Re: [PATCH v2] drm: bridge: samsung-dsim: Fix init during host transfer

[Tim Harvey]

On Mon, Jul 24, 2023 at 8:16 AM Frieder Schrempf <frieder@xxxxxxx> wrote:
>
> From: Frieder Schrempf <frieder.schrempf@xxxxxxxxxx>
>
> In case the downstream bridge or panel uses DSI transfers before the
> DSI host was actually initialized through samsung_dsim_atomic_enable()
> which clears the stop state (LP11) mode, all transfers will fail.
>
> This happens with downstream bridges that are controlled by DSI
> commands such as the tc358762.
>
> As documented in [1] DSI hosts are expected to allow transfers
> outside the normal bridge enable/disable flow.
>
> To fix this make sure that stop state is cleared in
> samsung_dsim_host_transfer() which restores the previous
> behavior.
>
> We also factor out the common code to enable/disable stop state
> to samsung_dsim_set_stop_state().
>
> [1] https://docs.kernel.org/gpu/drm-kms-helpers.html#mipi-dsi-bridge-operation
>
> Fixes: 0c14d3130654 ("drm: bridge: samsung-dsim: Fix i.MX8M enable flow to meet spec")
> Reported-by: Tim Harvey <tharvey@xxxxxxxxxxxxx>
> Signed-off-by: Frieder Schrempf <frieder.schrempf@xxxxxxxxxx>
> ---
> Changes for v2:
>   * Fix reversed stop state enable/disable in samsung_dsim_set_stop_state()
>
> Hi Tim, could you please give this patch a try and report back if
> it fixes your problem? Thanks!
> ---
>  drivers/gpu/drm/bridge/samsung-dsim.c | 27 +++++++++++++++++----------
>  1 file changed, 17 insertions(+), 10 deletions(-)
>
> diff --git a/drivers/gpu/drm/bridge/samsung-dsim.c b/drivers/gpu/drm/bridge/samsung-dsim.c
> index 043b8109e64a..73ec60757dbc 100644
> --- a/drivers/gpu/drm/bridge/samsung-dsim.c
> +++ b/drivers/gpu/drm/bridge/samsung-dsim.c
> @@ -1386,6 +1386,18 @@ static void samsung_dsim_disable_irq(struct samsung_dsim *dsi)
>         disable_irq(dsi->irq);
>  }
>
> +static void samsung_dsim_set_stop_state(struct samsung_dsim *dsi, bool enable)
> +{
> +       u32 reg = samsung_dsim_read(dsi, DSIM_ESCMODE_REG);
> +
> +       if (enable)
> +               reg |= DSIM_FORCE_STOP_STATE;
> +       else
> +               reg &= ~DSIM_FORCE_STOP_STATE;
> +
> +       samsung_dsim_write(dsi, DSIM_ESCMODE_REG, reg);
> +}
> +
>  static int samsung_dsim_init(struct samsung_dsim *dsi)
>  {
>         const struct samsung_dsim_driver_data *driver_data = dsi->driver_data;
> @@ -1445,15 +1457,12 @@ 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;
>
>         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);
> +               samsung_dsim_set_stop_state(dsi, false);
>         }
>
>         dsi->state |= DSIM_STATE_VIDOUT_AVAILABLE;
> @@ -1463,16 +1472,12 @@ 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);
> -       }
> +       if (!samsung_dsim_hw_is_exynos(dsi->plat_data->hw_type))
> +               samsung_dsim_set_stop_state(dsi, true);
>
>         dsi->state &= ~DSIM_STATE_VIDOUT_AVAILABLE;
>  }
> @@ -1775,6 +1780,8 @@ static ssize_t samsung_dsim_host_transfer(struct mipi_dsi_host *host,
>         if (ret)
>                 return ret;
>
> +       samsung_dsim_set_stop_state(dsi, false);
> +
>         ret = mipi_dsi_create_packet(&xfer.packet, msg);
>         if (ret < 0)
>                 return ret;
> --
> 2.41.0
>

Frieder,

Sorry for the delay. Yes this resolves the regression I ran into. I
tested it on top of v6.5-rc6 on a gw72xx-0x with a DFROBOT DRF0678 7in
800x480 (Raspberry Pi) display which has the Toshiba TC358762
compatible DSI to DBI bridge.

Let's please get this into v6.5 as soon as possible.

Best regards,

Tim