linux-kernel - Re: [PATCH v2 02/22] drm: Add valid clones check

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Message-ID: <Z2A4uahCHuOz45Fc@phenom.ffwll.local>
Date: Mon, 16 Dec 2024 15:27:05 +0100
From: Simona Vetter <simona.vetter@...ll.ch>
To: Abhinav Kumar <quic_abhinavk@...cinc.com>
Cc: Jessica Zhang <quic_jesszhan@...cinc.com>,
	Maxime Ripard <mripard@...nel.org>, Rob Clark <robdclark@...il.com>,
	Dmitry Baryshkov <dmitry.baryshkov@...aro.org>,
	Sean Paul <sean@...rly.run>,
	Marijn Suijten <marijn.suijten@...ainline.org>,
	David Airlie <airlied@...il.com>, Daniel Vetter <daniel@...ll.ch>,
	Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
	Thomas Zimmermann <tzimmermann@...e.de>, quic_ebharadw@...cinc.com,
	linux-arm-msm@...r.kernel.org, dri-devel@...ts.freedesktop.org,
	freedreno@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
	Rob Clark <robdclark@...omium.org>,
	Ville Syrjälä <ville.syrjala@...ux.intel.com>
Subject: Re: [PATCH v2 02/22] drm: Add valid clones check

On Sun, Dec 15, 2024 at 06:19:08PM -0800, Abhinav Kumar wrote:
> Hi Maxime
> 
> Gentle reminder on this one.
> 
> We are looking for some advice on how to go about KUnit for this static
> function.
> 
> Please help with our question below.
> 
> Thanks
> 
> Abhinav
> 
> On 12/6/2024 4:48 PM, Jessica Zhang wrote:
> > 
> > 
> > On 9/25/2024 12:23 AM, Maxime Ripard wrote:
> > > On Tue, Sep 24, 2024 at 03:59:18PM GMT, Jessica Zhang wrote:
> > > > Check that all encoders attached to a given CRTC are valid
> > > > possible_clones of each other.
> > > > 
> > > > Signed-off-by: Jessica Zhang <quic_jesszhan@...cinc.com>
> > > > ---
> > > >   drivers/gpu/drm/drm_atomic_helper.c | 23 +++++++++++++++++++++++
> > > >   1 file changed, 23 insertions(+)
> > > > 
> > > > diff --git a/drivers/gpu/drm/drm_atomic_helper.c
> > > > b/drivers/gpu/drm/drm_atomic_helper.c
> > > > index 43cdf39019a4..cc4001804fdc 100644
> > > > --- a/drivers/gpu/drm/drm_atomic_helper.c
> > > > +++ b/drivers/gpu/drm/drm_atomic_helper.c
> > > > @@ -574,6 +574,25 @@ mode_valid(struct drm_atomic_state *state)
> > > >       return 0;
> > > >   }
> > > > +static int drm_atomic_check_valid_clones(struct
> > > > drm_atomic_state *state,
> > > > +                     struct drm_crtc *crtc)
> > > > +{
> > > > +    struct drm_encoder *drm_enc;
> > > > +    struct drm_crtc_state *crtc_state =
> > > > drm_atomic_get_new_crtc_state(state,
> > > > +                                      crtc);
> > > > +
> > > > +    drm_for_each_encoder_mask(drm_enc, crtc->dev,
> > > > crtc_state->encoder_mask) {
> > > > +        if ((crtc_state->encoder_mask & drm_enc->possible_clones) !=
> > > > +            crtc_state->encoder_mask) {
> > > > +            DRM_DEBUG("crtc%d failed valid clone check for mask
> > > > 0x%x\n",
> > > > +                  crtc->base.id, crtc_state->encoder_mask);
> > > > +            return -EINVAL;
> > > > +        }
> > > > +    }
> > > > +
> > > > +    return 0;
> > > > +}
> > > > +
> > > >   /**
> > > >    * drm_atomic_helper_check_modeset - validate state object for
> > > > modeset changes
> > > >    * @dev: DRM device
> > > > @@ -745,6 +764,10 @@ drm_atomic_helper_check_modeset(struct
> > > > drm_device *dev,
> > > >           ret = drm_atomic_add_affected_planes(state, crtc);
> > > >           if (ret != 0)
> > > >               return ret;
> > > > +
> > > > +        ret = drm_atomic_check_valid_clones(state, crtc);
> > > > +        if (ret != 0)
> > > > +            return ret;
> > > >       }
> > > 
> > > Pretty much the same comment, we should have kunit tests for this.
> > 
> > Hey Maxime,
> > 
> > I'm working on the kunit test for this and had a question on the design
> > for the unit test:
> > 
> > Since this is a static helper that returns a pretty common error code,
> > how would you recommend going about making sure that
> > `drm_atomic_check_valid_clones()` specifically is returning the error
> > (and not a different part of check_modeset) when testing the
> > check_valid_clones() failure path?

So the usual way to test very specific things of a big function is to
first setup a driver and atomic request which does pass all checks. And
then do a minimal change which does not pass anymore.

So what you could do here is have 3 connectors 1 crtc, but only the first
two connectors can be cloned. Then do an atomic request with those two
connectors and the crtc. Then the 2nd request is with one of the
connectors replaced with the 3rd one (so it's still a clone config, but
not an invalid one), then have a failure.

Note: I didn't check all the details, I might be getting something wrong
here, but the idea should work.

Cheers, Sima

> > 
> > Thanks,
> > 
> > Jessica Zhang
> > 
> > > 
> > > Maxime
> > 

-- 
Simona Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch