[PATCH linux dev-4.7 v3] drivers/fsi: Increase delay before sampling input on SDA

[Christopher Bostic]

During high cpu loads the SDA in line can shift relative to the
clock signal which can corrupt the received input data.  Slow
down the time to sample input to account for this.

Add sysfs files to adjust the three main openfsi protocol timing
values: clock delay; sample delay; clock off time.

Signed-off-by: Christopher Bostic <cbostic at linux.vnet.ibm.com>
---
v3 - Add sysfs files to adjust protocol timings

v2 - Increase delay for SDA in sampling only.

   - Decrease the original delay for SDA sampling from 1us to 200ns
---
 drivers/fsi/fsi-master-gpio.c | 107 ++++++++++++++++++++++++++++++++++++++++--
 1 file changed, 103 insertions(+), 4 deletions(-)

diff --git a/drivers/fsi/fsi-master-gpio.c b/drivers/fsi/fsi-master-gpio.c
index a8976d5..0907977 100644
--- a/drivers/fsi/fsi-master-gpio.c
+++ b/drivers/fsi/fsi-master-gpio.c
@@ -14,6 +14,7 @@
 #include "fsi-master.h"
 
 #define	FSI_GPIO_STD_DLY	1	/* Standard pin delay in nS */
+#define	FSI_GPIO_SDA_IN_DLY	200	/* Wait to sample SDA line, in nS */
 #define	FSI_ECHO_DELAY_CLOCKS	16	/* Number clocks for echo delay */
 #define	FSI_PRE_BREAK_CLOCKS	50	/* Number clocks to prep for break */
 #define	FSI_BREAK_CLOCKS	256	/* Number of clocks to issue break */
@@ -65,6 +66,10 @@
 
 static DEFINE_SPINLOCK(fsi_gpio_cmd_lock);	/* lock around fsi commands */
 
+static int clock_delay = FSI_GPIO_STD_DLY;
+static int clock_off_time = FSI_GPIO_STD_DLY;
+static int sample_delay = FSI_GPIO_SDA_IN_DLY;
+
 struct fsi_master_gpio {
 	struct fsi_master	master;
 	struct gpio_desc	*gpio_clk;
@@ -86,9 +91,11 @@ static void clock_toggle(struct fsi_master_gpio *master, int count)
 	int i;
 
 	for (i = 0; i < count; i++) {
-		ndelay(FSI_GPIO_STD_DLY);
+		udelay(clock_delay / 1000);
+		ndelay(clock_delay % 1000);
 		gpiod_set_value(master->gpio_clk, 0);
-		ndelay(FSI_GPIO_STD_DLY);
+		udelay(clock_off_time / 1000);
+		ndelay(clock_off_time % 1000);
 		gpiod_set_value(master->gpio_clk, 1);
 	}
 }
@@ -97,7 +104,8 @@ static int sda_in(struct fsi_master_gpio *master)
 {
 	int in;
 
-	ndelay(FSI_GPIO_STD_DLY);
+	udelay(sample_delay / 1000);
+	ndelay(sample_delay % 1000);
 	in = gpiod_get_value(master->gpio_data);
 	return in ? 1 : 0;
 }
@@ -497,10 +505,77 @@ static ssize_t store_scan(struct device *dev,
 
 static DEVICE_ATTR(scan, 0200, NULL, store_scan);
 
+static ssize_t clock_delay_show(struct device *dev,
+				struct device_attribute *attr, char *buf)
+{
+	return snprintf(buf, PAGE_SIZE - 1, "%u\n", clock_delay);
+}
+
+static ssize_t clock_delay_store(struct device *dev,
+				struct device_attribute *attr,
+				const char *buf, size_t count)
+{
+	int rc;
+	unsigned long val = 0;
+
+	rc = kstrtoul(buf, 0, &val);
+	clock_delay = val;
+
+	return count;
+}
+
+DEVICE_ATTR(clock_delay, S_IRUGO | S_IWUSR, clock_delay_show,
+		clock_delay_store);
+
+static ssize_t clock_off_time_show(struct device *dev,
+				struct device_attribute *attr, char *buf)
+{
+	return snprintf(buf, PAGE_SIZE - 1, "%u\n", clock_off_time);
+}
+
+static ssize_t clock_off_time_store(struct device *dev,
+				struct device_attribute *attr,
+				const char *buf, size_t count)
+{
+	int rc;
+	unsigned long val = 0;
+
+	rc = kstrtoul(buf, 0, &val);
+	clock_off_time = val;
+
+	return count;
+}
+
+DEVICE_ATTR(clock_off_time, S_IRUGO | S_IWUSR, clock_off_time_show,
+		clock_off_time_store);
+
+static ssize_t sample_delay_show(struct device *dev,
+				struct device_attribute *attr, char *buf)
+{
+	return snprintf(buf, PAGE_SIZE - 1, "%u\n", sample_delay);
+}
+
+static ssize_t sample_delay_store(struct device *dev,
+				struct device_attribute *attr,
+				const char *buf, size_t count)
+{
+	int rc;
+	unsigned long val = 0;
+
+	rc = kstrtoul(buf, 0, &val);
+	sample_delay = val;
+
+	return count;
+}
+
+DEVICE_ATTR(sample_delay, S_IRUGO | S_IWUSR, sample_delay_show,
+		sample_delay_store);
+
 static int fsi_master_gpio_probe(struct platform_device *pdev)
 {
 	struct fsi_master_gpio *master;
 	struct gpio_desc *gpio;
+	int rc;
 
 	master = devm_kzalloc(&pdev->dev, sizeof(*master), GFP_KERNEL);
 	if (!master)
@@ -548,8 +623,29 @@ static int fsi_master_gpio_probe(struct platform_device *pdev)
 	master->master.send_break = fsi_master_gpio_break;
 	master->master.link_enable = fsi_master_gpio_link_enable;
 	platform_set_drvdata(pdev, master);
+	rc = device_create_file(&pdev->dev, &dev_attr_clock_off_time);
+	if (rc)
+		goto done;
+	rc = device_create_file(&pdev->dev, &dev_attr_clock_delay);
+	if (rc)
+		goto rem_clock_off;
+	rc = device_create_file(&pdev->dev, &dev_attr_sample_delay);
+	if (rc)
+		goto rem_clock_delay;
+	rc = device_create_file(&pdev->dev, &dev_attr_scan);
+	if (rc)
+		goto rem_sample_delay;
 
-	return device_create_file(&pdev->dev, &dev_attr_scan);
+	return rc;
+
+rem_sample_delay:
+	device_remove_file(&pdev->dev, &dev_attr_sample_delay);
+rem_clock_delay:
+	device_remove_file(&pdev->dev, &dev_attr_clock_delay);
+rem_clock_off:
+	device_remove_file(&pdev->dev, &dev_attr_clock_off_time);
+done:
+	return rc;
 }
 
 
@@ -576,6 +672,9 @@ static int fsi_master_gpio_remove(struct platform_device *pdev)
 		devm_gpiod_put(&pdev->dev, master->gpio_mux);
 	}
 	fsi_master_unregister(&master->master);
+	device_remove_file(&pdev->dev, &dev_attr_clock_off_time);
+	device_remove_file(&pdev->dev, &dev_attr_clock_delay);
+	device_remove_file(&pdev->dev, &dev_attr_sample_delay);
 	device_remove_file(&pdev->dev, &dev_attr_scan);
 
 	return 0;
-- 
1.8.2.2