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From:   Angel Iglesias <ang.iglesiasg@gmail.com>
To:     linux-iio <linux-iio@vger.kernel.org>
Cc:     Jonathan Cameron <jic23@kernel.org>,
        Lars-Peter Clausen <lars@metafoo.de>,
        Paul Cercueil <paul@crapouillou.net>,
        Ulf Hansson <ulf.hansson@linaro.org>,
        "Rafael J. Wysocki" <rafael.j.wysocki@intel.com>,
        linux-kernel@vger.kernel.org
Subject: [PATCH v5 2/5] iio: pressure: bmp280: Fix alignment for DMA safety
Date:   Sun,  7 Aug 2022 13:55:15 +0200
Message-Id: <49086f5c1401d7d28ebf921a67b49f8403ddb16a.1659872590.git.ang.iglesiasg@gmail.com>
In-Reply-To: <cover.1659872590.git.ang.iglesiasg@gmail.com>
References: <cover.1659872590.git.ang.iglesiasg@gmail.com>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Precedence: bulk

Adds DMA-safe buffers to driver data struct to store raw data from sensors

The multiple buffers used thorough the driver share the same memory
allocated as part of the device data instance. The union containing
the buffers is aligned to allow safe usage with DMA operations, such
as regmap bulk read calls.

Updated measurement and calibration reading functions to use the new,
DMA-safe, buffers.

Suggested-by: Jonathan Cameron <jic23@kernel.org>
Signed-off-by: Angel Iglesias <ang.iglesiasg@gmail.com>
---
 drivers/iio/pressure/bmp280-core.c | 122 ++++++++++++++---------------
 drivers/iio/pressure/bmp280.h      |   3 +
 2 files changed, 64 insertions(+), 61 deletions(-)

diff --git a/drivers/iio/pressure/bmp280-core.c b/drivers/iio/pressure/bmp280-core.c
index a109c2609896..4cd657dcbfed 100644
--- a/drivers/iio/pressure/bmp280-core.c
+++ b/drivers/iio/pressure/bmp280-core.c
@@ -31,6 +31,7 @@
 #include <linux/completion.h>
 #include <linux/pm_runtime.h>
 #include <linux/random.h>
+#include <asm/unaligned.h>
 
 #include "bmp280.h"
 
@@ -106,6 +107,18 @@ struct bmp280_data {
 	 * calculation.
 	 */
 	s32 t_fine;
+
+	/*
+	 * DMA (thus cache coherency maintenance) may require the
+	 * transfer buffers to live in their own cache lines.
+	 */
+	union {
+		/* sensor data buffer */
+		u8 data[3];
+		/* calibration data buffers */
+		__le16 bmp280_cal[BMP280_CONTIGUOUS_CALIB_REGS / 2];
+		__be16 bmp180_cal[BMP180_REG_CALIB_COUNT / 2];
+	} buf __aligned(IIO_DMA_MINALIGN);
 };
 
 struct bmp280_chip_info {
@@ -162,41 +175,29 @@ static int bmp280_read_calib(struct bmp280_data *data, unsigned int chip)
 {
 	int ret;
 	unsigned int tmp;
-	__le16 l16;
-	__be16 b16;
 	struct device *dev = data->dev;
+	__le16 *t_buf = data->buf.bmp280_cal;
+	__le16 *p_buf = &data->buf.bmp280_cal[T3+1];
 	struct bmp280_calib *calib = &data->calib.bmp280;
-	__le16 t_buf[BMP280_COMP_TEMP_REG_COUNT / 2];
-	__le16 p_buf[BMP280_COMP_PRESS_REG_COUNT / 2];
 
 	/* Read temperature calibration values. */
 	ret = regmap_bulk_read(data->regmap, BMP280_REG_COMP_TEMP_START,
-			       t_buf, BMP280_COMP_TEMP_REG_COUNT);
+			       data->buf.bmp280_cal, sizeof(data->buf.bmp280_cal));
 	if (ret < 0) {
 		dev_err(data->dev,
 			"failed to read temperature calibration parameters\n");
 		return ret;
 	}
 
-	/* Toss the temperature calibration data into the entropy pool */
-	add_device_randomness(t_buf, sizeof(t_buf));
+	/* Toss the temperature and pressure calibration data into the entropy pool */
+	add_device_randomness(data->buf.bmp280_cal, sizeof(data->buf.bmp280_cal));
 
+	/* parse temperature calibration data */
 	calib->T1 = le16_to_cpu(t_buf[T1]);
 	calib->T2 = le16_to_cpu(t_buf[T2]);
 	calib->T3 = le16_to_cpu(t_buf[T3]);
 
-	/* Read pressure calibration values. */
-	ret = regmap_bulk_read(data->regmap, BMP280_REG_COMP_PRESS_START,
-			       p_buf, BMP280_COMP_PRESS_REG_COUNT);
-	if (ret < 0) {
-		dev_err(data->dev,
-			"failed to read pressure calibration parameters\n");
-		return ret;
-	}
-
-	/* Toss the pressure calibration data into the entropy pool */
-	add_device_randomness(p_buf, sizeof(p_buf));
-
+	/* parse pressure calibration data */
 	calib->P1 = le16_to_cpu(p_buf[P1]);
 	calib->P2 = le16_to_cpu(p_buf[P2]);
 	calib->P3 = le16_to_cpu(p_buf[P3]);
@@ -224,12 +225,12 @@ static int bmp280_read_calib(struct bmp280_data *data, unsigned int chip)
 	}
 	calib->H1 = tmp;
 
-	ret = regmap_bulk_read(data->regmap, BMP280_REG_COMP_H2, &l16, 2);
+	ret = regmap_bulk_read(data->regmap, BMP280_REG_COMP_H2, data->buf.data, 2);
 	if (ret < 0) {
 		dev_err(dev, "failed to read H2 comp value\n");
 		return ret;
 	}
-	calib->H2 = sign_extend32(le16_to_cpu(l16), 15);
+	calib->H2 = get_unaligned_le16(data->buf.data);
 
 	ret = regmap_read(data->regmap, BMP280_REG_COMP_H3, &tmp);
 	if (ret < 0) {
@@ -238,20 +239,20 @@ static int bmp280_read_calib(struct bmp280_data *data, unsigned int chip)
 	}
 	calib->H3 = tmp;
 
-	ret = regmap_bulk_read(data->regmap, BMP280_REG_COMP_H4, &b16, 2);
+	ret = regmap_bulk_read(data->regmap, BMP280_REG_COMP_H4, data->buf.data, 2);
 	if (ret < 0) {
 		dev_err(dev, "failed to read H4 comp value\n");
 		return ret;
 	}
-	calib->H4 = sign_extend32(((be16_to_cpu(b16) >> 4) & 0xff0) |
-				  (be16_to_cpu(b16) & 0xf), 11);
+	calib->H4 = sign_extend32(((get_unaligned_be16(data->buf.data) >> 4) & 0xff0) |
+				  (get_unaligned_be16(data->buf.data) & 0xf), 11);
 
-	ret = regmap_bulk_read(data->regmap, BMP280_REG_COMP_H5, &l16, 2);
+	ret = regmap_bulk_read(data->regmap, BMP280_REG_COMP_H5, data->buf.data, 2);
 	if (ret < 0) {
 		dev_err(dev, "failed to read H5 comp value\n");
 		return ret;
 	}
-	calib->H5 = sign_extend32(((le16_to_cpu(l16) >> 4) & 0xfff), 11);
+	calib->H5 = sign_extend32(((get_unaligned_le16(data->buf.data) >> 4) & 0xfff), 11);
 
 	ret = regmap_read(data->regmap, BMP280_REG_COMP_H6, &tmp);
 	if (ret < 0) {
@@ -346,16 +347,16 @@ static int bmp280_read_temp(struct bmp280_data *data,
 			    int *val)
 {
 	int ret;
-	__be32 tmp = 0;
 	s32 adc_temp, comp_temp;
 
-	ret = regmap_bulk_read(data->regmap, BMP280_REG_TEMP_MSB, &tmp, 3);
+	ret = regmap_bulk_read(data->regmap, BMP280_REG_TEMP_MSB,
+			       data->buf.data, sizeof(data->buf.data));
 	if (ret < 0) {
 		dev_err(data->dev, "failed to read temperature\n");
 		return ret;
 	}
 
-	adc_temp = be32_to_cpu(tmp) >> 12;
+	adc_temp = get_unaligned_be24(data->buf.data) >> 4;
 	if (adc_temp == BMP280_TEMP_SKIPPED) {
 		/* reading was skipped */
 		dev_err(data->dev, "reading temperature skipped\n");
@@ -379,7 +380,6 @@ static int bmp280_read_press(struct bmp280_data *data,
 			     int *val, int *val2)
 {
 	int ret;
-	__be32 tmp = 0;
 	s32 adc_press;
 	u32 comp_press;
 
@@ -388,13 +388,14 @@ static int bmp280_read_press(struct bmp280_data *data,
 	if (ret < 0)
 		return ret;
 
-	ret = regmap_bulk_read(data->regmap, BMP280_REG_PRESS_MSB, &tmp, 3);
+	ret = regmap_bulk_read(data->regmap, BMP280_REG_PRESS_MSB,
+			       data->buf.data, sizeof(data->buf.data));
 	if (ret < 0) {
 		dev_err(data->dev, "failed to read pressure\n");
 		return ret;
 	}
 
-	adc_press = be32_to_cpu(tmp) >> 12;
+	adc_press = get_unaligned_be24(data->buf.data) >> 4;
 	if (adc_press == BMP280_PRESS_SKIPPED) {
 		/* reading was skipped */
 		dev_err(data->dev, "reading pressure skipped\n");
@@ -410,7 +411,6 @@ static int bmp280_read_press(struct bmp280_data *data,
 
 static int bmp280_read_humid(struct bmp280_data *data, int *val, int *val2)
 {
-	__be16 tmp;
 	int ret;
 	s32 adc_humidity;
 	u32 comp_humidity;
@@ -420,13 +420,14 @@ static int bmp280_read_humid(struct bmp280_data *data, int *val, int *val2)
 	if (ret < 0)
 		return ret;
 
-	ret = regmap_bulk_read(data->regmap, BMP280_REG_HUMIDITY_MSB, &tmp, 2);
+	ret = regmap_bulk_read(data->regmap, BMP280_REG_HUMIDITY_MSB,
+			       data->buf.data, 2);
 	if (ret < 0) {
 		dev_err(data->dev, "failed to read humidity\n");
 		return ret;
 	}
 
-	adc_humidity = be16_to_cpu(tmp);
+	adc_humidity = get_unaligned_be16(data->buf.data);
 	if (adc_humidity == BMP280_HUMIDITY_SKIPPED) {
 		/* reading was skipped */
 		dev_err(data->dev, "reading humidity skipped\n");
@@ -767,7 +768,6 @@ static int bmp180_measure(struct bmp280_data *data, u8 ctrl_meas)
 
 static int bmp180_read_adc_temp(struct bmp280_data *data, int *val)
 {
-	__be16 tmp;
 	int ret;
 
 	ret = bmp180_measure(data,
@@ -776,48 +776,48 @@ static int bmp180_read_adc_temp(struct bmp280_data *data, int *val)
 	if (ret)
 		return ret;
 
-	ret = regmap_bulk_read(data->regmap, BMP180_REG_OUT_MSB, &tmp, 2);
+	ret = regmap_bulk_read(data->regmap, BMP180_REG_OUT_MSB, data->buf.data, 2);
 	if (ret)
 		return ret;
 
-	*val = be16_to_cpu(tmp);
+	*val = get_unaligned_be16(data->buf.data);
 
 	return 0;
 }
 
 static int bmp180_read_calib(struct bmp280_data *data, unsigned int chip)
 {
+	struct bmp180_calib *calib = &data->calib.bmp180;
 	int ret;
 	int i;
-	struct bmp180_calib *calib = &data->calib.bmp180;
-	__be16 buf[BMP180_REG_CALIB_COUNT / 2];
 
-	ret = regmap_bulk_read(data->regmap, BMP180_REG_CALIB_START, buf,
-			       sizeof(buf));
+	ret = regmap_bulk_read(data->regmap, BMP180_REG_CALIB_START,
+			       data->buf.bmp180_cal, sizeof(data->buf.bmp180_cal));
 
 	if (ret < 0)
 		return ret;
 
 	/* None of the words has the value 0 or 0xFFFF */
-	for (i = 0; i < ARRAY_SIZE(buf); i++) {
-		if (buf[i] == cpu_to_be16(0) || buf[i] == cpu_to_be16(0xffff))
+	for (i = 0; i < ARRAY_SIZE(data->buf.bmp180_cal); i++) {
+		if (data->buf.bmp180_cal[i] == cpu_to_be16(0) ||
+		    data->buf.bmp180_cal[i] == cpu_to_be16(0xffff))
 			return -EIO;
 	}
 
 	/* Toss the calibration data into the entropy pool */
-	add_device_randomness(buf, sizeof(buf));
-
-	calib->AC1 = be16_to_cpu(buf[AC1]);
-	calib->AC2 = be16_to_cpu(buf[AC2]);
-	calib->AC3 = be16_to_cpu(buf[AC3]);
-	calib->AC4 = be16_to_cpu(buf[AC4]);
-	calib->AC5 = be16_to_cpu(buf[AC5]);
-	calib->AC6 = be16_to_cpu(buf[AC6]);
-	calib->B1 = be16_to_cpu(buf[B1]);
-	calib->B2 = be16_to_cpu(buf[B2]);
-	calib->MB = be16_to_cpu(buf[MB]);
-	calib->MC = be16_to_cpu(buf[MC]);
-	calib->MD = be16_to_cpu(buf[MD]);
+	add_device_randomness(data->buf.bmp180_cal, sizeof(data->buf.bmp180_cal));
+
+	calib->AC1 = be16_to_cpu(data->buf.bmp180_cal[AC1]);
+	calib->AC2 = be16_to_cpu(data->buf.bmp180_cal[AC2]);
+	calib->AC3 = be16_to_cpu(data->buf.bmp180_cal[AC3]);
+	calib->AC4 = be16_to_cpu(data->buf.bmp180_cal[AC4]);
+	calib->AC5 = be16_to_cpu(data->buf.bmp180_cal[AC5]);
+	calib->AC6 = be16_to_cpu(data->buf.bmp180_cal[AC6]);
+	calib->B1 = be16_to_cpu(data->buf.bmp180_cal[B1]);
+	calib->B2 = be16_to_cpu(data->buf.bmp180_cal[B2]);
+	calib->MB = be16_to_cpu(data->buf.bmp180_cal[MB]);
+	calib->MC = be16_to_cpu(data->buf.bmp180_cal[MC]);
+	calib->MD = be16_to_cpu(data->buf.bmp180_cal[MD]);
 
 	return 0;
 }
@@ -865,9 +865,8 @@ static int bmp180_read_temp(struct bmp280_data *data, int *val)
 
 static int bmp180_read_adc_press(struct bmp280_data *data, int *val)
 {
-	int ret;
-	__be32 tmp = 0;
 	u8 oss = data->oversampling_press;
+	int ret;
 
 	ret = bmp180_measure(data,
 			     FIELD_PREP(BMP180_MEAS_CTRL_MASK, BMP180_MEAS_PRESS) |
@@ -876,11 +875,12 @@ static int bmp180_read_adc_press(struct bmp280_data *data, int *val)
 	if (ret)
 		return ret;
 
-	ret = regmap_bulk_read(data->regmap, BMP180_REG_OUT_MSB, &tmp, 3);
+	ret = regmap_bulk_read(data->regmap, BMP180_REG_OUT_MSB,
+			       data->buf.data, sizeof(data->buf.data));
 	if (ret)
 		return ret;
 
-	*val = (be32_to_cpu(tmp) >> 8) >> (8 - oss);
+	*val = get_unaligned_be24(data->buf.data) >> (8 - oss);
 
 	return 0;
 }
diff --git a/drivers/iio/pressure/bmp280.h b/drivers/iio/pressure/bmp280.h
index 5a19c7d04804..c036c7835004 100644
--- a/drivers/iio/pressure/bmp280.h
+++ b/drivers/iio/pressure/bmp280.h
@@ -32,6 +32,9 @@
 #define BMP280_REG_COMP_PRESS_START	0x8E
 #define BMP280_COMP_PRESS_REG_COUNT	18
 
+#define BMP280_CONTIGUOUS_CALIB_REGS	(BMP280_COMP_TEMP_REG_COUNT \
+					 + BMP280_COMP_PRESS_REG_COUNT)
+
 #define BMP280_FILTER_MASK		GENMASK(4, 2)
 #define BMP280_FILTER_OFF		0
 #define BMP280_FILTER_2X		1
-- 
2.37.1