linux-kernel - Re: [PATCH V2 4/6] drm: bridge: samsung-dsim: Dynamically configure DPHY timing

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Message-ID: <ceee0290-211b-a675-2ba5-9342ee27fc49@samsung.com>
Date:   Mon, 24 Apr 2023 11:47:09 +0200
From:   Marek Szyprowski <m.szyprowski@...sung.com>
To:     Chen-Yu Tsai <wenst@...omium.org>, Adam Ford <aford173@...il.com>
Cc:     dri-devel@...ts.freedesktop.org, Marek Vasut <marex@...x.de>,
        Neil Armstrong <neil.armstrong@...aro.org>,
        Robert Foss <rfoss@...nel.org>,
        Jonas Karlman <jonas@...boo.se>,
        Laurent Pinchart <Laurent.pinchart@...asonboard.com>,
        aford@...conembedded.com,
        Jernej Skrabec <jernej.skrabec@...il.com>,
        linux-kernel@...r.kernel.org,
        Jagan Teki <jagan@...rulasolutions.com>,
        Andrzej Hajda <andrzej.hajda@...el.com>,
        dario.binacchi@...rulasolutions.com
Subject: Re: [PATCH V2 4/6] drm: bridge: samsung-dsim: Dynamically configure
 DPHY timing

On 24.04.2023 11:44, Chen-Yu Tsai wrote:
> On Mon, Apr 24, 2023 at 5:31 PM Adam Ford <aford173@...il.com> wrote:
>> On Mon, Apr 24, 2023 at 1:12 AM Chen-Yu Tsai <wenst@...omium.org> wrote:
>>> On Sun, Apr 23, 2023 at 8:13 PM Adam Ford <aford173@...il.com> wrote:
>>>> 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.
>>>>
>>>> Signed-off-by: Adam Ford <aford173@...il.com>
>>>> ---
>>>>   drivers/gpu/drm/bridge/samsung-dsim.c | 79 +++++++++++++++++++++++----
>>>>   include/drm/bridge/samsung-dsim.h     |  1 +
>>>>   2 files changed, 70 insertions(+), 10 deletions(-)
>>>>
>>>> diff --git a/drivers/gpu/drm/bridge/samsung-dsim.c b/drivers/gpu/drm/bridge/samsung-dsim.c
>>>> index 5b6e7825b92f..f165483d5044 100644
>>>> --- a/drivers/gpu/drm/bridge/samsung-dsim.c
>>>> +++ b/drivers/gpu/drm/bridge/samsung-dsim.c
>>>> @@ -18,9 +18,7 @@
>>>>   #include <linux/media-bus-format.h>
>>>>   #include <linux/of_device.h>
>>>>   #include <linux/phy/phy.h>
>>>> -
>>>>   #include <video/mipi_display.h>
>>>> -
>>>>   #include <drm/bridge/samsung-dsim.h>
>>>>   #include <drm/drm_panel.h>
>>>>   #include <drm/drm_print.h>
>>>> @@ -218,6 +216,8 @@
>>>>
>>>>   #define OLD_SCLK_MIPI_CLK_NAME         "pll_clk"
>>>>
>>>> +#define PS_TO_CYCLE(PS, MHz) DIV64_U64_ROUND_CLOSEST(((PS) * (MHz)), 1000000000000ULL)
>>>> +
>>>>   static const char *const clk_names[5] = {
>>>>          "bus_clk",
>>>>          "sclk_mipi",
>>>> @@ -487,6 +487,7 @@ static const struct samsung_dsim_driver_data imx8mm_dsi_driver_data = {
>>>>          .m_min = 64,
>>>>          .m_max = 1023,
>>>>          .vco_min = 1050,
>>>> +       .dynamic_dphy = 1,
>>>>   };
>>>>
>>>>   static const struct samsung_dsim_driver_data *
>>>> @@ -698,13 +699,50 @@ static void samsung_dsim_set_phy_ctrl(struct samsung_dsim *dsi)
>>>>          const struct samsung_dsim_driver_data *driver_data = dsi->driver_data;
>>>>          const unsigned int *reg_values = driver_data->reg_values;
>>>>          u32 reg;
>>>> +       struct drm_display_mode *m = &dsi->mode;
>>>> +       int bpp = mipi_dsi_pixel_format_to_bpp(dsi->format);
>>>> +       struct phy_configure_opts_mipi_dphy cfg;
>>>> +       int clk_prepare, lpx, clk_zero, clk_post, clk_trail;
>>>> +       int hs_exit, hs_prepare, hs_zero, hs_trail;
>>>> +       unsigned long long clock_in_hz = m->clock * 1000;
>>>>
>>>>          if (driver_data->has_freqband)
>>>>                  return;
>>>>
>>>> +       /* The dynamic_phy has the ability to adjust PHY Timing settings */
>>>> +       if (driver_data->dynamic_dphy) {
>>>> +               phy_mipi_dphy_get_default_config(clock_in_hz, bpp, dsi->lanes, &cfg);
>>> This requires adding "select GENERIC_PHY_MIPI_DPHY" to DRM_SAMSUNG_DSIM,
>>> otherwise with CONFIG_DRM_SAMSUNG_DSIM=m:
>>>
>>> ERROR: modpost: "phy_mipi_dphy_get_default_config"
>>> [drivers/gpu/drm/bridge/samsung-dsim.ko] undefined!
>>> make[5]: *** [scripts/Makefile.modpost:136: Module.symvers] Error 1
>>> make[4]: *** [Makefile:1978: modpost] Error 2
>>> make[3]: *** [Makefile:357: __build_one_by_one] Error 2
>>>
>>> I'm sure there'll be a similar error if CONFIG_DRM_SAMSUNG_DSIM=y.
>> That's interesting, I didn't come across that.
>> What did you use for a starting point when you applied the patches?
>> I want to see if I can replicate it.
> next-20230421. My config is pretty much tailored to the Hummingbird Pulse.
> Device drivers for other hardware or things that I can't enable are all
> disabled. For example I don't have PHY_MIXEL_MIPI_DPHY enabled.
>
> Maybe you have some other bridge or phy that selects it enabled?


I've observed similar issue while building exynos_defconfig for arm 32bit.


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