[PATCH linux dev-4.10 6/7] drivers/fsi: GPIO stability changes for Cronus/Hostboot

[Christopher Bostic]

Improve stability in the FSI protocol by re-ordering the clocking
delays. Increase clocking delays to 3 microseconds.  Remove
delay prior to sampling input - now redundant given new clocking
delay order.

New effective delay per clock toggle is now 6 microseconds.
Previous clocking summed up to 3 nS but real time measurements
of each 1 nS delay actually was approx 1.8 microseconds.
Previous total delay was then 1.8 * 3 = 5.4 microseconds.

Signed-off-by: Christopher Bostic <cbostic at linux.vnet.ibm.com>
---
 drivers/fsi/fsi-master-gpio.c | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/drivers/fsi/fsi-master-gpio.c b/drivers/fsi/fsi-master-gpio.c
index d5cce88..ef209ef 100644
--- a/drivers/fsi/fsi-master-gpio.c
+++ b/drivers/fsi/fsi-master-gpio.c
@@ -14,7 +14,7 @@
 
 #include "fsi-master.h"
 
-#define	FSI_GPIO_STD_DLY	1	/* Standard pin delay in nS */
+#define	FSI_GPIO_STD_DLY	3	/* Standard pin delay in uS */
 #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 */
@@ -76,10 +76,10 @@ static void clock_toggle(struct fsi_master_gpio *master, int count)
 	int i;
 
 	for (i = 0; i < count; i++) {
-		ndelay(FSI_GPIO_STD_DLY);
 		gpiod_set_value(master->gpio_clk, 0);
-		ndelay(FSI_GPIO_STD_DLY);
+		udelay(FSI_GPIO_STD_DLY);
 		gpiod_set_value(master->gpio_clk, 1);
+		udelay(FSI_GPIO_STD_DLY);
 	}
 }
 
@@ -87,7 +87,6 @@ static int sda_in(struct fsi_master_gpio *master)
 {
 	int in;
 
-	ndelay(FSI_GPIO_STD_DLY);
 	in = gpiod_get_value(master->gpio_data);
 	return in ? 1 : 0;
 }
-- 
1.8.2.2