linux-kernel - [PATCH v2 3/3] iio: adc: ad4695: add custom regmap bus callbacks

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Message-Id: <20241113-tgamblin-ad4695_improvements-v2-3-b6bb7c758fc4@baylibre.com>
Date: Wed, 13 Nov 2024 15:53:00 -0500
From: Trevor Gamblin <tgamblin@...libre.com>
To: Lars-Peter Clausen <lars@...afoo.de>, 
 Michael Hennerich <Michael.Hennerich@...log.com>, 
 Nuno Sá <nuno.sa@...log.com>, 
 David Lechner <dlechner@...libre.com>, Jonathan Cameron <jic23@...nel.org>
Cc: Jonathan Cameron <Jonathan.Cameron@...wei.com>, 
 linux-iio@...r.kernel.org, linux-kernel@...r.kernel.org, 
 Trevor Gamblin <tgamblin@...libre.com>
Subject: [PATCH v2 3/3] iio: adc: ad4695: add custom regmap bus callbacks

Add a custom implementation of regmap read/write callbacks using the SPI
bus. This allows them to be performed at a lower SCLK rate than data
reads. Previously, all SPI transfers were being performed at a lower
speed, but with this change sample data is read at the max bus speed
while the register reads/writes remain at the lower rate.

Also remove .can_multi_write from the AD4695 driver's regmap_configs, as
this isn't implemented or needed.

For some background context, see:

https://lore.kernel.org/linux-iio/20241028163907.00007e12@Huawei.com/

Suggested-by: David Lechner <dlechner@...libre.com>
Signed-off-by: Trevor Gamblin <tgamblin@...libre.com>
---
 drivers/iio/adc/Kconfig  |  2 +-
 drivers/iio/adc/ad4695.c | 74 +++++++++++++++++++++++++++++++++++++++++++-----
 2 files changed, 68 insertions(+), 8 deletions(-)

diff --git a/drivers/iio/adc/Kconfig b/drivers/iio/adc/Kconfig
index 6c4e74420fd2..e0f9d01ce37d 100644
--- a/drivers/iio/adc/Kconfig
+++ b/drivers/iio/adc/Kconfig
@@ -51,9 +51,9 @@ config AD4130
 config AD4695
 	tristate "Analog Device AD4695 ADC Driver"
 	depends on SPI
-	select REGMAP_SPI
 	select IIO_BUFFER
 	select IIO_TRIGGERED_BUFFER
+	select REGMAP
 	help
 	  Say yes here to build support for Analog Devices AD4695 and similar
 	  analog to digital converters (ADC).
diff --git a/drivers/iio/adc/ad4695.c b/drivers/iio/adc/ad4695.c
index 4bc800293e60..921d996fff79 100644
--- a/drivers/iio/adc/ad4695.c
+++ b/drivers/iio/adc/ad4695.c
@@ -150,6 +150,8 @@ struct ad4695_state {
 	/* Commands to send for single conversion. */
 	u16 cnv_cmd;
 	u8 cnv_cmd2;
+	/* Buffer for storing data from regmap bus reads/writes */
+	u8 regmap_bus_data[4];
 };
 
 static const struct regmap_range ad4695_regmap_rd_ranges[] = {
@@ -194,7 +196,6 @@ static const struct regmap_config ad4695_regmap_config = {
 	.max_register = AD4695_REG_AS_SLOT(127),
 	.rd_table = &ad4695_regmap_rd_table,
 	.wr_table = &ad4695_regmap_wr_table,
-	.can_multi_write = true,
 };
 
 static const struct regmap_range ad4695_regmap16_rd_ranges[] = {
@@ -226,7 +227,67 @@ static const struct regmap_config ad4695_regmap16_config = {
 	.max_register = AD4695_REG_GAIN_IN(15),
 	.rd_table = &ad4695_regmap16_rd_table,
 	.wr_table = &ad4695_regmap16_wr_table,
-	.can_multi_write = true,
+};
+
+static int ad4695_regmap_bus_reg_write(void *context, const void *data,
+				       size_t count)
+{
+	struct ad4695_state *st = context;
+	struct spi_transfer xfer = {
+			.speed_hz = AD4695_REG_ACCESS_SCLK_HZ,
+			.len = count,
+			.tx_buf = st->regmap_bus_data,
+	};
+
+	if (count > ARRAY_SIZE(st->regmap_bus_data))
+		return -EINVAL;
+
+	memcpy(st->regmap_bus_data, data, count);
+
+	return spi_sync_transfer(st->spi, &xfer, 1);
+}
+
+static int ad4695_regmap_bus_reg_read(void *context, const void *reg,
+				      size_t reg_size, void *val,
+				      size_t val_size)
+{
+	struct ad4695_state *st = context;
+	struct spi_transfer xfers[] = {
+		{
+			.speed_hz = AD4695_REG_ACCESS_SCLK_HZ,
+			.len = reg_size,
+			.tx_buf = &st->regmap_bus_data[0],
+		}, {
+			.speed_hz = AD4695_REG_ACCESS_SCLK_HZ,
+			.len = val_size,
+			.rx_buf = &st->regmap_bus_data[2],
+		},
+	};
+	int ret;
+
+	if (reg_size > 2)
+		return -EINVAL;
+
+	if (val_size > 2)
+		return -EINVAL;
+
+	memcpy(&st->regmap_bus_data[0], reg, reg_size);
+
+	ret = spi_sync_transfer(st->spi, xfers, ARRAY_SIZE(xfers));
+	if (ret)
+		return ret;
+
+	memcpy(val, &st->regmap_bus_data[2], val_size);
+
+	return 0;
+}
+
+static const struct regmap_bus ad4695_regmap_bus = {
+	.write = ad4695_regmap_bus_reg_write,
+	.read = ad4695_regmap_bus_reg_read,
+	.read_flag_mask = 0x80,
+	.reg_format_endian_default = REGMAP_ENDIAN_BIG,
+	.val_format_endian_default = REGMAP_ENDIAN_BIG,
 };
 
 static const struct iio_chan_spec ad4695_channel_template = {
@@ -1061,15 +1122,14 @@ static int ad4695_probe(struct spi_device *spi)
 	if (!st->chip_info)
 		return -EINVAL;
 
-	/* Registers cannot be read at the max allowable speed */
-	spi->max_speed_hz = AD4695_REG_ACCESS_SCLK_HZ;
-
-	st->regmap = devm_regmap_init_spi(spi, &ad4695_regmap_config);
+	st->regmap = devm_regmap_init(dev, &ad4695_regmap_bus, st,
+				      &ad4695_regmap_config);
 	if (IS_ERR(st->regmap))
 		return dev_err_probe(dev, PTR_ERR(st->regmap),
 				     "Failed to initialize regmap\n");
 
-	st->regmap16 = devm_regmap_init_spi(spi, &ad4695_regmap16_config);
+	st->regmap16 = devm_regmap_init(dev, &ad4695_regmap_bus, st,
+					&ad4695_regmap16_config);
 	if (IS_ERR(st->regmap16))
 		return dev_err_probe(dev, PTR_ERR(st->regmap16),
 				     "Failed to initialize regmap16\n");

-- 
2.39.5