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

[Neil Armstrong]

On 24/07/2023 17:16, Frieder Schrempf wrote:

From: Frieder Schrempf <frieder.schre...@kontron.de>

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 <thar...@gateworks.com>
Signed-off-by: Frieder Schrempf <frieder.schre...@kontron.de>
---
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;

Reviewed-by: Neil Armstrong <neil.armstr...@linaro.org>