jtag: simplify management of non-implemented handlers

There is just a single entry point for the jtag API .khz(),
.speed_div(), .power_dropout(), .srst_asserted().

Simplify the code by in-lining the default handler.
The overall code behaviour is not changed.
This change prevents modifying at run-time the content of
struct jtag_interface.

Inspired from change http://openocd.zylin.com/943
by Evan Hunter <ehunter@broadcom.com>

Change-Id: I09aeb76d614db57b1884ac7ee9f00c152cd77849
Signed-off-by: Antonio Borneo <borneo.antonio@gmail.com>
Reviewed-on: http://openocd.zylin.com/4892
Tested-by: jenkins
Reviewed-by: Tomas Vanek <vanekt@fbl.cz>

src/jtag/adapter.c

@@ -66,30 +66,6 @@ static int jim_adapter_name(Jim_Interp *interp, int argc, Jim_Obj * const *argv)
 	return JIM_OK;
 }
 
-static int default_khz(int khz, int *jtag_speed)
-{
-	LOG_ERROR("Translation from khz to jtag_speed not implemented");
-	return ERROR_FAIL;
-}
-
-static int default_speed_div(int speed, int *khz)
-{
-	LOG_ERROR("Translation from jtag_speed to khz not implemented");
-	return ERROR_FAIL;
-}
-
-static int default_power_dropout(int *dropout)
-{
-	*dropout = 0; /* by default we can't detect power dropout */
-	return ERROR_OK;
-}
-
-static int default_srst_asserted(int *srst_asserted)
-{
-	*srst_asserted = 0; /* by default we can't detect srst asserted */
-	return ERROR_OK;
-}
-
 COMMAND_HANDLER(interface_transport_command)
 {
 	char **transports;
@@ -158,21 +134,8 @@ COMMAND_HANDLER(handle_interface_command)
 			LOG_WARNING("Adapter driver '%s' did not declare "
 				"which transports it allows; assuming "
 				"legacy JTAG-only", jtag_interface->name);
-		retval = allow_transports(CMD_CTX, jtag_interface->transports
+		return allow_transports(CMD_CTX, jtag_interface->transports
 						? jtag_interface->transports : jtag_only);
-			if (ERROR_OK != retval)
-				return retval;
-
-		if (jtag_interface->khz == NULL)
-			jtag_interface->khz = default_khz;
-		if (jtag_interface->speed_div == NULL)
-			jtag_interface->speed_div = default_speed_div;
-		if (jtag_interface->power_dropout == NULL)
-			jtag_interface->power_dropout = default_power_dropout;
-		if (jtag_interface->srst_asserted == NULL)
-			jtag_interface->srst_asserted = default_srst_asserted;
-
-		return ERROR_OK;
 	}
 
 	/* no valid interface was found (i.e. the configuration option,

src/jtag/core.c

@@ -1611,14 +1611,18 @@ static int adapter_khz_to_speed(unsigned khz, int *speed)
 {
 	LOG_DEBUG("convert khz to interface specific speed value");
 	speed_khz = khz;
-	if (jtag != NULL) {
+	if (!jtag)
+		return ERROR_OK;
 	LOG_DEBUG("have interface set up");
+	if (!jtag->khz) {
+		LOG_ERROR("Translation from khz to jtag_speed not implemented");
+		return ERROR_FAIL;
+	}
 	int speed_div1;
 	int retval = jtag->khz(jtag_get_speed_khz(), &speed_div1);
 	if (ERROR_OK != retval)
 		return retval;
 	*speed = speed_div1;
-	}
 	return ERROR_OK;
 }
 
@@ -1681,7 +1685,13 @@ int jtag_get_speed_readable(int *khz)
 	int retval = jtag_get_speed(&jtag_speed_var);
 	if (retval != ERROR_OK)
 		return retval;
-	return jtag ? jtag->speed_div(jtag_speed_var, khz) : ERROR_OK;
+	if (!jtag)
+		return ERROR_OK;
+	if (!jtag->speed_div) {
+		LOG_ERROR("Translation from jtag_speed to khz not implemented");
+		return ERROR_FAIL;
+	}
+	return jtag->speed_div(jtag_speed_var, khz);
 }
 
 void jtag_set_verify(bool enable)
@@ -1712,12 +1722,20 @@ int jtag_power_dropout(int *dropout)
 		LOG_ERROR("No Valid JTAG Interface Configured.");
 		exit(-1);
 	}
+	if (jtag->power_dropout)
 		return jtag->power_dropout(dropout);
+
+	*dropout = 0; /* by default we can't detect power dropout */
+	return ERROR_OK;
 }
 
 int jtag_srst_asserted(int *srst_asserted)
 {
+	if (jtag->srst_asserted)
 		return jtag->srst_asserted(srst_asserted);
+
+	*srst_asserted = 0; /* by default we can't detect srst asserted */
+	return ERROR_OK;
 }
 
 enum reset_types jtag_get_reset_config(void)