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

[Jagan Teki <jagan@amarulasolutions.com>]

Hi Marek,

On Wed, May 18, 2022 at 7:35 PM Marek Szyprowski
<m.szyprowski@samsung.com> wrote:
>
> Hi Dave,
>
> On 11.05.2022 17:47, Dave Stevenson wrote:
> > On Wed, 11 May 2022 at 15:58, Marek Szyprowski <m.szyprowski@samsung.com> wrote:
> >> 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>
> > Thanks for testing it. I was almost at the stage of abandoning the patch set.
> >
> >> 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.
> > What's your definition of host power on and host init here? What state
> > are you defining the DSI interface to be in after each operation?
>
> Well, lets start from the point that I'm not a DSI specialist nor I'm
> not the exynos-dsi author. I just played a bit with the code trying to
> restore proper driver operation on the various Exynos based boards I have.
>
> By the host/device power on I mean enabling their power regulators. By
> host init I mean executing the samsung_dsim_init() function, which
> basically sets the lp-11 state if I understand it right.
>
>
> >> 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/
> >> ).
> > I think I'm in agreement with Jagan.
> > As documented in patch 4/4:
> > + * A DSI host should keep the PHY powered down until the pre_enable
> > operation is
> > + * called. All lanes are in an undefined idle state up to this point, and it
> > + * must not be assumed that it is LP-11.
> > + * pre_enable should initialise the PHY, set the data lanes to LP-11, and the
> > + * clock lane to either LP-11 or HS depending on the mode_flag
> > + * %MIPI_DSI_CLOCK_NON_CONTINUOUS.
>
> Right, this theory makes sense.
>
> However Exynos DSI for some reasons did the host initialization in the
> first call of the samsung_dsim_host_transfer(). If I moved the host
> initialization to pre_enable (before powering the panel on), executing
> DSI commands failed (timeout). This issue happens on all boards I have
> access (Trats, Trats2, Arndale, TM2e), so this must be an issue with
> Exynos DSI host itself not related to particular panel/bridge.
>
> If I call samsung_dsim_init() once again, before issuing the first DSI
> command, then everything works fine. I've tried to check which part of
> that function is needed to be executed before transferring the commands,
> but it turned out that the complete host reset and (re)configuration is
> necessary. It looks that the initialization will need to be done twice,
> first time in the pre_enable to satisfy Jagan case, then on the first
> dsi transfer to make it work with real DSI panels.
>
> Here is a git repo with such change:
> https://github.com/mszyprow/linux/tree/v5.18-next-20220511-dsi-rework-v2

This is worthy check, I will test it on imx8mm and integrate it into
the next version - hope this is fine for you?

Jagan.