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

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Message-ID: <0f81553d-1d68-43e5-aa49-4801ba7c7d51@linaro.org>
Date:   Fri, 18 Aug 2023 10:37:24 +0200
From:   Neil Armstrong <neil.armstrong@...aro.org>
To:     Frieder Schrempf <frieder@...s.de>,
        Andrzej Hajda <andrzej.hajda@...el.com>,
        Daniel Vetter <daniel@...ll.ch>,
        David Airlie <airlied@...il.com>,
        dri-devel@...ts.freedesktop.org,
        Frieder Schrempf <frieder.schrempf@...tron.de>,
        Inki Dae <inki.dae@...sung.com>,
        Jagan Teki <jagan@...rulasolutions.com>,
        linux-kernel@...r.kernel.org,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        Robert Foss <rfoss@...nel.org>
Cc:     Tim Harvey <tharvey@...eworks.com>, Adam Ford <aford173@...il.com>,
        Jernej Skrabec <jernej.skrabec@...il.com>,
        Jonas Karlman <jonas@...boo.se>,
        Laurent Pinchart <Laurent.pinchart@...asonboard.com>,
        Marek Vasut <marex@...x.de>
Subject: Re: [PATCH v2] drm: bridge: samsung-dsim: Fix init during host
 transfer

On 24/07/2023 17:16, Frieder Schrempf wrote:
> From: Frieder Schrempf <frieder.schrempf@...tron.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 <tharvey@...eworks.com>
> Signed-off-by: Frieder Schrempf <frieder.schrempf@...tron.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.armstrong@...aro.org>