Message-ID: <20230829080348.GH17387@pengutronix.de>
Date:   Tue, 29 Aug 2023 10:03:48 +0200
From:   Michael Tretter <m.tretter@...gutronix.de>
To:     Adam Ford <aford173@...il.com>
Cc:     Inki Dae <inki.dae@...sung.com>,
        Jagan Teki <jagan@...rulasolutions.com>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        Andrzej Hajda <andrzej.hajda@...el.com>,
        Neil Armstrong <neil.armstrong@...aro.org>,
        Robert Foss <rfoss@...nel.org>,
        Laurent Pinchart <Laurent.pinchart@...asonboard.com>,
        Jonas Karlman <jonas@...boo.se>,
        Jernej Skrabec <jernej.skrabec@...il.com>,
        David Airlie <airlied@...il.com>,
        Daniel Vetter <daniel@...ll.ch>, kernel@...gutronix.de,
        Marco Felsch <m.felsch@...gutronix.de>,
        linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org
Subject: Re: [PATCH 0/5] drm/bridge: samsung-dsim: fix various modes with
 ADV7535 bridge

On Mon, 28 Aug 2023 18:07:08 -0500, Adam Ford wrote:
> On Mon, Aug 28, 2023 at 11:13 AM Adam Ford <aford173@...il.com> wrote:
> >
> > On Mon, Aug 28, 2023 at 10:59 AM Michael Tretter
> > <m.tretter@...gutronix.de> wrote:
> > >
> > > I tested the i.MX8M Nano EVK with the NXP supplied MIPI-DSI adapter,
> > > which uses an ADV7535 MIPI-DSI to HDMI converter. I found that a few
> > > modes were working, but in many modes my monitor stayed dark.
> > >
> > > This series fixes the Samsung DSIM bridge driver to bring up a few more
> > > modes:
> > >
> > > The driver read the rate of the PLL ref clock only during probe.
> > > However, if the clock is re-parented to the VIDEO_PLL, changes to the
> > > pixel clock have an effect on the PLL ref clock. Therefore, the driver
> > > must read and potentially update the PLL ref clock on every modeset.
> > >
> > > I also found that the rounding mode of the porches and active area has
> > > an effect on the working modes. If the driver rounds up instead of
> > > rounding down and be calculates them in Hz instead of kHz, more modes
> > > start to work.
> > >
> > > The following table shows the modes that were working in my test without
> > > this patch set and the modes that are working now:
> > >
> > > |            Mode | Before | Now |
> > > | 1920x1080-60.00 | X      | X   |
> > > | 1920x1080-59.94 |        | X   |
> > > | 1920x1080-50.00 |        | X   |
> > > | 1920x1080-30.00 |        | X   |
> > > | 1920x1080-29.97 |        | X   |
> > > | 1920x1080-25.00 |        | X   |
> > > | 1920x1080-24.00 |        |     |
> > > | 1920x1080-23.98 |        |     |
> > > | 1680x1050-59.88 |        | X   |
> > > | 1280x1024-75.03 | X      | X   |
> > > | 1280x1024-60.02 | X      | X   |
> > > |  1200x960-59.99 |        | X   |
> > > |  1152x864-75.00 | X      | X   |
> > > |  1280x720-60.00 |        |     |
> > > |  1280x720-59.94 |        |     |
> > > |  1280x720-50.00 |        | X   |
> > > |  1024x768-75.03 |        | X   |
> > > |  1024x768-60.00 |        | X   |
> > > |   800x600-75.00 | X      | X   |
> > > |   800x600-60.32 | X      | X   |
> > > |   720x576-50.00 | X      | X   |
> > > |   720x480-60.00 |        |     |
> > > |   720x480-59.94 | X      |     |
> > > |   640x480-75.00 | X      | X   |
> > > |   640x480-60.00 |        | X   |
> > > |   640x480-59.94 |        | X   |
> > > |   720x400-70.08 |        |     |
> > >
> >
> > Nice!
> >
> > > Interestingly, the 720x480-59.94 mode stopped working. However, I am
> > > able to bring up the 720x480 modes by manually hacking the active area
> > > (hsa) to 40 and carefully adjusting the clocks, but something still
> > > seems to be off.
> >
> > Checkout my
> >
> > branch: https://github.com/aford173/linux/commit/183cf6d154afeb9b0300500b09d7b8ec53047a12

Thanks for the pointer.

> >
> > I found that certain resolutions don't properly round, and it seemed
> > to be related to the size of HFP.  HFP of 110 when divded between 4
> > lanes, required a round-up, but then I had to recalculate the rest of
> > the horizontal timings to compensate.
> >
> > I was going to push that as an RFC, but I will investigate your patch
> > series first.  With my small rounding correction, I am able to get
> > 720x480 and 720p on my imx8mp, but not my mini/nano, so I am hoping
> > your patch series fixes that issue for me.
> >
> > >
> > > Unfortunately, a few more modes are still not working at all. The NXP
> > > downstream kernel has some quirks to handle some of the modes especially
> > > wrt. to the porches, but I cannot figure out, what the driver should
> > > actually do in these cases. Maybe there is still an error in the
> > > calculation of the porches and someone at NXP can chime in.
> >
> > Hopefully the comment in my above patch explains how the calculation
> > is corrected and adjusted to get some of the missing resolutions.
> 
> I tested my above patch and it works to sync 720p-60 on my imx8mp, but
> it doesn't seem to sync on my imx8mm using the same monitor and HDMI
> cable.  I don't have a DSI analyzer, so I might still send out a
> modified version of my patch as an RFC once this gets approved.

I tested your patch with all modes of my monitor. 720p-60 doesn't work on my
imx8mn either. The results are the same for DIV_ROUND_CLOSEST and
DIV64_U64_ROUND_UP, but I didn't check for differences in the actually
calculated HFP, yet.

Michael

> 
> adam
> >
> > > Michael
> > >
> > > Signed-off-by: Michael Tretter <m.tretter@...gutronix.de>
> >
> > I'll try to reivew this week and respond with my feedback.
> >
> > adam
> >
> > > ---
> > > Marco Felsch (1):
> > >       drm/bridge: samsung-dsim: add more mipi-dsi device debug information
> > >
> > > Michael Tretter (4):
> > >       drm/bridge: samsung-dsim: reread ref clock before configuring PLL
> > >       drm/bridge: samsung-dsim: update PLL reference clock
> > >       drm/bridge: samsung-dsim: adjust porches by rounding up
> > >       drm/bridge: samsung-dsim: calculate porches in Hz
> > >
> > >  drivers/gpu/drm/bridge/samsung-dsim.c | 42 +++++++++++++++++++++++++----------
> > >  include/drm/bridge/samsung-dsim.h     |  1 +
> > >  2 files changed, 31 insertions(+), 12 deletions(-)
> > > ---
> > > base-commit: 2dde18cd1d8fac735875f2e4987f11817cc0bc2c
> > > change-id: 20230818-samsung-dsim-42346444bce5
> > >
> > > Best regards,
> > > --
> > > Michael Tretter <m.tretter@...gutronix.de>
> > >
> 

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