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Date: Mon, 22 Apr 2024 01:35:03 +0300
From: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
To: Abhinav Kumar <quic_abhinavk@quicinc.com>
Cc: Rob Clark <robdclark@gmail.com>, Sean Paul <sean@poorly.run>, 
	Marijn Suijten <marijn.suijten@somainline.org>, David Airlie <airlied@gmail.com>, 
	Daniel Vetter <daniel@ffwll.ch>, linux-arm-msm@vger.kernel.org, dri-devel@lists.freedesktop.org, 
	freedreno@lists.freedesktop.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 1/3] drm/msm: don't clean up priv->kms prematurely
Message-ID: <n7eet54g72usmuh4hdz6yce3i4ieweu4orgd7gewu7y53ejucc@dzmq2a2wdxkc>
References: <20240420-mdp4-fixes-v1-0-96a70f64fa85@linaro.org>
 <20240420-mdp4-fixes-v1-1-96a70f64fa85@linaro.org>
 <67fbd629-3e80-b706-83a3-7baff3efd6c1@quicinc.com>
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In-Reply-To: <67fbd629-3e80-b706-83a3-7baff3efd6c1@quicinc.com>

On Sat, Apr 20, 2024 at 04:02:00PM -0700, Abhinav Kumar wrote:
> 
> 
> On 4/19/2024 7:33 PM, Dmitry Baryshkov wrote:
> > MSM display drivers provide kms structure allocated during probe().
> > Don't clean up priv->kms field in case of an error. Otherwise probe
> > functions might fail after KMS probe deferral.
> > 
> 
> So just to understand this more, this will happen when master component
> probe (dpu) succeeded but other sub-component probe (dsi) deferred?
> 
> Because if master component probe itself deferred it will allocate priv->kms
> again isnt it and we will not even hit here.

Master probing succeeds (so priv->kms is set), then kms_init fails at
runtime, during binding of the master device. This results in probe
deferral from the last component's component_add() function and reprobe
attempt when possible (once the next device is added or probed). However
as priv->kms is NULL, probe crashes.

> 
> > Fixes: a2ab5d5bb6b1 ("drm/msm: allow passing struct msm_kms to msm_drv_probe()")
> > Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
> > ---
> >   drivers/gpu/drm/msm/msm_kms.c | 1 -
> >   1 file changed, 1 deletion(-)
> > 
> > diff --git a/drivers/gpu/drm/msm/msm_kms.c b/drivers/gpu/drm/msm/msm_kms.c
> > index af6a6fcb1173..6749f0fbca96 100644
> > --- a/drivers/gpu/drm/msm/msm_kms.c
> > +++ b/drivers/gpu/drm/msm/msm_kms.c
> > @@ -244,7 +244,6 @@ int msm_drm_kms_init(struct device *dev, const struct drm_driver *drv)
> >   	ret = priv->kms_init(ddev);
> >   	if (ret) {
> >   		DRM_DEV_ERROR(dev, "failed to load kms\n");
> > -		priv->kms = NULL;
> >   		return ret;
> >   	}
> > 

-- 
With best wishes
Dmitry