linux-kernel - Re: [PATCH 14/19] gpu: drm: selftests: test-drm_dp_mst_helper: Place 'struct drm_dp_sideband_msg_req

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Message-ID: <20201109164004.GZ2063125@dell>
Date:   Mon, 9 Nov 2020 16:40:04 +0000
From:   Lee Jones <lee.jones@...aro.org>
To:     Ville Syrjälä <ville.syrjala@...ux.intel.com>
Cc:     David Airlie <airlied@...ux.ie>,
        David Francis <David.Francis@....com>,
        linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org
Subject: Re: [PATCH 14/19] gpu: drm: selftests: test-drm_dp_mst_helper: Place
 'struct drm_dp_sideband_msg_req_body' onto the heap

On Mon, 09 Nov 2020, Ville Syrjälä wrote:

> On Mon, Nov 09, 2020 at 04:12:58PM +0000, Lee Jones wrote:
> > On Mon, 09 Nov 2020, Ville Syrjälä wrote:
> > 
> > > On Thu, Nov 05, 2020 at 02:45:12PM +0000, Lee Jones wrote:
> > > > The stack is too full.
> > > > 
> > > > Fixes the following W=1 kernel build warning(s):
> > > > 
> > > >  drivers/gpu/drm/selftests/test-drm_dp_mst_helper.c: In function ‘sideband_msg_req_encode_decode’:
> > > >  drivers/gpu/drm/selftests/test-drm_dp_mst_helper.c:161:1: warning: the frame size of 1176 bytes is larger than 1024 bytes [-Wframe-larger-than=]
> > > > 
> > > > Cc: David Airlie <airlied@...ux.ie>
> > > > Cc: Daniel Vetter <daniel@...ll.ch>
> > > > Cc: Lyude Paul <lyude@...hat.com>
> > > > Cc: David Francis <David.Francis@....com>
> > > > Cc: dri-devel@...ts.freedesktop.org
> > > > Signed-off-by: Lee Jones <lee.jones@...aro.org>
> > > > ---
> > > >  .../drm/selftests/test-drm_dp_mst_helper.c    | 29 ++++++++++++-------
> > > >  1 file changed, 18 insertions(+), 11 deletions(-)
> > > > 
> > > > diff --git a/drivers/gpu/drm/selftests/test-drm_dp_mst_helper.c b/drivers/gpu/drm/selftests/test-drm_dp_mst_helper.c
> > > > index 1d696ec001cff..0a539456f6864 100644
> > > > --- a/drivers/gpu/drm/selftests/test-drm_dp_mst_helper.c
> > > > +++ b/drivers/gpu/drm/selftests/test-drm_dp_mst_helper.c
> > > > @@ -120,44 +120,51 @@ sideband_msg_req_equal(const struct drm_dp_sideband_msg_req_body *in,
> > > >  static bool
> > > >  sideband_msg_req_encode_decode(struct drm_dp_sideband_msg_req_body *in)
> > > >  {
> > > > -	struct drm_dp_sideband_msg_req_body out = {0};
> > > > +	struct drm_dp_sideband_msg_req_body *out;
> > > 
> > > How big is it? And why is it that big?
> > 
> > It's a struct of a union of structs.
> > 
> > And it's all allocated on the stack.  Bad news!
> 
> That doesn't answer my questions.

It answers the second question.

The answer to the first question you can `grep` for yourself. ;)

-- 
Lee Jones [李琼斯]
Senior Technical Lead - Developer Services
Linaro.org │ Open source software for Arm SoCs
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