Re: [PATCH v7 2/2] trigger: ledtrig-tty: add additional modes

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On 06. 03. 23, 10:04, Lee Jones wrote:
On Mon, 06 Mar 2023, Jiri Slaby wrote:

On 03. 03. 23, 15:11, Lee Jones wrote:
On Wed, 22 Feb 2023, Florian Eckert wrote:
@@ -113,21 +207,38 @@ static void ledtrig_tty_work(struct work_struct *work)
   		trigger_data->tty = tty;
-	ret = tty_get_icount(trigger_data->tty, &icount);
-	if (ret) {
-		dev_info(trigger_data->tty->dev, "Failed to get icount, stopped polling\n");
-		mutex_unlock(&trigger_data->mutex);
-		return;
-	}
-	if (icount.rx != trigger_data->rx ||
-	    icount.tx != trigger_data->tx) {
-		led_set_brightness_sync(trigger_data->led_cdev, LED_ON);
-		trigger_data->rx = icount.rx;
-		trigger_data->tx = icount.tx;
-	} else {
-		led_set_brightness_sync(trigger_data->led_cdev, LED_OFF);
+	switch (trigger_data->mode) {
+	case TTY_LED_CTS:
+		ledtrig_tty_flags(trigger_data, TIOCM_CTS);
+		break;
+	case TTY_LED_DSR:
+		ledtrig_tty_flags(trigger_data, TIOCM_DSR);
+		break;
+	case TTY_LED_CAR:
+		ledtrig_tty_flags(trigger_data, TIOCM_CAR);
+		break;
+	case TTY_LED_RNG:
+		ledtrig_tty_flags(trigger_data, TIOCM_RNG);
+		break;
+	case TTY_LED_CNT:

I believe this requires a 'fall-through' statement.

I don't think this is the case. Isn't fallthrough required only in cases
when there is at least one statement, i.e. a block?

There's no mention of this caveat in the document.

To my untrained eyes, the rule looks fairly explicit, starting with "All".

   All switch/case blocks must end in one of:

   * break;
   * fallthrough;
   * continue;
   * goto <label>;
   * return [expression];

If you're aware of something I'm not, please consider updating the doc.

The magic word in the above is "block", IMO. A block is defined for me as a list of declarations and/or statements. Which is not the case in the above (i.e. in sequential "case"s).

Furthermore, the gcc docs specifically say about fallthrough attribute:
It can only be used in a switch statement (the compiler will issue an error otherwise), after a preceding statement and before a logically succeeding case label, or user-defined label.

While "case X:" is technically a (label) statement, I don't think they were thinking of it as such here due to following "succeeding case label" in the text.

So checking with the code, gcc indeed skips those (should_warn_for_implicit_fallthrough()):
  /* Skip all immediately following labels.  */
  while (!gsi_end_p (gsi)
         && (gimple_code (gsi_stmt (gsi)) == GIMPLE_LABEL
             || gimple_code (gsi_stmt (gsi)) == GIMPLE_PREDICT))
    gsi_next_nondebug (&gsi);

Apart from that, fallthrough only makes the code harder to read:

case X:
case Y:
case Z:


case X:
case Y:
case Z:

The first one is a clear win, IMO, and it's pretty clear that it falls through on purpose. And even for compiler -- it shall not produce a warning in that case.

suse labs

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