linux-kernel - Re: [PATCH 5/5] gma500: fix a missing break in psb_driver

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Date:   Fri,  1 Apr 2022 19:16:04 +0800
From:   Xiaomeng Tong <xiam0nd.tong@...il.com>
To:     patrik.r.jakobsson@...il.com
Cc:     airlied@...ux.ie, airlied@...hat.com, daniel@...ll.ch,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        xiam0nd.tong@...il.com, yakui.zhao@...el.com
Subject: Re: [PATCH 5/5] gma500: fix a missing break in psb_driver_load

On Fri, 1 Apr 2022 12:10:48 +0200, Patrik Jakobsson wrote:
> On Wed, Mar 30, 2022 at 2:03 PM Xiaomeng Tong <xiam0nd.tong@...il.com> wrote:
> >
> > Instead of exiting the loop as expected when an entry is found, the
> > list_for_each_entry() continues until the traversal is complete. To
> > avoid potential executing 'ret = gma_backlight_init(dev);' repeatly,
> > add a break after the switch statement.
> >
> > Fixes: 5c49fd3aa0ab0 ("gma500: Add the core DRM files and headers")
> > Signed-off-by: Xiaomeng Tong <xiam0nd.tong@...il.com>
> 
> This is incorrect. If we always break on the first iteration we will
> only run gma_backlight_init() if the first connector is LVDS or MIPI.
> This might not be the case and gma_backlight_init() will never run.
> The other loops you have been looking at have an "if (xxx != yyy)
> continue;" statement at the top which skips all the unwanted entries
> but this loop does not.
> 

Yes, your are correct. But it still need to break the loop when found it.
So it is better to add if(!ret) break; after the switch statment.
I will resend another patch if it is necessary.

> > ---
> >  drivers/gpu/drm/gma500/psb_drv.c | 2 ++
> >  1 file changed, 2 insertions(+)
> >
> > diff --git a/drivers/gpu/drm/gma500/psb_drv.c b/drivers/gpu/drm/gma500/psb_drv.c
> > index 65cf1c79dd7c..d65a68811bf7 100644
> > --- a/drivers/gpu/drm/gma500/psb_drv.c
> > +++ b/drivers/gpu/drm/gma500/psb_drv.c
> > @@ -398,6 +398,8 @@ static int psb_driver_load(struct drm_device *dev, unsigned long flags)
> >                         ret = gma_backlight_init(dev);
> >                         break;
> >                 }
> > +
> > +               break;
> >         }
> >
> >         if (ret)
> > --
> > 2.17.1
> >

--
Xiaomeng Tong