Hi Bernard.
On Fri, Oct 23, 2020 at 03:48:49PM +0800, Bernard wrote:
>
>
> From: Thomas Zimmermann <tzimmermann@xxxxxxx>
> Date: 2020-10-23 15:13:30
> To: Bernard Zhao <bernard@xxxxxxxx>,Dave Airlie <airlied@xxxxxxxxxx>,David Airlie <airlied@xxxxxxxx>,Daniel Vetter <daniel@xxxxxxxx>,dri-devel@xxxxxxxxxxxxxxxxxxxxx,linux-kernel@xxxxxxxxxxxxxxx
> Cc: opensource.kernel@xxxxxxxx
> 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@xxxxxxxx>
> >> ---
> >> 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.
Sam
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