linux-kernel - Re: [PATCH][next] greybus: Use fallthrough pseudo-keyword

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Date:   Tue, 28 Jul 2020 17:37:05 -0500
From:   Alex Elder <elder@...e.org>
To:     "Gustavo A. R. Silva" <gustavoars@...nel.org>,
        Johan Hovold <johan@...nel.org>, Alex Elder <elder@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     greybus-dev@...ts.linaro.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH][next] greybus: Use fallthrough pseudo-keyword

On 7/27/20 1:32 PM, Gustavo A. R. Silva wrote:
> Replace the existing /* fall through */ comments and its variants with
> the new pseudo-keyword macro fallthrough[1].
> 
> [1] https://www.kernel.org/doc/html/v5.7/process/deprecated.html?highlight=fallthrough#implicit-switch-case-fall-through

Thanks for the patch.  It looks good, but it raises
another question I'd like discussion on.

It seems that Johan likes default (or final) cases in
switch statements without a "break" statement.  Viresh
and Bryan appear to be fond of this too.

It's pedantic, but I don't like that.  Am I wrong?
   --> Johan/Viresh/Bryan would you please comment?

If they aren't convincing (or don't care) I think break
statements should also be added here:
- In gb_interface_read_and_clear_init_status() for the
   default case
- In gb_interface_activate() for the default case.
- In gb_svc_process_deferred_request() for the default
   case

But let's wait to see what Johan (et al) says.  If you
don't want to do that, say so and I'll do it later.

I looked at the code in drivers/staging/greybus/ and saw
no need to add a "fallthrough" anywhere, but:
- In fw_mgmt_backend_fw_version_operation() Viresh
   seems to have skipped the break in the fault statement
- In gb_uart_request_handler() Bryan did this too.

Depending on discussion, these could be fixed in a
separate patch as well.

These cases aren't found by "checkpatch.pl" because it only
looks at case "blocks" that are followed by another case.
So the last case isn't checked.

					-Alex

> Signed-off-by: Gustavo A. R. Silva <gustavoars@...nel.org>
> ---
>   drivers/greybus/es2.c       | 2 +-
>   drivers/greybus/interface.c | 2 +-
>   2 files changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/greybus/es2.c b/drivers/greybus/es2.c
> index 366716f11b1a..1df6ab5d339d 100644
> --- a/drivers/greybus/es2.c
> +++ b/drivers/greybus/es2.c
> @@ -759,7 +759,7 @@ static int check_urb_status(struct urb *urb)
>   	case -EOVERFLOW:
>   		dev_err(dev, "%s: overflow actual length is %d\n",
>   			__func__, urb->actual_length);
> -		/* fall through */
> +		fallthrough;
>   	case -ECONNRESET:
>   	case -ENOENT:
>   	case -ESHUTDOWN:
> diff --git a/drivers/greybus/interface.c b/drivers/greybus/interface.c
> index 67dbe6fda9a1..58ea374d8aaa 100644
> --- a/drivers/greybus/interface.c
> +++ b/drivers/greybus/interface.c
> @@ -1233,7 +1233,7 @@ int gb_interface_add(struct gb_interface *intf)
>   	case GB_INTERFACE_TYPE_GREYBUS:
>   		dev_info(&intf->dev, "GMP VID=0x%08x, PID=0x%08x\n",
>   			 intf->vendor_id, intf->product_id);
> -		/* fall-through */
> +		fallthrough;
>   	case GB_INTERFACE_TYPE_UNIPRO:
>   		dev_info(&intf->dev, "DDBL1 Manufacturer=0x%08x, Product=0x%08x\n",
>   			 intf->ddbl1_manufacturer_id,
>