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

[Carl Vanderlip]

On 1/5/2024 4:38 PM, Dmitry Baryshkov wrote:
> On Sat, 6 Jan 2024 at 02:04, Carl Vanderlip <quic_carlv@xxxxxxxxxxx> 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.

-Carl V.