linux-kernel - Re: [PATCH 4/6] drm: bridge: samsung-dsim: Dynamically configure DPHY timing

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Message-ID: <CAHCN7xKmFzuwFVO1eR8fdVQ9iXUuB0zVadFYG5_6t8p0=dPG+w@mail.gmail.com>
Date:   Mon, 17 Apr 2023 21:43:15 -0500
From:   Adam Ford <aford173@...il.com>
To:     Lucas Stach <l.stach@...gutronix.de>
Cc:     dri-devel@...ts.freedesktop.org,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        aford@...conembedded.com,
        Frieder Schrempf <frieder.schrempf@...tron.de>,
        Laurent Pinchart <Laurent.pinchart@...asonboard.com>,
        Andrzej Hajda <andrzej.hajda@...el.com>,
        Fabio Estevam <festevam@...il.com>, m.szyprowski@...sung.com,
        marex@...x.de, Robert Foss <rfoss@...nel.org>,
        David Airlie <airlied@...il.com>,
        Jernej Skrabec <jernej.skrabec@...il.com>,
        Jagan Teki <jagan@...rulasolutions.com>,
        NXP Linux Team <linux-imx@....com>,
        devicetree@...r.kernel.org, Daniel Vetter <daniel@...ll.ch>,
        Jonas Karlman <jonas@...boo.se>,
        Sascha Hauer <s.hauer@...gutronix.de>,
        Inki Dae <inki.dae@...sung.com>,
        Rob Herring <robh+dt@...nel.org>,
        linux-arm-kernel@...ts.infradead.org,
        Neil Armstrong <neil.armstrong@...aro.org>,
        linux-kernel@...r.kernel.org,
        Pengutronix Kernel Team <kernel@...gutronix.de>,
        Shawn Guo <shawnguo@...nel.org>
Subject: Re: [PATCH 4/6] drm: bridge: samsung-dsim: Dynamically configure DPHY timing

On Mon, Apr 17, 2023 at 6:53 AM Adam Ford <aford173@...il.com> wrote:
>
> On Mon, Apr 17, 2023 at 3:38 AM Lucas Stach <l.stach@...gutronix.de> wrote:
> >
> > Hi Adam,
> >
> > Am Samstag, dem 15.04.2023 um 05:41 -0500 schrieb Adam Ford:
> > > NXP uses a lookup table to determine the various values for
> > > the PHY Timing based on the clock rate in their downstream
> > > kernel.  Since the input clock can be variable, the phy
> > > settings need to be variable too.  Add an additional variable
> > > to the driver data to enable this feature to prevent breaking
> > > boards that don't support it.
> > >
> >
> > I haven't checked if this generates values close to the ones in this
> > table, but I guess it should be worth a try to use
> > phy_mipi_dphy_get_default_config() instead.
>
> I didn't know that was a thing.  I like that idea much better than the
> table.  I just pulled what NXP had and tweaked it to fit the mainline.
> I'll give it a try in the next few days, when I have some more time.

I tried phy_mipi_dphy_get_default_config() and the function return
different values than what NXP's table returns, and the screen doesn't
sync properly.  I will try to figure out the mathematical calculation
to generate the values for this DSIM instead of using a lookup table.

adam
>
> adam
> >
> > Regards,
> > Lucas
> >
> > > Signed-off-by: Adam Ford <aford173@...il.com>
> > > ---
> > >  drivers/gpu/drm/bridge/samsung-dsim.c |  85 +++++++--
> > >  drivers/gpu/drm/bridge/samsung-dsim.h | 254 ++++++++++++++++++++++++++
> > >  include/drm/bridge/samsung-dsim.h     |   1 +
> > >  3 files changed, 326 insertions(+), 14 deletions(-)
> > >  create mode 100644 drivers/gpu/drm/bridge/samsung-dsim.h
> > >
> <snip>
> >