Message-Id: <DFW3J1ZV9CXE.2JJTGIA40MU5K@bootlin.com>
Date: Fri, 23 Jan 2026 17:06:41 +0100
From: "Luca Ceresoli" <luca.ceresoli@...tlin.com>
To: "Kory Maincent" <kory.maincent@...tlin.com>
Cc: "Jyri Sarha" <jyri.sarha@....fi>, "Tomi Valkeinen"
 <tomi.valkeinen@...asonboard.com>, "Maarten Lankhorst"
 <maarten.lankhorst@...ux.intel.com>, "Maxime Ripard" <mripard@...nel.org>,
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 Dooley" <conor+dt@...nel.org>, "Russell King" <linux@...linux.org.uk>,
 "Bartosz Golaszewski" <brgl@...ev.pl>, "Tony Lindgren" <tony@...mide.com>,
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Subject: Re: [PATCH v4 18/25] drm/tilcdc: Convert to DRM managed resources

On Thu Jan 22, 2026 at 3:48 PM CET, Kory Maincent wrote:
> On Mon, 19 Jan 2026 22:19:26 +0100
> "Luca Ceresoli" <luca.ceresoli@...tlin.com> wrote:
>
>> On Fri Jan 16, 2026 at 6:02 PM CET, Kory Maincent (TI.com) wrote:
>> > Convert the tilcdc driver to use DRM managed resources (drmm_* APIs)
>> > to eliminate resource lifetime issues, particularly in probe deferral
>> > scenarios.
>> >
>> > This conversion addresses potential use-after-free bugs by ensuring
>> > proper cleanup ordering through the DRM managed resource framework.
>> > The changes include:
>> > - Replace drm_crtc_init_with_planes() with drmm_crtc_alloc_with_planes()
>> > - Replace drm_universal_plane_init() with drmm_universal_plane_alloc()
>> > - Replace drm_simple_encoder_init() with drmm_simple_encoder_alloc()
>> > - Remove manual cleanup in tilcdc_crtc_destroy() and error paths
>> > - Remove drm_encoder_cleanup() from encoder error handling paths
>> > - Use drmm_add_action_or_reset() for remaining cleanup operations
>> >
>> > This approach is recommended by the DRM subsystem for improved resource
>> > lifetime management and is particularly important for drivers that may
>> > experience probe deferral.
>> >
>> > Signed-off-by: Kory Maincent (TI.com) <kory.maincent@...tlin.com>
>> > ---
>> >
>> > Change in v4:
>> > - Newt patch.
>>
>> Why? Adding patches along the way does not help getting your series merged
>> timely. If there's a good reason for adding a new patch, please mention it
>> here.
>
> Thanks for your review.
>
> Sorry for that. The reason is that I faced a null pointer dereference koops if
> for example the panel module is not installed. Then the
> drm_of_find_panel_or_bridge() function return eprobe defer and something goes
> wrong with the DRM resources. Using DRM managed resources solves it.
> I will mention it for the v5.
>
>> > +	tilcdc_crtc = drmm_crtc_alloc_with_planes(dev, struct tilcdc_crtc,
>> > base,
>> > +						  &primary->base,
>> > +						  NULL,
>> > +						  &tilcdc_crtc_funcs,
>> > +						  "tilcdc crtc");
>> > +	if (IS_ERR(tilcdc_crtc)) {
>> > +		dev_err(dev->dev, "Failed to init CRTC: %pe\n",
>> > tilcdc_crtc);
>> > +		return PTR_ERR(tilcdc_crtc);
>> > +	}
>> > +
>> > +	tilcdc_crtc->primary = primary;
>>
>> (*) see below
>>
>> >
>> >  	init_completion(&tilcdc_crtc->palette_loaded);
>> >  	tilcdc_crtc->palette_base = dmam_alloc_coherent(dev->dev,
>> > @@ -978,10 +992,6 @@ int tilcdc_crtc_create(struct drm_device *dev)
>> >
>> >  	crtc = &tilcdc_crtc->base;
>> >
>> > -	ret = tilcdc_plane_init(dev, &tilcdc_crtc->primary);
>> > -	if (ret < 0)
>> > -		goto fail;
>> > -
>> >  	mutex_init(&tilcdc_crtc->enable_lock);
>> >
>> >  	init_waitqueue_head(&tilcdc_crtc->frame_done_wq);
>> > @@ -989,20 +999,12 @@ int tilcdc_crtc_create(struct drm_device *dev)
>> >  	spin_lock_init(&tilcdc_crtc->irq_lock);
>> >  	INIT_WORK(&tilcdc_crtc->recover_work, tilcdc_crtc_recover_work);
>> >
>> > -	ret = drm_crtc_init_with_planes(dev, crtc,
>> > -					&tilcdc_crtc->primary,
>> > -					NULL,
>> > -					&tilcdc_crtc_funcs,
>> > -					"tilcdc crtc");
>> > -	if (ret < 0)
>> > -		goto fail;
>> > -
>> >  	drm_crtc_helper_add(crtc, &tilcdc_crtc_helper_funcs);
>> >
>> > +	ret = drmm_add_action_or_reset(dev, tilcdc_crtc_destroy, priv);
>> > +	if (ret)
>> > +		return ret;
>>
>> Not related to your patch, but if the dmam_alloc_coherent() (not visible in
>> the diff) fails, tilcdc_crtc_destroy() won't be called. Is this intended?
>> At first sight this drmm_add_action_or_reset() should be moved at (*), just
>> after the allocation.
>
> You are totally right.
>
>> However being not related to your patch I'd leave this for another series
>> anyway, to avoid making this series a moving target.
>
> I think it is related to this patch.
> Before this patch there was no need for cleanup as the only action before the
> dmam_alloc_coherent() was a devm_kzalloc().
> Now the plane and the crtc are initialize before the dmam_alloc_coherent() so
> the cleanup need to happen if it fails an error.
>
>> I find this patch hard to read and I think because it is converting
>> multiple things at once. Splitting it in small steps would have been nice,
>> even thought I'm not 100% sure it would have been doable.
>
> Yes, it brought more error when not converting the whole to DRM Managed
> resources in one go.
>
>>
>> Nevertheless it looks correct, so:
>>
>> Reviewed-by: Luca Ceresoli <luca.ceresoli@...tlin.com>
>
> Thanks, but I will remove it due to the small change.
> Or maybe it is ok for you if I keep it with only the move of
> drmm_add_action_or_reset().

If you only move the drmm_add_action_or_reset() where I suggested you can
keep it.

Luca

--
Luca Ceresoli, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com

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