Re: [PATCH 2/5] drm/bridge: samsung-dsim: reread ref clock before configuring PLL

[Inki Dae]

2023년 8월 29일 (화) 오전 12:59, Michael Tretter <m.tretter@xxxxxxxxxxxxxx>님이 작성:

>
> The PLL reference clock may change at runtime. Thus, reading the clock
> rate during probe is not sufficient to correctly configure the PLL for
> the expected hs clock.
>
> Read the actual rate of the reference clock before calculating the PLL
> configuration parameters.
>
> Signed-off-by: Michael Tretter <m.tretter@xxxxxxxxxxxxxx>
> ---
>  drivers/gpu/drm/bridge/samsung-dsim.c | 16 +++++++++-------
>  include/drm/bridge/samsung-dsim.h     |  1 +
>  2 files changed, 10 insertions(+), 7 deletions(-)
>
> diff --git a/drivers/gpu/drm/bridge/samsung-dsim.c b/drivers/gpu/drm/bridge/samsung-dsim.c
> index 6778f1751faa..da90c2038042 100644
> --- a/drivers/gpu/drm/bridge/samsung-dsim.c
> +++ b/drivers/gpu/drm/bridge/samsung-dsim.c
> @@ -611,7 +611,12 @@ static unsigned long samsung_dsim_set_pll(struct samsung_dsim *dsi,
>         u16 m;
>         u32 reg;
>
> -       fin = dsi->pll_clk_rate;
> +       if (dsi->pll_clk)
> +               fin = clk_get_rate(dsi->pll_clk);
> +       else
> +               fin = dsi->pll_clk_rate;
> +       dev_dbg(dsi->dev, "PLL ref clock freq %lu\n", fin);
> +

Could you share us the actual use case that in runtime the pll
reference clock can be changed?

This patch is trying to change clock binding behavior which is
described in dt binding[1]
[1] Documentation/devicetree/bindings/display/bridge/samsung,mipi-dsim.yaml

It says,
"DISM oscillator clock frequency. If absent, the clock frequency of
sclk_mipi will be used instead."

However, this patch makes the sclk_mipi to be used first.

Thanks,
Inki Dae

>         fout = samsung_dsim_pll_find_pms(dsi, fin, freq, &p, &m, &s);
>         if (!fout) {
>                 dev_err(dsi->dev,
> @@ -1821,18 +1826,15 @@ static int samsung_dsim_parse_dt(struct samsung_dsim *dsi)
>         u32 lane_polarities[5] = { 0 };
>         struct device_node *endpoint;
>         int i, nr_lanes, ret;
> -       struct clk *pll_clk;
>
>         ret = samsung_dsim_of_read_u32(node, "samsung,pll-clock-frequency",
>                                        &dsi->pll_clk_rate, 1);
>         /* If it doesn't exist, read it from the clock instead of failing */
>         if (ret < 0) {
>                 dev_dbg(dev, "Using sclk_mipi for pll clock frequency\n");
> -               pll_clk = devm_clk_get(dev, "sclk_mipi");
> -               if (!IS_ERR(pll_clk))
> -                       dsi->pll_clk_rate = clk_get_rate(pll_clk);
> -               else
> -                       return PTR_ERR(pll_clk);
> +               dsi->pll_clk = devm_clk_get(dev, "sclk_mipi");
> +               if (IS_ERR(dsi->pll_clk))
> +                       return PTR_ERR(dsi->pll_clk);
>         }
>
>         /* If it doesn't exist, use pixel clock instead of failing */
> diff --git a/include/drm/bridge/samsung-dsim.h b/include/drm/bridge/samsung-dsim.h
> index 05100e91ecb9..31ff88f152fb 100644
> --- a/include/drm/bridge/samsung-dsim.h
> +++ b/include/drm/bridge/samsung-dsim.h
> @@ -87,6 +87,7 @@ struct samsung_dsim {
>         void __iomem *reg_base;
>         struct phy *phy;
>         struct clk **clks;
> +       struct clk *pll_clk;
>         struct regulator_bulk_data supplies[2];
>         int irq;
>         struct gpio_desc *te_gpio;
>
> --
> 2.39.2
>