w1: ds2408: make value read-back check a Kconfig option

De-activating this reading back will effectively half the time required
for a write to the output register.

Acked-by: Evgeniy Polyakov <zbr@ioremap.net>
Signed-off-by: Jean-Francois Dagenais <jeff.dagenais@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

2 files changed, 22 insertions, 6 deletions

diff --git a/drivers/w1/slaves/Kconfig b/drivers/w1/slaves/Kconfig
index 762561fbabbf..5e6a3c9e510b 100644
--- a/drivers/w1/slaves/Kconfig
+++ b/drivers/w1/slaves/Kconfig
@@ -22,6 +22,16 @@ config W1_SLAVE_DS2408
           Say Y here if you want to use a 1-wire
           DS2408 8-Channel Addressable Switch device support
 
+config W1_SLAVE_DS2408_READBACK
+        bool "Read-back values written to DS2408's output register"
+        depends on W1_SLAVE_DS2408
+        default y
+        help
+          Enabling this will cause the driver to read back the values written
+          to the chip's output register in order to detect errors.
+
+          This is slower but useful when debugging chips and/or busses.
+
 config W1_SLAVE_DS2413
         tristate "Dual Channel Addressable Switch 0x3a family support (DS2413)"
         help
diff --git a/drivers/w1/slaves/w1_ds2408.c b/drivers/w1/slaves/w1_ds2408.c
index 441ad3a3b586..25a5168ab522 100644
--- a/drivers/w1/slaves/w1_ds2408.c
+++ b/drivers/w1/slaves/w1_ds2408.c
@@ -178,6 +178,15 @@ static ssize_t w1_f29_write_output(
                 w1_write_block(sl->master, w1_buf, 3);
 
                 readBack = w1_read_8(sl->master);
+
+                if (readBack != W1_F29_SUCCESS_CONFIRM_BYTE) {
+                        if (w1_reset_resume_command(sl->master))
+                                goto error;
+                        /* try again, the slave is ready for a command */
+                        continue;
+                }
+
+#ifdef CONFIG_W1_SLAVE_DS2408_READBACK
                 /* here the master could read another byte which
                    would be the PIO reg (the actual pin logic state)
                    since in this driver we don't know which pins are
@@ -186,11 +195,6 @@ static ssize_t w1_f29_write_output(
                 if (w1_reset_resume_command(sl->master))
                         goto error;
 
-                if (readBack != 0xAA) {
-                        /* try again, the slave is ready for a command */
-                        continue;
-                }
-
                 /* go read back the output latches */
                 /* (the direct effect of the write above) */
                 w1_buf[0] = W1_F29_FUNC_READ_PIO_REGS;
@@ -198,7 +202,9 @@ static ssize_t w1_f29_write_output(
                 w1_buf[2] = 0;
                 w1_write_block(sl->master, w1_buf, 3);
                 /* read the result of the READ_PIO_REGS command */
-                if (w1_read_8(sl->master) == *buf) {
+                if (w1_read_8(sl->master) == *buf)
+#endif
+                {
                         /* success! */
                         mutex_unlock(&sl->master->bus_mutex);
                         dev_dbg(&sl->dev,