linux-kernel - Re: [PATCH v2 2/2] drm/bridge: ti-sn65dsi83: Fix enable/disable flow to meet spec

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Message-ID: <e819f7c7-5023-ce9b-3787-1fb152745f0e@linaro.org>
Date:   Tue, 16 May 2023 09:33:33 +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, linux-kernel@...r.kernel.org,
        Robert Foss <rfoss@...nel.org>
Cc:     Frieder Schrempf <frieder.schrempf@...tron.de>,
        Alexander Stein <alexander.stein@...tq-group.com>,
        Jernej Skrabec <jernej.skrabec@...il.com>,
        Jonas Karlman <jonas@...boo.se>,
        Laurent Pinchart <Laurent.pinchart@...asonboard.com>,
        Marek Vasut <marex@...x.de>, Sam Ravnborg <sam@...nborg.org>,
        Uwe Kleine-König <u.kleine-koenig@...gutronix.de>,
        Ville Syrjälä <ville.syrjala@...ux.intel.com>
Subject: Re: [PATCH v2 2/2] drm/bridge: ti-sn65dsi83: Fix enable/disable flow
 to meet spec

On 03/05/2023 18:33, Frieder Schrempf wrote:
> From: Frieder Schrempf <frieder.schrempf@...tron.de>
> 
> The datasheet describes the following initialization flow including
> minimum delay times between each step:
> 
> 1. DSI data lanes need to be in LP-11 and the clock lane in HS mode
> 2. toggle EN signal
> 3. initialize registers
> 4. enable PLL
> 5. soft reset
> 6. enable DSI stream
> 7. check error status register
> 
> To meet this requirement we need to make sure the host bridge's
> pre_enable() is called first by using the pre_enable_prev_first
> flag.
> 
> Furthermore we need to split enable() into pre_enable() which covers
> steps 2-5 from above and enable() which covers step 7 and is called
> after the host bridge's enable().
> 
> Signed-off-by: Frieder Schrempf <frieder.schrempf@...tron.de>
> ---
> Changes for v2:
> * Drop RFC
> ---
>   drivers/gpu/drm/bridge/ti-sn65dsi83.c | 19 ++++++++++++++++---
>   1 file changed, 16 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/gpu/drm/bridge/ti-sn65dsi83.c b/drivers/gpu/drm/bridge/ti-sn65dsi83.c
> index 75286c9afbb9..a82f10b8109f 100644
> --- a/drivers/gpu/drm/bridge/ti-sn65dsi83.c
> +++ b/drivers/gpu/drm/bridge/ti-sn65dsi83.c
> @@ -321,8 +321,8 @@ static u8 sn65dsi83_get_dsi_div(struct sn65dsi83 *ctx)
>   	return dsi_div - 1;
>   }
>   
> -static void sn65dsi83_atomic_enable(struct drm_bridge *bridge,
> -				    struct drm_bridge_state *old_bridge_state)
> +static void sn65dsi83_atomic_pre_enable(struct drm_bridge *bridge,
> +					struct drm_bridge_state *old_bridge_state)
>   {
>   	struct sn65dsi83 *ctx = bridge_to_sn65dsi83(bridge);
>   	struct drm_atomic_state *state = old_bridge_state->base.state;
> @@ -484,11 +484,22 @@ static void sn65dsi83_atomic_enable(struct drm_bridge *bridge,
>   	/* Trigger reset after CSR register update. */
>   	regmap_write(ctx->regmap, REG_RC_RESET, REG_RC_RESET_SOFT_RESET);
>   
> +	/* Wait for 10ms after soft reset as specified in datasheet */
> +	usleep_range(10000, 12000);
> +}
> +
> +static void sn65dsi83_atomic_enable(struct drm_bridge *bridge,
> +				    struct drm_bridge_state *old_bridge_state)
> +{
> +	struct sn65dsi83 *ctx = bridge_to_sn65dsi83(bridge);
> +	unsigned int pval;
> +
>   	/* Clear all errors that got asserted during initialization. */
>   	regmap_read(ctx->regmap, REG_IRQ_STAT, &pval);
>   	regmap_write(ctx->regmap, REG_IRQ_STAT, pval);
>   
> -	usleep_range(10000, 12000);
> +	/* Wait for 1ms and check for errors in status register */
> +	usleep_range(1000, 1100);
>   	regmap_read(ctx->regmap, REG_IRQ_STAT, &pval);
>   	if (pval)
>   		dev_err(ctx->dev, "Unexpected link status 0x%02x\n", pval);
> @@ -555,6 +566,7 @@ static const struct drm_bridge_funcs sn65dsi83_funcs = {
>   	.attach			= sn65dsi83_attach,
>   	.detach			= sn65dsi83_detach,
>   	.atomic_enable		= sn65dsi83_atomic_enable,
> +	.atomic_pre_enable	= sn65dsi83_atomic_pre_enable,
>   	.atomic_disable		= sn65dsi83_atomic_disable,
>   	.mode_valid		= sn65dsi83_mode_valid,
>   
> @@ -697,6 +709,7 @@ static int sn65dsi83_probe(struct i2c_client *client)
>   
>   	ctx->bridge.funcs = &sn65dsi83_funcs;
>   	ctx->bridge.of_node = dev->of_node;
> +	ctx->bridge.pre_enable_prev_first = true;
>   	drm_bridge_add(&ctx->bridge);
>   
>   	ret = sn65dsi83_host_attach(ctx);

Reviewed-by: Neil Armstrong <neil.armstrong@...aro.org>