linux-kernel - Re:Re: Re: [PATCH] gpu/drm/mgag200:remove break after return

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Date:   Tue, 27 Oct 2020 20:05:37 +0800 (GMT+08:00)
From:   Bernard <bernard@...o.com>
To:     Sam Ravnborg <sam@...nborg.org>
Cc:     Thomas Zimmermann <tzimmermann@...e.de>,
        opensource.kernel@...o.com, David Airlie <airlied@...ux.ie>,
        linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        Dave Airlie <airlied@...hat.com>
Subject: Re:Re: Re: [PATCH] gpu/drm/mgag200:remove break after return


From: Sam Ravnborg <sam@...nborg.org>
Date: 2020-10-25 01:14:57
To:  Bernard <bernard@...o.com>
Cc:  Thomas Zimmermann <tzimmermann@...e.de>,opensource.kernel@...o.com,David Airlie <airlied@...ux.ie>,linux-kernel@...r.kernel.org,dri-devel@...ts.freedesktop.org,Dave Airlie <airlied@...hat.com>
Subject: Re: Re: [PATCH] gpu/drm/mgag200:remove break after return>Hi Bernard.
>
>On Fri, Oct 23, 2020 at 03:48:49PM +0800, Bernard wrote:
>> 
>> 
>> From: Thomas Zimmermann <tzimmermann@...e.de>
>> Date: 2020-10-23 15:13:30
>> To:  Bernard Zhao <bernard@...o.com>,Dave Airlie <airlied@...hat.com>,David Airlie <airlied@...ux.ie>,Daniel Vetter <daniel@...ll.ch>,dri-devel@...ts.freedesktop.org,linux-kernel@...r.kernel.org
>> Cc:  opensource.kernel@...o.com
>> Subject: Re: [PATCH] gpu/drm/mgag200:remove break after return>Hi
>> >
>> >On 23.10.20 09:00, Bernard Zhao wrote:
>> >> In function mgag200_set_pci_regs, there are some switch cases
>> >> returned, then break. These break will never run.
>> >> This patch is to make the code a bit readable.
>> >> 
>> >> Signed-off-by: Bernard Zhao <bernard@...o.com>
>> >> ---
>> >>  drivers/gpu/drm/mgag200/mgag200_mode.c | 5 +----
>> >>  1 file changed, 1 insertion(+), 4 deletions(-)
>> >> 
>> >> diff --git a/drivers/gpu/drm/mgag200/mgag200_mode.c b/drivers/gpu/drm/mgag200/mgag200_mode.c
>> >> index 38672f9e5c4f..de873a5d276e 100644
>> >> --- a/drivers/gpu/drm/mgag200/mgag200_mode.c
>> >> +++ b/drivers/gpu/drm/mgag200/mgag200_mode.c
>> >> @@ -794,20 +794,17 @@ static int mgag200_crtc_set_plls(struct mga_device *mdev, long clock)
>> >>  	case G200_SE_A:
>> >>  	case G200_SE_B:
>> >>  		return mga_g200se_set_plls(mdev, clock);
>> >> -		break;
>> >>  	case G200_WB:
>> >>  	case G200_EW3:
>> >>  		return mga_g200wb_set_plls(mdev, clock);
>> >> -		break;
>> >>  	case G200_EV:
>> >>  		return mga_g200ev_set_plls(mdev, clock);
>> >> -		break;
>> >>  	case G200_EH:
>> >>  	case G200_EH3:
>> >>  		return mga_g200eh_set_plls(mdev, clock);
>> >> -		break;
>> >>  	case G200_ER:
>> >>  		return mga_g200er_set_plls(mdev, clock);
>> >> +	default:
>> >
>> >No default case here. If one of the enum values is not handled by the
>> >switch, the compiler should warn about it.
>> 
>> Hi
>> 
>> For this point I was a little confused, about this switch variable "mdev->type", my understanding is that this variable`s value can be certain only when the code is running.
>> How does the compiler warn this("If one of the enum values is not handled") before the code runs?
>
>If the switch/case does not include "G200_ER" then the compiler can see
>one enum value is missing from the list and can warn.
>As a test - Try to drop the default and drop G200_ER - then the
>compiler (hopefully) will warn.

Hi, Sam & Thomas：

  Thank you very much for your kind comments, I learned new useful knowledge.
  I will resubmit the patch.

BR//Bernard

>	Sam