Re: [PATCH V2 0/3] DSI host and peripheral initialisation ordering

From: Jagan Teki <jagan@amarulasolutions.com>
To: Marek Szyprowski <m.szyprowski@samsung.com>
Cc: Marek Vasut <marex@denx.de>,
	Jernej Skrabec <jernej.skrabec@gmail.com>,
	Thomas Zimmermann <tzimmermann@suse.de>,
	Dave Stevenson <dave.stevenson@raspberrypi.com>,
	David Airlie <airlied@linux.ie>,
	Robert Foss <robert.foss@linaro.org>,
	Jonas Karlman <jonas@kwiboo.se>,
	Douglas Anderson <dianders@chromium.org>,
	Neil Armstrong <narmstrong@baylibre.com>,
	Dmitry Baryshkov <dmitry.baryshkov@linaro.org>,
	Andrzej Hajda <andrzej.hajda@intel.com>,
	DRI Development <dri-devel@lists.freedesktop.org>,
	Andrzej Hajda <andrzej.hajda@gmail.com>,
	Laurent Pinchart <Laurent.pinchart@ideasonboard.com>
Subject: Re: [PATCH V2 0/3] DSI host and peripheral initialisation ordering
Date: Fri, 13 May 2022 19:27:29 +0530	[thread overview]
Message-ID: <CAMty3ZC30i0E5WcpraWNMbArmYPrXiweHTMVz=QoW0_cXh-oTA@mail.gmail.com> (raw)
In-Reply-To: <e96197f9-948a-997e-5453-9f9d179b5f5a@samsung.com>

On Wed, May 11, 2022 at 8:28 PM Marek Szyprowski
<m.szyprowski@samsung.com> wrote:
>
> Hi Dave,
>
> On 05.04.2022 13:43, Dave Stevenson wrote:
> > On Fri, 18 Mar 2022 at 12:25, Dave Stevenson
> > <dave.stevenson@raspberrypi.com>  wrote:
> >> On Fri, 4 Mar 2022 at 15:18, Dave Stevenson
> >> <dave.stevenson@raspberrypi.com>  wrote:
> >>> Hi All
> >> A gentle ping on this series. Any comments on the approach?
> >> Thanks.
> > I realise the merge window has just closed and therefore folks have
> > been busy, but no responses on this after a month?
> >
> > Do I give up and submit a patch to document that DSI is broken and no one cares?
>
> Thanks for pointing this patchset in the 'drm: bridge: Add Samsung MIPI
> DSIM bridge' thread, otherwise I would miss it since I'm not involved
> much in the DRM development.
>
> This resolves most of the issues in the Exynos DSI and its recent
> conversion to the drm bridge framework. I've added the needed
> prepare_upstream_first flags to the panels and everything works fine
> without the bridge chain order hacks.
>
> Feel free to add:
>
> Tested-by: Marek Szyprowski <m.szyprowski@samsung.com>
>
>
> The only remaining thing to resolve is the moment of enabling DSI host.
> The proper sequence is:
>
> 1. host power on, 2. device power on, 3. host init, 4. device init, 5.
> video enable.
>
> #1 is done in dsi's pre_enable, #2 is done in panel's prepare. #3 was so
> far done in the first host transfer call, which usually happens in
> panel's prepare, then the #4 happens. Then video enable is done in the
> enable callbacks.
>
> Jagan wants to move it to the dsi host pre_enable() to let it work with
> DSI bridges controlled over different interfaces
> (https://lore.kernel.org/all/20220504114021.33265-6-jagan@amarulasolutions.com/
> ). This however fails on Exynos with DSI panels, because when dsi's
> pre_enable is called, the dsi device is not yet powered. I've discussed
> this with Andrzej Hajda and we came to the conclusion that this can be
> resolved by adding the init() callback to the struct mipi_dsi_host_ops.
> Then DSI client (next bridge or panel) would call it after powering self
> on, but before sending any DSI commands in its pre_enable/prepare functions.
>
> I've prepared a prototype of such solution. This approach finally
> resolved all the initialization issues! The bridge chain finally matches
> the hardware, no hack are needed, and everything is controlled by the
> DRM core. This prototype also includes the Jagan's patches, which add
> IMX support to Samsung DSIM. If one is interested, here is my git repo
> with all the PoC patches:
>
> https://github.com/mszyprow/linux/tree/v5.18-next-20220511-dsi-rework

This seems a bit confusing to me, how come a Host initialization
depends on the downstream bridge call flow?

Thanks,
Jagan.