Re: [PATCH v2 1/2] drm: bridge: samsung-dsim: Fix i.MX8M enable flow to meet spec

[Tim Harvey]

On Wed, May 3, 2023 at 9:33 AM Frieder Schrempf <frieder@xxxxxxx> wrote:
>
> From: Frieder Schrempf <frieder.schrempf@xxxxxxxxxx>
>
> According to the documentation [1] the proper enable flow is:
>
> 1. Enable DSI link and keep data lanes in LP-11 (stop state)
> 2. Disable stop state to bring data lanes into HS mode
>
> Currently we do this all at once within enable(), which doesn't
> allow to meet the requirements of some downstream bridges.
>
> To fix this we now enable the DSI in pre_enable() and force it
> into stop state using the FORCE_STOP_STATE bit in the ESCMODE
> register until enable() is called where we reset the bit.
>
> We currently do this only for i.MX8M as Exynos uses a different
> init flow where samsung_dsim_init() is called from
> samsung_dsim_host_transfer().
>
> [1] https://docs.kernel.org/gpu/drm-kms-helpers.html#mipi-dsi-bridge-operation
>
> Signed-off-by: Frieder Schrempf <frieder.schrempf@xxxxxxxxxx>
> ---
> Changes for v2:
> * Drop RFC
> ---
>  drivers/gpu/drm/bridge/samsung-dsim.c | 25 +++++++++++++++++++++++--
>  1 file changed, 23 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/gpu/drm/bridge/samsung-dsim.c b/drivers/gpu/drm/bridge/samsung-dsim.c
> index e0a402a85787..9775779721d9 100644
> --- a/drivers/gpu/drm/bridge/samsung-dsim.c
> +++ b/drivers/gpu/drm/bridge/samsung-dsim.c
> @@ -859,6 +859,10 @@ static int samsung_dsim_init_link(struct samsung_dsim *dsi)
>         reg = samsung_dsim_read(dsi, DSIM_ESCMODE_REG);
>         reg &= ~DSIM_STOP_STATE_CNT_MASK;
>         reg |= DSIM_STOP_STATE_CNT(driver_data->reg_values[STOP_STATE_CNT]);
> +
> +       if (!samsung_dsim_hw_is_exynos(dsi->plat_data->hw_type))
> +               reg |= DSIM_FORCE_STOP_STATE;
> +
>         samsung_dsim_write(dsi, DSIM_ESCMODE_REG, reg);
>
>         reg = DSIM_BTA_TIMEOUT(0xff) | DSIM_LPDR_TIMEOUT(0xffff);
> @@ -1340,6 +1344,9 @@ static void samsung_dsim_atomic_pre_enable(struct drm_bridge *bridge,
>                 ret = samsung_dsim_init(dsi);
>                 if (ret)
>                         return;
> +
> +               samsung_dsim_set_display_mode(dsi);
> +               samsung_dsim_set_display_enable(dsi, true);
>         }
>  }
>
> @@ -1347,9 +1354,16 @@ static void samsung_dsim_atomic_enable(struct drm_bridge *bridge,
>                                        struct drm_bridge_state *old_bridge_state)
>  {
>         struct samsung_dsim *dsi = bridge_to_dsi(bridge);
> +       u32 reg;
>
> -       samsung_dsim_set_display_mode(dsi);
> -       samsung_dsim_set_display_enable(dsi, true);
> +       if (samsung_dsim_hw_is_exynos(dsi->plat_data->hw_type)) {
> +               samsung_dsim_set_display_mode(dsi);
> +               samsung_dsim_set_display_enable(dsi, true);
> +       } else {
> +               reg = samsung_dsim_read(dsi, DSIM_ESCMODE_REG);
> +               reg &= ~DSIM_FORCE_STOP_STATE;
> +               samsung_dsim_write(dsi, DSIM_ESCMODE_REG, reg);
> +       }
>
>         dsi->state |= DSIM_STATE_VIDOUT_AVAILABLE;
>  }
> @@ -1358,10 +1372,17 @@ static void samsung_dsim_atomic_disable(struct drm_bridge *bridge,
>                                         struct drm_bridge_state *old_bridge_state)
>  {
>         struct samsung_dsim *dsi = bridge_to_dsi(bridge);
> +       u32 reg;
>
>         if (!(dsi->state & DSIM_STATE_ENABLED))
>                 return;
>
> +       if (!samsung_dsim_hw_is_exynos(dsi->plat_data->hw_type)) {
> +               reg = samsung_dsim_read(dsi, DSIM_ESCMODE_REG);
> +               reg |= DSIM_FORCE_STOP_STATE;
> +               samsung_dsim_write(dsi, DSIM_ESCMODE_REG, reg);
> +       }
> +
>         dsi->state &= ~DSIM_STATE_VIDOUT_AVAILABLE;
>  }
>
> --
> 2.40.0
>

Hi Frieder,

I found this patch to break mipi-dsi display on my board which has:
 - FocalTech FT5406 10pt touch controller (with no interrupt)
 - Powertip PH800480T013-IDF02 compatible panel
 - Toshiba TC358762 compatible DSI to DBI bridge
 - ATTINY based regulator used for backlight controller and panel enable

I enable this via a dt overlay in a pending patch
imx8mm-venice-gw72xx-0x-rpidsi.dtso [1] which works on 6.4 but not
6.5-rc1 which has this patch.

The issue appears as:
[    6.110585] samsung-dsim 32e60000.dsi: xfer timed out: 29 06 00 00
64 01 05 00 00 00
[    6.326588] tc358762 32e60000.dsi.0: error initializing bridge (-110)

Instead of
[    1.011729] samsung-dsim 32e10000.dsi: supply vddcore not found,
using dummy regulator
[    1.019829] samsung-dsim 32e10000.dsi: supply vddio not found,
using dummy regulator
[    5.649928] samsung-dsim 32e10000.dsi:
[drm:samsung_dsim_host_attach] Attached tc358762 device

I'm curious what board/panel were you needing this for and do you have
any ideas why it broke my setup?

I'm also curious what board/panel Alexander tested this with and if
Adam or Jagan (or others) have tested this with their hardware?

best regards,

Tim
[1] https://patchwork.kernel.org/project/linux-arm-kernel/patch/20230711221124.2127186-1-tharvey@xxxxxxxxxxxxx/