Re: [RESEND PATCH v11 02/18] drm: bridge: panel: Add devm_drm_of_dsi_get_bridge helper

From: Maxime Ripard <maxime@cerno.tech>
To: Jagan Teki <jagan@amarulasolutions.com>
Cc: Andrzej Hajda <andrzej.hajda@intel.com>,
	Inki Dae <inki.dae@samsung.com>,
	Marek Szyprowski <m.szyprowski@samsung.com>,
	Joonyoung Shim <jy0922.shim@samsung.com>,
	Seung-Woo Kim <sw0312.kim@samsung.com>,
	Kyungmin Park <kyungmin.park@samsung.com>,
	Frieder Schrempf <frieder.schrempf@kontron.de>,
	Fancy Fang <chen.fang@nxp.com>,
	Tim Harvey <tharvey@gateworks.com>,
	Michael Nazzareno Trimarchi <michael@amarulasolutions.com>,
	Adam Ford <aford173@gmail.com>,
	Neil Armstrong <narmstrong@linaro.org>,
	Robert Foss <robert.foss@linaro.org>,
	Laurent Pinchart <Laurent.pinchart@ideasonboard.com>,
	Tommaso Merciai <tommaso.merciai@amarulasolutions.com>,
	Marek Vasut <marex@denx.de>,
	Matteo Lisi <matteo.lisi@engicam.com>,
	dri-devel@lists.freedesktop.org,
	linux-samsung-soc@vger.kernel.org,
	linux-arm-kernel@lists.infradead.org,
	NXP Linux Team <linux-imx@nxp.com>,
	linux-amarula <linux-amarula@amarulasolutions.com>,
	Linus Walleij <linus.walleij@linaro.org>,
	Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Subject: Re: [RESEND PATCH v11 02/18] drm: bridge: panel: Add devm_drm_of_dsi_get_bridge helper
Date: Mon, 30 Jan 2023 13:56:48 +0100	[thread overview]
Message-ID: <20230130125648.mlrtubymeooejvhg@houat> (raw)
In-Reply-To: <CAMty3ZDTuvYKQYpVnoUU_-b3znJiyR0yBADO-5_5+86KgwYv3Q@mail.gmail.com>

On Fri, Jan 27, 2023 at 11:09:26PM +0530, Jagan Teki wrote:
> Hi,
> 
> On Thu, Jan 26, 2023 at 8:48 PM Jagan Teki <jagan@amarulasolutions.com> wrote:
> >
> > On Thu, Jan 26, 2023 at 5:42 PM Maxime Ripard <maxime@cerno.tech> wrote:
> > >
> > > Hi,
> > >
> > > On Mon, Jan 23, 2023 at 08:41:56PM +0530, Jagan Teki wrote:
> > > > Add devm OF helper to return the next DSI bridge in the chain.
> > > >
> > > > Unlike general bridge return helper devm_drm_of_get_bridge, this
> > > > helper uses the dsi specific panel_or_bridge helper to find the
> > > > next DSI device in the pipeline.
> > > >
> > > > Helper lookup a given child DSI node or a DT node's port and
> > > > endpoint number, find the connected node and return either
> > > > the associated struct drm_panel or drm_bridge device.
> > >
> > > I'm not sure that using a device managed helper is the right choice
> > > here. The bridge will stay longer than the backing device so it will
> > > create a use-after-free. You should probably use a DRM-managed action
> > > here instead.
> >
> > Thanks for the comments. If I understand correctly we can use
> > drmm_panel_bridge_add instead devm_drm_panel_bridge_add once we found
> > the panel or bridge - am I correct?
> 
> Look like it is not possible to use DRM-managed action helper here as
> devm_drm_of_dsi_get_bridge is calling from the DSI host attach hook in
> which we cannot find drm_device pointer (as drm_device pointer is
> mandatory for using DRM-managed action).
> https://github.com/openedev/kernel/blob/imx8mm-dsi-v12/drivers/gpu/drm/bridge/samsung-dsim.c#L1545
> 
> Please check and correct me if I mentioned any incorrect details.

You shouldn't call that function from attach anyway:
https://dri.freedesktop.org/docs/drm/gpu/drm-kms-helpers.html#special-care-with-mipi-dsi-bridges

Maxime

_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel