linux-kernel - Re: [PATCH v3 1/3] drm/bridge: ti-sn65dsi86: Support DisplayPort (non-eDP) mode

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Date:   Thu, 10 Mar 2022 18:18:25 +0200
From:   Laurent Pinchart <laurent.pinchart@...asonboard.com>
To:     Kieran Bingham <kieran.bingham+renesas@...asonboard.com>
Cc:     dri-devel@...ts.freedesktop.org, linux-renesas-soc@...r.kernel.org,
        Sam Ravnborg <sam@...nborg.org>,
        Douglas Anderson <dianders@...omium.org>,
        linux-kernel@...r.kernel.org,
        Andrzej Hajda <andrzej.hajda@...el.com>,
        Neil Armstrong <narmstrong@...libre.com>,
        Robert Foss <robert.foss@...aro.org>,
        Jonas Karlman <jonas@...boo.se>,
        Jernej Skrabec <jernej.skrabec@...il.com>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>
Subject: Re: [PATCH v3 1/3] drm/bridge: ti-sn65dsi86: Support DisplayPort
 (non-eDP) mode

Hi Kieran,

Thank you for the patch.

On Thu, Mar 10, 2022 at 03:22:25PM +0000, Kieran Bingham wrote:
> From: Laurent Pinchart <laurent.pinchart+renesas@...asonboard.com>
> 
> Despite the SN65DSI86 being an eDP bridge, on some systems its output is
> routed to a DisplayPort connector. Enable DisplayPort mode when the next
> component in the display pipeline is detected as a DisplayPort
> connector, and disable eDP features in that case.
> 
> Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@...asonboard.com>
> Reworked to set bridge type based on the next bridge/connector.
> Signed-off-by: Kieran Bingham <kieran.bingham+renesas@...asonboard.com>

Reviewed-by: Laurent Pinchart <laurent.pinchart@...asonboard.com>

(I know I'm listed as the author, but your changes look good :-))

> --
> Changes since v1/RFC:
>  - Rebased on top of "drm/bridge: ti-sn65dsi86: switch to
>    devm_drm_of_get_bridge"
>  - eDP/DP mode determined from the next bridge connector type.
> 
> Changes since v2:
>  - Remove setting of Standard DP Scrambler Seed. (It's read-only).
>  - Prevent setting DP_EDP_CONFIGURATION_SET in
>    ti_sn_bridge_atomic_enable()
>  - Use Doug's suggested text for disabling ASSR on DP mode.
> 
>  drivers/gpu/drm/bridge/ti-sn65dsi86.c | 23 ++++++++++++++++++++---
>  1 file changed, 20 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/gpu/drm/bridge/ti-sn65dsi86.c b/drivers/gpu/drm/bridge/ti-sn65dsi86.c
> index c892ecba91c7..93b54fcba8ba 100644
> --- a/drivers/gpu/drm/bridge/ti-sn65dsi86.c
> +++ b/drivers/gpu/drm/bridge/ti-sn65dsi86.c
> @@ -62,6 +62,7 @@
>  #define SN_LN_ASSIGN_REG			0x59
>  #define  LN_ASSIGN_WIDTH			2
>  #define SN_ENH_FRAME_REG			0x5A
> +#define  ASSR_CONTROL				BIT(0)
>  #define  VSTREAM_ENABLE				BIT(3)
>  #define  LN_POLRS_OFFSET			4
>  #define  LN_POLRS_MASK				0xf0
> @@ -93,6 +94,8 @@
>  #define SN_DATARATE_CONFIG_REG			0x94
>  #define  DP_DATARATE_MASK			GENMASK(7, 5)
>  #define  DP_DATARATE(x)				((x) << 5)
> +#define SN_TRAINING_SETTING_REG			0x95
> +#define  SCRAMBLE_DISABLE			BIT(4)
>  #define SN_ML_TX_MODE_REG			0x96
>  #define  ML_TX_MAIN_LINK_OFF			0
>  #define  ML_TX_NORMAL_MODE			BIT(0)
> @@ -982,6 +985,17 @@ static int ti_sn_link_training(struct ti_sn65dsi86 *pdata, int dp_rate_idx,
>  		goto exit;
>  	}
>  
> +	/*
> +	 * eDP panels use an Alternate Scrambler Seed compared to displays
> +	 * hooked up via a full DisplayPort connector. SN65DSI86 only supports
> +	 * the alternate scrambler seed, not the normal one, so the only way we
> +	 * can support full DisplayPort displays is by fully turning off the
> +	 * scrambler.
> +	 */
> +	if (pdata->bridge.type == DRM_MODE_CONNECTOR_DisplayPort)
> +		regmap_update_bits(pdata->regmap, SN_TRAINING_SETTING_REG,
> +				   SCRAMBLE_DISABLE, SCRAMBLE_DISABLE);
> +
>  	/*
>  	 * We'll try to link train several times.  As part of link training
>  	 * the bridge chip will write DP_SET_POWER_D0 to DP_SET_POWER.  If
> @@ -1046,12 +1060,13 @@ static void ti_sn_bridge_atomic_enable(struct drm_bridge *bridge,
>  
>  	/*
>  	 * The SN65DSI86 only supports ASSR Display Authentication method and
> -	 * this method is enabled by default. An eDP panel must support this
> +	 * this method is enabled for eDP panels. An eDP panel must support this
>  	 * authentication method. We need to enable this method in the eDP panel
>  	 * at DisplayPort address 0x0010A prior to link training.
>  	 */
> -	drm_dp_dpcd_writeb(&pdata->aux, DP_EDP_CONFIGURATION_SET,
> -			   DP_ALTERNATE_SCRAMBLER_RESET_ENABLE);
> +	if (pdata->bridge.type == DRM_MODE_CONNECTOR_eDP)
> +		drm_dp_dpcd_writeb(&pdata->aux, DP_EDP_CONFIGURATION_SET,
> +				   DP_ALTERNATE_SCRAMBLER_RESET_ENABLE);
>  
>  	/* Set the DP output format (18 bpp or 24 bpp) */
>  	val = (ti_sn_bridge_get_bpp(old_bridge_state) == 18) ? BPP_18_RGB : 0;
> @@ -1215,6 +1230,8 @@ static int ti_sn_bridge_probe(struct auxiliary_device *adev,
>  
>  	pdata->bridge.funcs = &ti_sn_bridge_funcs;
>  	pdata->bridge.of_node = np;
> +	pdata->bridge.type = pdata->next_bridge->type == DRM_MODE_CONNECTOR_DisplayPort
> +			   ? DRM_MODE_CONNECTOR_DisplayPort : DRM_MODE_CONNECTOR_eDP;
>  
>  	drm_bridge_add(&pdata->bridge);
>  

-- 
Regards,

Laurent Pinchart