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USB: serial: io_edgeport: mark expected switch fall-throughs

PATCH In review Gustavo A. R. Silva 2 participants 4 messages Jun 28, 2018 – Jul 2, 2018

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Gustavo A. R. Silva

author
#0 lore raw

PATCH 1/1 USB: serial: io_edgeport: mark expected switch fall-throughs

In preparation to enabling -Wimplicit-fallthrough, mark switch cases where we are expecting to fall through.

Signed-off-by Gustavo A. R. Silva <[email protected]>
---
 drivers/usb/serial/io_edgeport.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)
drivers/usb/serial/io_edgeport.c +2 -2
index 97c69d3..441dab6 100644
@@ -1760,7 +1760,7 @@ static void process_rcvd_data(struct edgeport_serial *edge_serial,
 				edge_serial->rxState = EXPECT_HDR2;
 				break;
 			}
-			/* otherwise, drop on through */
+			/* else: fall through */
 		case EXPECT_HDR2:
 			edge_serial->rxHeader2 = *buffer;
 			++buffer;

@@ -1820,7 +1820,7 @@ static void process_rcvd_data(struct edgeport_serial *edge_serial,
 					edge_serial->rxState = EXPECT_DATA;
 					break;
 				}
-				/* Else, drop through */
+				/* else: fall through */
 			}
 		case EXPECT_DATA: /* Expect data */
 			if (bufferLength < edge_serial->rxBytesRemaining) {
maintainer
#1 lore raw
Quoted 13 lines · Gustavo A. R. Silva

In preparation to enabling -Wimplicit-fallthrough, mark switch cases where we are expecting to fall through.

Signed-off-by Gustavo A. R. Silva <[email protected]>
---
 drivers/usb/serial/io_edgeport.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)
drivers/usb/serial/io_edgeport.c +0 -0
index 97c69d3..441dab6 100644

drivers/usb/serial/io_edgeport.c static void process_rcvd_data(struct edgeport_serial *edge_serial, · line 1763

Quoted 5 lines
drivers/usb/serial/io_edgeport.c +1 -1
@@ -1760,7 +1760,7 @@ static void process_rcvd_data(struct edgeport_serial *edge_serial,
 				edge_serial->rxState = EXPECT_HDR2;
 				break;
 			}
-			/* otherwise, drop on through */
+			/* else: fall through */

This doesn't silence the compiler warning with gcc 7.2.0 as the "else: " pattern isn't recognised.

drivers/usb/serial/io_edgeport.c static void process_rcvd_data(struct edgeport_serial *edge_serial, · line 1824

Quoted 10 lines
drivers/usb/serial/io_edgeport.c +1 -1
 		case EXPECT_HDR2:
 			edge_serial->rxHeader2 = *buffer;
 			++buffer;

@@ -1820,7 +1820,7 @@ static void process_rcvd_data(struct edgeport_serial *edge_serial,
 					edge_serial->rxState = EXPECT_DATA;
 					break;
 				}
-				/* Else, drop through */
+				/* else: fall through */
 			}

And this doesn't work either due to the "else: " as well as the fact that the compiler expects the fallthrough comment to precede the case statement directly (e.g. it would need to be moved out of the else block, but that isn't necessarily desirable as we discussed last year:

	lkml.kernel.org/r/[email protected]

)

drivers/usb/serial/io_edgeport.c static void process_rcvd_data(struct edgeport_serial *edge_serial, · line 1826

Quoted 2 lines
drivers/usb/serial/io_edgeport.c +0 -0
 		case EXPECT_DATA: /* Expect data */
 			if (bufferLength < edge_serial->rxBytesRemaining) {

How do you compile test these these patches?

Thanks,
Johan
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author
#2 lore raw

Hi Johan,

Quoted 9 lines · Johan Hovold
Quoted 8 lines · Gustavo A. R. Silva

In preparation to enabling -Wimplicit-fallthrough, mark switch cases where we are expecting to fall through.

Signed-off-by Gustavo A. R. Silva <[email protected]>
---
 drivers/usb/serial/io_edgeport.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)
Quoted 14 lines

drivers/usb/serial/io_edgeport.c static void process_rcvd_data(struct edgeport_serial *edge_serial, · line 1763

Quoted 10 lines
drivers/usb/serial/io_edgeport.c +1 -1
index 97c69d3..441dab6 100644
@@ -1760,7 +1760,7 @@ static void process_rcvd_data(struct edgeport_serial *edge_serial,
 				edge_serial->rxState = EXPECT_HDR2;
 				break;
 			}
-			/* otherwise, drop on through */
+			/* else: fall through */

This doesn't silence the compiler warning with gcc 7.2.0 as the "else: " pattern isn't recognised.

I'm using level 2:

-Wimplicit-fallthrough=2

The thing here is that some people have pointed out that it can be misleading to place a plain fall-through comment after an if-else code block containing a "break". So, the solution above has proved to be a good one.

Quoted 16 lines

drivers/usb/serial/io_edgeport.c static void process_rcvd_data(struct edgeport_serial *edge_serial, · line 1824

Quoted 10 lines
drivers/usb/serial/io_edgeport.c +1 -1
 		case EXPECT_HDR2:
 			edge_serial->rxHeader2 = *buffer;
 			++buffer;

@@ -1820,7 +1820,7 @@ static void process_rcvd_data(struct edgeport_serial *edge_serial,
 					edge_serial->rxState = EXPECT_DATA;
 					break;
 				}
-				/* Else, drop through */
+				/* else: fall through */
 			}

And this doesn't work either due to the "else: " as well as the fact that the compiler expects the fallthrough comment to precede the case statement directly (e.g. it would need to be moved out of the else block, but that isn't necessarily desirable as we discussed last year:

Quoted 2 lines
	lkml.kernel.org/r/[email protected]

Yes. I'm aware of that. This certainly is still triggering a warning, so I just consider this as a temporal approach. I still need to define how are we going to manage cases like this.

Quoted 7 lines

)

drivers/usb/serial/io_edgeport.c static void process_rcvd_data(struct edgeport_serial *edge_serial, · line 1826

Quoted 2 lines
drivers/usb/serial/io_edgeport.c +0 -0
 		case EXPECT_DATA: /* Expect data */
 			if (bufferLength < edge_serial->rxBytesRemaining) {

How do you compile test these these patches?

I already explained this above.

Thanks for your comments.
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Gustavo
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maintainer
#3 lore raw
Quoted 27 lines · Gustavo A. R. Silva

Hi Johan,

Quoted 9 lines · Johan Hovold
Quoted 8 lines · Gustavo A. R. Silva

In preparation to enabling -Wimplicit-fallthrough, mark switch cases where we are expecting to fall through.

Signed-off-by Gustavo A. R. Silva <[email protected]>
---
 drivers/usb/serial/io_edgeport.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)
Quoted 14 lines

drivers/usb/serial/io_edgeport.c static void process_rcvd_data(struct edgeport_serial *edge_serial, · line 1763

Quoted 10 lines
drivers/usb/serial/io_edgeport.c +1 -1
index 97c69d3..441dab6 100644
@@ -1760,7 +1760,7 @@ static void process_rcvd_data(struct edgeport_serial *edge_serial,
 				edge_serial->rxState = EXPECT_HDR2;
 				break;
 			}
-			/* otherwise, drop on through */
+			/* else: fall through */

This doesn't silence the compiler warning with gcc 7.2.0 as the "else: " pattern isn't recognised.

Quoted 7 lines

I'm using level 2:

-Wimplicit-fallthrough=2

The thing here is that some people have pointed out that it can be misleading to place a plain fall-through comment after an if-else code block containing a "break". So, the solution above has proved to be a good one.

I don't mind the "else", but I would expect you to mention in the commit message that you're now relying on the non-default warning level (2).

Quoted 16 lines
Quoted 16 lines

drivers/usb/serial/io_edgeport.c static void process_rcvd_data(struct edgeport_serial *edge_serial, · line 1824

Quoted 10 lines
drivers/usb/serial/io_edgeport.c +1 -1
 		case EXPECT_HDR2:
 			edge_serial->rxHeader2 = *buffer;
 			++buffer;

@@ -1820,7 +1820,7 @@ static void process_rcvd_data(struct edgeport_serial *edge_serial,
 					edge_serial->rxState = EXPECT_DATA;
 					break;
 				}
-				/* Else, drop through */
+				/* else: fall through */
 			}

And this doesn't work either due to the "else: " as well as the fact that the compiler expects the fallthrough comment to precede the case statement directly (e.g. it would need to be moved out of the else block, but that isn't necessarily desirable as we discussed last year:

Quoted 7 lines
Quoted 2 lines
	lkml.kernel.org/r/[email protected]

Yes. I'm aware of that. This certainly is still triggering a warning, so I just consider this
as a temporal approach. I still need to define how are we going to manage cases like this.

Ok, so why did you not mention that in the commit message?

If this isn't even addressing the warning you get with the non-default -Wimplicit-fallthrough=2, I don't see this as much of an improvement.

Might as well leave this unchanged, until all warnings in that switch statement are addressed.

Johan
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