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From: Jagan Teki <jagan@amarulasolutions.com>
To: "a.hajda" <a.hajda@samsung.com>
Cc: Maxime Ripard <maxime@cerno.tech>,
	Sam Ravnborg <sam@ravnborg.org>,
	Daniel Vetter <daniel.vetter@intel.com>,
	David Airlie <airlied@linux.ie>,
	Thierry Reding <thierry.reding@gmail.com>,
	Laurent Pinchart <Laurent.pinchart@ideasonboard.com>,
	Maarten Lankhorst <maarten.lankhorst@linux.intel.com>,
	Thomas Zimmermann <tzimmermann@suse.de>,
	Jernej Skrabec <jernej.skrabec@gmail.com>,
	Neil Armstrong <narmstrong@baylibre.com>,
	Jonas Karlman <jonas@kwiboo.se>,
	Robert Foss <robert.foss@linaro.org>,
	linux-kernel <linux-kernel@vger.kernel.org>,
	dri-devel <dri-devel@lists.freedesktop.org>
Subject: Re: [PATCH v2 0/8] drm/bridge: Make panel and bridge probe order consistent
Date: Mon, 9 Aug 2021 13:30:05 +0530	[thread overview]
Message-ID: <CAMty3ZDLM0Ap4Ni+kExEgVyFw2eQygZNeTxbWjOxvE=uduVkag@mail.gmail.com> (raw)
In-Reply-To: <cc638e20-aa7c-7014-f70b-1bb68e629d87@samsung.com>

Hi Andrzej,

On Wed, Aug 4, 2021 at 7:48 PM a.hajda <a.hajda@samsung.com> wrote:
>
> Hi Maxime,
>
> I have been busy with other tasks, and I did not follow the list last
> time, so sorry for my late response.
>
> On 28.07.2021 15:32, Maxime Ripard wrote:
> > Hi,
> >
> > We've encountered an issue with the RaspberryPi DSI panel that prevented the
> > whole display driver from probing.
> >
> > The issue is described in detail in the commit 7213246a803f ("drm/vc4: dsi:
> > Only register our component once a DSI device is attached"), but the basic idea
> > is that since the panel is probed through i2c, there's no synchronization
> > between its probe and the registration of the MIPI-DSI host it's attached to.
> >
> > We initially moved the component framework registration to the MIPI-DSI Host
> > attach hook to make sure we register our component only when we have a DSI
> > device attached to our MIPI-DSI host, and then use lookup our DSI device in our
> > bind hook.
> >
> > However, all the DSI bridges controlled through i2c are only registering their
> > associated DSI device in their bridge attach hook, meaning with our change
>
>
> I guess this is incorrect. I have promoted several times the pattern
> that device driver shouldn't expose its interfaces (for example
> component_add, drm_panel_add, drm_bridge_add) until it gathers all
> required dependencies. In this particular case bridges should defer
> probe until DSI bus becomes available. I guess this way the patch you
> reverts would work.
>
> I advised few times this pattern in case of DSI hosts, apparently I
> didn't notice the similar issue can appear in case of bridges. Or there
> is something I have missed???

Look like Maxime is correct. I2C based DSI bridge will get probe
during bridge_attach which usually called from bridge driver
bridge_attach call. Non-I2C bridges and DSI panels will get probe
during host.attach.

We do get similar situation for dw-mipi-dsi bridges, where icn6211
bridge is not I2C-based bridge and it gets probed in host_attach and
sn65dsi83 is I2C based bridge and it gets probed in bridge_attach.

Here is the simple call trace we have observed with dw-mipi-dsi bridge
when all possible DSI device are trying to probe.

1. DSI panels and bridges will invoke the host attach
   from probe in order to find the panel_or_bridge.

   chipone_probe()
       dw_mipi_dsi_host_attach().start
           dw_mipi_dsi_panel_or_bridge()
                ...found the panel_or_bridge...

   ltdc_encoder_init().start
       dw_mipi_dsi_bridge_attach().start
                   dw_mipi_dsi_host_attach().start
                       chipone_attach(). start

                       chipone_attach(). done
                   dw_mipi_dsi_host_attach().done
       dw_mipi_dsi_bridge_attach(). done
   ltdc_encoder_init().done

2. I2C based DSI bridge will invoke the drm_bridge_attach
   from bridge attach in order to find the panel_or_bridge.

   ltdc_encoder_init().start
       dw_mipi_dsi_bridge_attach().start
           dw_mipi_dsi_panel_or_bridge()
                ...found the panel_or_bridge...
                   dw_mipi_dsi_host_attach().start
                       sn65dsi83_attach(). start

                       sn65dsi83_attach(). done
                   dw_mipi_dsi_host_attach().done
       dw_mipi_dsi_bridge_attach(). done
   ltdc_encoder_init().done

It is correct that the I2C-based bridges will attach the host via
mipi_dsi_attach in driver bridge API where as it done in probe for
Non-I2C bridges and DSI panels.

>
> Anyway there are already eleven(?) bridge drivers using this pattern. I
> wonder if fixing it would be difficult, or if it expose other issues???
> The patches should be quite straightforward - move
> of_find_mipi_dsi_host_by_node and mipi_dsi_device_register_full to probe
> time.
>
> Finally I think that if we will not fix these bridge drivers we will
> encounter another set of issues with new platforms connecting "DSI host
> drivers assuming this pattern" and "i2c/dsi device drivers assuming
> pattern already present in the bridges".

Agreed, I'm trying to understand the several ways to fix this. Right
now I'm trying this on sun6i_mipi_dsi and exynos_drm_dsi. Will let you
know for any update and suggestions on the same.

Thanks,
Jagan.

  reply	other threads:[~2021-08-09  8:00 UTC|newest]

Thread overview: 13+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-07-28 13:32 Maxime Ripard
2021-07-28 13:32 ` [PATCH v2 1/8] Revert "drm/vc4: dsi: Only register our component once a DSI device is attached" Maxime Ripard
2021-07-28 13:32 ` [PATCH v2 2/8] drm/bridge: Add a function to abstract away panels Maxime Ripard
2021-07-28 13:32 ` [PATCH v2 3/8] drm/bridge: Add documentation sections Maxime Ripard
2021-07-28 13:32 ` [PATCH v2 4/8] drm/bridge: Document the probe issue with MIPI-DSI bridges Maxime Ripard
2021-07-28 13:32 ` [PATCH v2 5/8] drm/panel: Create attach and detach callbacks Maxime Ripard
2021-07-28 13:32 ` [PATCH v2 6/8] drm/vc4: dsi: Switch to drm_of_get_bridge Maxime Ripard
2021-07-28 13:32 ` [PATCH v2 7/8] drm/panel: raspberrypi-touchscreen: Use the attach hook Maxime Ripard
2021-07-28 13:32 ` [PATCH v2 8/8] drm/panel: raspberrypi-touchscreen: Remove MIPI-DSI driver Maxime Ripard
     [not found] ` <CGME20210804140941eucas1p2d4d4ec491074530c714797523aec05ea@eucas1p2.samsung.com>
2021-08-04 14:09   ` [PATCH v2 0/8] drm/bridge: Make panel and bridge probe order consistent a.hajda
2021-08-09  8:00     ` Jagan Teki [this message]
2021-08-09 12:03       ` Andrzej Hajda
2021-08-20 16:49     ` Maxime Ripard

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