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

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Date:   Fri, 23 Oct 2020 15:48:49 +0800 (GMT+08:00)
From:   Bernard <bernard@...o.com>
To:     Thomas Zimmermann <tzimmermann@...e.de>
Cc:     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,
        opensource.kernel@...o.com
Subject: Re:Re: [PATCH] gpu/drm/mgag200:remove break after return



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?

BR//Bernard

>Best regards
>Thomas
>
>>  		break;
>>  	}
>>  
>> 
>
>-- 
>Thomas Zimmermann
>Graphics Driver Developer
>SUSE Software Solutions Germany GmbH
>Maxfeldstr. 5, 90409 Nürnberg, Germany
>(HRB 36809, AG Nürnberg)
>Geschäftsführer: Felix Imendörffer