linux-kernel - Re: [PATCH v3 3/4] drm/msm: add a kernel param to select between MDP5 and DPU drivers

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Message-ID: <CAA8EJpqmkzOaewrW8tqSV5wz+0zovZx-kpMdVWp_nW_g1KrRzA@mail.gmail.com>
Date: Mon, 8 Jan 2024 21:07:51 +0200
From: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To: Carl Vanderlip <quic_carlv@...cinc.com>
Cc: Rob Clark <robdclark@...il.com>, Abhinav Kumar <quic_abhinavk@...cinc.com>, 
	Sean Paul <sean@...rly.run>, Marijn Suijten <marijn.suijten@...ainline.org>, 
	David Airlie <airlied@...il.com>, Daniel Vetter <daniel@...ll.ch>, linux-arm-msm@...r.kernel.org, 
	freedreno@...ts.freedesktop.org, linux-kernel@...r.kernel.org, 
	dri-devel@...ts.freedesktop.org, Stephen Boyd <swboyd@...omium.org>
Subject: Re: [PATCH v3 3/4] drm/msm: add a kernel param to select between MDP5
 and DPU drivers

On Mon, 8 Jan 2024 at 19:57, Carl Vanderlip <quic_carlv@...cinc.com> wrote:
>
>
>
> On 1/5/2024 4:38 PM, Dmitry Baryshkov wrote:
> > On Sat, 6 Jan 2024 at 02:04, Carl Vanderlip <quic_carlv@...cinc.com> wrote:
> >>
> >>
> >> On 1/5/2024 3:34 PM, Dmitry Baryshkov wrote:
> >>> diff --git a/drivers/gpu/drm/msm/msm_drv.c b/drivers/gpu/drm/msm/msm_drv.c
> >>> index 50b65ffc24b1..ef57586fbeca 100644
> >>> --- a/drivers/gpu/drm/msm/msm_drv.c
> >>> +++ b/drivers/gpu/drm/msm/msm_drv.c
> >>> @@ -969,6 +969,37 @@ static int add_components_mdp(struct device *master_dev,
> >>>        return 0;
> >>>    }
> >>>
> >>> +#if !IS_REACHABLE(CONFIG_DRM_MSM_MDP5) || !IS_REACHABLE(CONFIG_DRM_MSM_DPU)
> >>> +bool msm_disp_drv_should_bind(struct device *dev, bool mdp5_driver)
> >>> +{
> >>> +     /* If just a single driver is enabled, use it no matter what */
> >>> +     return true;
> >>> +}
> >>
> >> This will cause both MDP/DPU probes to return -ENODEV, rather than
> >> select the enabled one.
> >
> > No. The code (e.g. for DPU) is:
> >
> >         if (!msm_disp_drv_should_bind(&pdev->dev, true))
> >                  return -ENODEV;
> >
> > So the driver returns -ENODEV if msm_disp_drv_should_bind() returns
> > false. Which is logical from the function name point of view.
> >
>
> but msm_disp_drv_should_bind() is returning true in the #if !REACHABLE()
> case?
>
> at minimum the comment is incorrect since returning true causes the
> driver to NOT be used.

No. Returning _false_ causes the driver to not be used.

-- 
With best wishes
Dmitry