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

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Message-ID: <96150852-84ce-f750-2e2e-8cb53cde5719@samsung.com>
Date:   Mon, 15 May 2023 09:37:06 +0200
From:   Marek Szyprowski <m.szyprowski@...sung.com>
To:     Adam Ford <aford173@...il.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 13.05.2023 06:25, Adam Ford wrote:
> 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://protect2.fireeye.com/v1/url?k=2eeb1ed9-4e098384-2eea9596-000babd9f1ba-9ad5c339e5ea6e4d&q=1&e=652be603-d622-4d0e-95d3-639656ab1af1&u=https%3A%2F%2Fgithub.com%2Faford173%2Flinux%2Ftree%2Fdsim-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.

The above mentioned 'dsim-updates-wip' branch works fine on all my 
Exynos based boards.


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