linux-kernel - Re: [PATCH V5 5/6] drm: bridge: samsung-dsim: Dynamically configure DPHY timing

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Message-ID: <CAHCN7xLZNvMx=U9=Fp=qrG9xaMhU1PS_nQO5FfC2S+XLO8YLXQ@mail.gmail.com>
Date:   Fri, 12 May 2023 23:25:58 -0500
From:   Adam Ford <aford173@...il.com>
To:     Marek Szyprowski <m.szyprowski@...sung.com>
Cc:     Lucas Stach <l.stach@...gutronix.de>,
        dri-devel@...ts.freedesktop.org, Marek Vasut <marex@...x.de>,
        Neil Armstrong <neil.armstrong@...aro.org>,
        Jernej Skrabec <jernej.skrabec@...il.com>,
        Robert Foss <rfoss@...nel.org>,
        Jonas Karlman <jonas@...boo.se>, aford@...conembedded.com,
        Frieder Schrempf <frieder.schrempf@...tron.de>,
        linux-kernel@...r.kernel.org, Michael Walle <michael@...le.cc>,
        Laurent Pinchart <Laurent.pinchart@...asonboard.com>,
        Andrzej Hajda <andrzej.hajda@...el.com>,
        Chen-Yu Tsai <wenst@...omium.org>,
        Jagan Teki <jagan@...rulasolutions.com>
Subject: Re: [PATCH V5 5/6] drm: bridge: samsung-dsim: Dynamically configure
 DPHY timing

On Fri, May 12, 2023 at 4:02 PM Marek Szyprowski
<m.szyprowski@...sung.com> wrote:
>
> On 12.05.2023 22:00, Adam Ford wrote:
> > On Fri, May 12, 2023 at 2:37 PM Lucas Stach <l.stach@...gutronix.de> wrote:
> >> Am Samstag, dem 06.05.2023 um 14:24 -0500 schrieb Adam Ford:
> >>> The DPHY timings are currently hard coded. Since the input
> >>> clock can be variable, the phy timings 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.
> >>>
> >>> The phy_mipi_dphy_get_default_config function configures the
> >>> DPHY timings in pico-seconds, and a small macro converts those
> >>> timings into clock cycles based on the pixel clock rate.
> >>>
> >> This week I finally had some time to take a deeper look at this series
> >> and test it on some of my systems.
> > Thanks for testing this!
> >> This patch causes issues when the burst clock rate is fixed by
> >> supplying the DT entry. Instead of describing the issue below, I'm
> >> attaching the patch that makes things work on my system.
> > Oops, sorry about that.
> >
> >> I would appreciate if you could test this one on your side. Feel free
> >> to squash it into yours if you find it working properly.
> > I reviewed your patch, and it looks like it makes a lot of sense.
> > If it works, I'll squash them together and add your name to the sign-off.

That worked really well, I'll add it to my WIP directory since Marek S
said he'd test the other proposal of dropping the dynamic phy flag and
corresponding check in favor of pushing everyone to the same code.

> >
> >> Also I would almost bet that dynamic_dphy is working on the Exynos
> >> boards with that fix added. So if anyone with access to those boards
> >> would like to give it a shot, we may be able to get rid of the
> >> hardcoded PHY parameters altogether, which would be a nice cleanup.
> > I wondered the same thing, but I didn't want to create more work for
> > Marek S and since there was so much churn getting the original driver
> > ported, I thought it would be the safest thing to try to give the
> > imx8m m/n/p the features without breaking the Exynos.
> >
> > Marek S - Do you want me to post this file without the extra checks to
> > see if it still works with Exynos?
>
> Feel free to send me patches to test or just point to your
> work-in-progress git repo.

Thanks for testing this, Marek S.  My work-in-progress branch is:

https://github.com/aford173/linux/tree/dsim-updates-wip

Depending on what you find will determine how I modify the next
revision of the code I push, so I very much appreciate your feedback.
Hopefully the suggestion from Lucas will work for your applications
and we can reduce some of the code complexity.

adam
>
>
> Best regards
> --
> Marek Szyprowski, PhD
> Samsung R&D Institute Poland
>