linux-kernel - Re: [PATCH 3/6] drm: bridge: samsung-dsim: Fetch pll-clock-frequency automatically

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Date:   Fri, 21 Apr 2023 06:44:55 -0500
From:   Adam Ford <aford173@...il.com>
To:     Marek Szyprowski <m.szyprowski@...sung.com>
Cc:     dri-devel@...ts.freedesktop.org, marex@...x.de,
        aford@...conembedded.com, Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Shawn Guo <shawnguo@...nel.org>,
        Sascha Hauer <s.hauer@...gutronix.de>,
        Pengutronix Kernel Team <kernel@...gutronix.de>,
        Fabio Estevam <festevam@...il.com>,
        NXP Linux Team <linux-imx@....com>,
        Inki Dae <inki.dae@...sung.com>,
        Jagan Teki <jagan@...rulasolutions.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>, devicetree@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/6] drm: bridge: samsung-dsim: Fetch pll-clock-frequency automatically

On Fri, Apr 21, 2023 at 6:25 AM Marek Szyprowski
<m.szyprowski@...sung.com> wrote:
>
> On 15.04.2023 12:41, Adam Ford wrote:
> > Fetch the clock rate of "sclk_mipi" (or "pll_clk") instead of
> > having an entry in the device tree for samsung,pll-clock-frequency.
> >
> > Signed-off-by: Adam Ford <aford173@...il.com>
>
> This one breaks DSI panel operation on my Exynos-based Trats, Trats2 and
> TM2e boards. I've didn't check the details, but probably something is
> missing in the dts to make it working properly. Surprisingly the display
> is still working fine on Arndale board with DSI TC358764 bridge.

Thanks for testing!  I'm going to update this patch in V2 which will
use the device tree settings if they are present.  If they are
missing, they will fetch the clock rate instead of failing.  This way,
it should mitigate breaking your boards, but it will allow the imx8m
mini/nano/plus to eliminate hard-coding some device tree entries since
they can be fetched automatically.

adam
>
> > ---
> >   drivers/gpu/drm/bridge/samsung-dsim.c | 12 ++++++------
> >   1 file changed, 6 insertions(+), 6 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/bridge/samsung-dsim.c b/drivers/gpu/drm/bridge/samsung-dsim.c
> > index 9fec32b44e05..73f0c3fbbdf5 100644
> > --- a/drivers/gpu/drm/bridge/samsung-dsim.c
> > +++ b/drivers/gpu/drm/bridge/samsung-dsim.c
> > @@ -1744,11 +1744,6 @@ static int samsung_dsim_parse_dt(struct samsung_dsim *dsi)
> >       struct device_node *node = dev->of_node;
> >       int ret;
> >
> > -     ret = samsung_dsim_of_read_u32(node, "samsung,pll-clock-frequency",
> > -                                    &dsi->pll_clk_rate);
> > -     if (ret < 0)
> > -             return ret;
> > -
> >       ret = samsung_dsim_of_read_u32(node, "samsung,burst-clock-frequency",
> >                                      &dsi->burst_clk_rate);
> >       if (ret < 0)
> > @@ -1823,13 +1818,18 @@ int samsung_dsim_probe(struct platform_device *pdev)
> >               if (IS_ERR(dsi->clks[i])) {
> >                       if (strcmp(clk_names[i], "sclk_mipi") == 0) {
> >                               dsi->clks[i] = devm_clk_get(dev, OLD_SCLK_MIPI_CLK_NAME);
> > -                             if (!IS_ERR(dsi->clks[i]))
> > +                             if (!IS_ERR(dsi->clks[i])) {
> > +                                     dsi->pll_clk_rate = clk_get_rate(dsi->clks[i]);
> >                                       continue;
> > +                             }
> >                       }
> >
> >                       dev_info(dev, "failed to get the clock: %s\n", clk_names[i]);
> >                       return PTR_ERR(dsi->clks[i]);
> >               }
> > +
> > +             if (strcmp(clk_names[i], "sclk_mipi") == 0)
> > +                     dsi->pll_clk_rate = clk_get_rate(dsi->clks[i]);
> >       }
> >
> >       dsi->reg_base = devm_platform_ioremap_resource(pdev, 0);
>
> Best regards
> --
> Marek Szyprowski, PhD
> Samsung R&D Institute Poland
>