(slave, reg);
+	if (read0 < 0)
+		return read0;
+
+	read1 = sdw_read(slave, SDW_SDCA_MBQ_CTL(reg));
+	if (read1 < 0)
+		return read1;
+
+	*val = (read1 << 8) | read0;
+
+	return 0;
+}
+
+static struct regmap_bus regmap_sdw_mbq = {
+	.reg_read = regmap_sdw_mbq_read,
+	.reg_write = regmap_sdw_mbq_write,
+	.reg_format_endian_default = REGMAP_ENDIAN_LITTLE,
+	.val_format_endian_default = REGMAP_ENDIAN_LITTLE,
+};
+
+static int regmap_sdw_mbq_config_check(const struct regmap_config *config)
+{
+	/* MBQ-based controls are only 16-bits for now */
+	if (config->val_bits != 16)
+		return -ENOTSUPP;
+
+	/* Registers are 32 bits wide */
+	if (config->reg_bits != 32)
+		return -ENOTSUPP;
+
+	if (config->pad_bits != 0)
+		return -ENOTSUPP;
+
+	return 0;
+}
+
+struct regmap *__regmap_init_sdw_mbq(struct sdw_slave *sdw,
+				     const struct regmap_config *config,
+				     struct lock_class_key *lock_key,
+				     const char *lock_name)
+{
+	int ret;
+
+	ret = regmap_sdw_mbq_config_check(config);
+	if (ret)
+		return ERR_PTR(ret);
+
+	return __regmap_init(&sdw->dev, &regmap_sdw_mbq,
+			&sdw->dev, config, lock_key, lock_name);
+}
+EXPORT_SYMBOL_GPL(__regmap_init_sdw_mbq);
+
+struct regmap *__devm_regmap_init_sdw_mbq(struct sdw_slave *sdw,
+					  const struct regmap_config *config,
+					  struct lock_class_key *lock_key,
+					  const char *lock_name)
+{
+	int ret;
+
+	ret = regmap_sdw_mbq_config_check(config);
+	if (ret)
+		return ERR_PTR(ret);
+
+	return __devm_regmap_init(&sdw->dev, &regmap_sdw_mbq,
+			&sdw->dev, config, lock_key, lock_name);
+}
+EXPORT_SYMBOL_GPL(__devm_regmap_init_sdw_mbq);
+
+MODULE_DESCRIPTION("Regmap SoundWire MBQ Module");
+MODULE_LICENSE("GPL v2");