linux-kernel - Re: [PATCH] drm/bochs: Fix NULL dereference on atomic

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Message-ID: <20190311184839.GO2665@phenom.ffwll.local>
Date:   Mon, 11 Mar 2019 19:48:39 +0100
From:   Daniel Vetter <daniel@...ll.ch>
To:     Rodrigo Siqueira <rodrigosiqueiramelo@...il.com>
Cc:     Gerd Hoffmann <kraxel@...hat.com>, David Airlie <airlied@...ux.ie>,
        linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        virtualization@...ts.linux-foundation.org
Subject: Re: [PATCH] drm/bochs: Fix NULL dereference on atomic_disable helper

On Mon, Mar 11, 2019 at 02:49:58PM -0300, Rodrigo Siqueira wrote:
> On 03/11, Gerd Hoffmann wrote:
> >   Hi,
> > 
> > > > IIRC the drm code checks for the atomic_enable callback presence to
> > > > figure whenever it should take the atomic or legacy code paths.
> > > 
> > > It should check for drm_driver->mode_config.funcs.atomic_commit for that,
> > > see drm_drv_uses_atomic_modeset(). Anything else should be a bug.
> > > 
> > > Or do you mean the fallback to the old crtc helper prepare/commit
> > > callbacks?
> > 
> > Probably the later.  There was some reason why I've left in the empty
> > bochs_crtc_atomic_enable() callback ...
> 
> Just for checking before I start to work in this patch:
> The correct solution should be made atomic_enable and atomic_disable
> optional, right? I should do it, and check if Bochs driver really needs
> bochs_crtc_atomic_enable after my change, right?

Yup. I just tried to remember why we haven't done this yet, but I think
that was a patch to make crtc->helper_funcs optional. And that doesn't
make sense imo, since if your crtc doesn't do anything then you don't
really have an atomic driver :-) And if there's ever a legit use case for
this, then that drive probably shouldn't use the atomic helpers ...

But making crtc_helper_funcs->atomic_enable/disable optional sounds like a
good idea.
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch