linux-kernel - Re: [PATCH] drm/msm: Make .remove and .shutdown HW shutdown consistent

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Message-ID: <7dc80ce9-83d5-2dc2-f660-fb8f6162c893@redhat.com>
Date:   Sun, 24 Jul 2022 11:06:23 +0200
From:   Javier Martinez Canillas <javierm@...hat.com>
To:     Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
Cc:     linux-kernel@...r.kernel.org,
        Abhinav Kumar <quic_abhinavk@...cinc.com>,
        Daniel Vetter <daniel@...ll.ch>,
        David Airlie <airlied@...ux.ie>,
        Rob Clark <robdclark@...il.com>, Sean Paul <sean@...rly.run>,
        dri-devel@...ts.freedesktop.org, freedreno@...ts.freedesktop.org,
        linux-arm-msm@...r.kernel.org
Subject: Re: [PATCH] drm/msm: Make .remove and .shutdown HW shutdown
 consistent

On 7/24/22 10:53, Dmitry Baryshkov wrote:
> On Sun, 24 Jul 2022 at 00:09, Javier Martinez Canillas

[...]

>> -
>>         /*
>>          * Shutdown the hw if we're far enough along where things might be on.
>>          * If we run this too early, we'll end up panicking in any variety of
>> @@ -205,10 +199,21 @@ static int msm_drm_uninit(struct device *dev)
>>          * msm_drm_init, drm_dev->registered is used as an indicator that the
>>          * shutdown will be successful.
>>          */
>> -       if (ddev->registered) {
>> +       if (dev->registered)
>> +               drm_atomic_helper_shutdown(dev);
>> +}
>> +
>> +static int msm_drm_uninit(struct device *dev)
>> +{
>> +       struct platform_device *pdev = to_platform_device(dev);
>> +       struct msm_drm_private *priv = platform_get_drvdata(pdev);
>> +       struct drm_device *ddev = priv->dev;
>> +       struct msm_kms *kms = priv->kms;
>> +       int i;
>> +
>> +       if (ddev->registered)
>>                 drm_dev_unregister(ddev);
> 
> No. The drm_dev_unregister() should come before drm_atomic_helper_shutdown().
>

I'm not sure to understand what you meant here, since drm_dev_unregister() is
called before drm_atomic_helper_shutdown() that's called in msm_shutdown_hw().
 
> Also drm_dev_unregister() should not be a part of .shutdown callback.
> See the documentation in the drm_drv.c
>

It is not right now, msm_shutdown_hw() only calls drm_atomic_helper_shutdown()
but drm_dev_unregister() is still called from the msm_drm_uninit() function.
 
Now, your comment made me realize that there's a bug in this patch since after
the drm_dev_unregister(), dev->registered will be set to false and so in the
.remove -> .unbind path drm_atomic_helper_shutdown() will never be executed.

I guess one option is to do the if (dev->registered) check in the callers but
then it won't really be worth it to have a helper and we could just add that
check in msm_drv_shutdown() to conditionally call drm_atomic_helper_shutdown().

-- 
Best regards,

Javier Martinez Canillas
Linux Engineering
Red Hat