Re: [PATCH 2/2] drm/bridge: tc358767: Add configurable default preemphasis

[Alexander Stein <alexander.stein@ew.tq-group.com>]

Hi Marek,

Am Freitag, 31. Mai 2024, 22:42:04 CEST schrieb Marek Vasut:
> Make the default DP port preemphasis configurable via new DT property
> "toshiba,pre-emphasis". This is useful in case the DP link properties
> are known and starting link training from preemphasis setting of 0 dB
> is not useful. The preemphasis can be set separately for both DP lanes
> in range 0=0dB, 1=3.5dB, 2=6dB .
> 
> Signed-off-by: Marek Vasut <marex@denx.de>
> ---
> Cc: Andrzej Hajda <andrzej.hajda@intel.com>
> Cc: Conor Dooley <conor+dt@kernel.org>
> Cc: Daniel Vetter <daniel@ffwll.ch>
> Cc: David Airlie <airlied@gmail.com>
> Cc: Jernej Skrabec <jernej.skrabec@gmail.com>
> Cc: Jonas Karlman <jonas@kwiboo.se>
> Cc: Krzysztof Kozlowski <krzk+dt@kernel.org>
> Cc: Laurent Pinchart <Laurent.pinchart@ideasonboard.com>
> Cc: Lucas Stach <l.stach@pengutronix.de>
> Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
> Cc: Maxime Ripard <mripard@kernel.org>
> Cc: Neil Armstrong <neil.armstrong@linaro.org>
> Cc: Rob Herring <robh@kernel.org>
> Cc: Robert Foss <rfoss@kernel.org>
> Cc: Thomas Zimmermann <tzimmermann@suse.de>
> Cc: devicetree@vger.kernel.org
> Cc: dri-devel@lists.freedesktop.org
> Cc: kernel@dh-electronics.com
> ---
>  drivers/gpu/drm/bridge/tc358767.c | 49 ++++++++++++++++++++++++++-----
>  1 file changed, 42 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/gpu/drm/bridge/tc358767.c b/drivers/gpu/drm/bridge/tc358767.c
> index 1243918320a7d..32639865fea07 100644
> --- a/drivers/gpu/drm/bridge/tc358767.c
> +++ b/drivers/gpu/drm/bridge/tc358767.c
> @@ -241,6 +241,10 @@
>  
>  /* Link Training */
>  #define DP0_SRCCTRL		0x06a0
> +#define DP0_SRCCTRL_PRE1		GENMASK(29, 28)
> +#define DP0_SRCCTRL_SWG1		GENMASK(25, 24)
> +#define DP0_SRCCTRL_PRE0		GENMASK(21, 20)
> +#define DP0_SRCCTRL_SWG0		GENMASK(17, 16)
>  #define DP0_SRCCTRL_SCRMBLDIS		BIT(13)
>  #define DP0_SRCCTRL_EN810B		BIT(12)
>  #define DP0_SRCCTRL_NOTP		(0 << 8)
> @@ -278,6 +282,8 @@
>  #define AUDIFDATA6		0x0720	/* DP0 Audio Info Frame Bytes 27 to 24 */
>  
>  #define DP1_SRCCTRL		0x07a0	/* DP1 Control Register */
> +#define DP1_SRCCTRL_PRE			GENMASK(21, 20)
> +#define DP1_SRCCTRL_SWG			GENMASK(17, 16)
>  
>  /* PHY */
>  #define DP_PHY_CTRL		0x0800
> @@ -369,6 +375,7 @@ struct tc_data {
>  
>  	u32			rev;
>  	u8			assr;
> +	u8			pre_emphasis[2];
>  
>  	struct gpio_desc	*sd_gpio;
>  	struct gpio_desc	*reset_gpio;
> @@ -1090,13 +1097,17 @@ static int tc_main_link_enable(struct tc_data *tc)
>  			return ret;
>  	}
>  
> -	ret = regmap_write(tc->regmap, DP0_SRCCTRL, tc_srcctrl(tc));
> +	ret = regmap_write(tc->regmap, DP0_SRCCTRL,
> +			   tc_srcctrl(tc) |
> +			   FIELD_PREP(DP0_SRCCTRL_PRE0, tc->pre_emphasis[0]) |
> +			   FIELD_PREP(DP0_SRCCTRL_PRE1, tc->pre_emphasis[1]));
>  	if (ret)
>  		return ret;
>  	/* SSCG and BW27 on DP1 must be set to the same as on DP0 */
>  	ret = regmap_write(tc->regmap, DP1_SRCCTRL,
>  		 (tc->link.spread ? DP0_SRCCTRL_SSCG : 0) |
> -		 ((tc->link.rate != 162000) ? DP0_SRCCTRL_BW27 : 0));
> +		 ((tc->link.rate != 162000) ? DP0_SRCCTRL_BW27 : 0) |
> +		 FIELD_PREP(DP1_SRCCTRL_PRE, tc->pre_emphasis[1]));
>  	if (ret)
>  		return ret;
>  
> @@ -1188,8 +1199,10 @@ static int tc_main_link_enable(struct tc_data *tc)
>  		goto err_dpcd_write;
>  
>  	/* Reset voltage-swing & pre-emphasis */
> -	tmp[0] = tmp[1] = DP_TRAIN_VOLTAGE_SWING_LEVEL_0 |
> -			  DP_TRAIN_PRE_EMPH_LEVEL_0;
> +	tmp[0] = DP_TRAIN_VOLTAGE_SWING_LEVEL_0 |
> +		 FIELD_PREP(DP_TRAIN_PRE_EMPHASIS_MASK, tc->pre_emphasis[0]);
> +	tmp[1] = DP_TRAIN_VOLTAGE_SWING_LEVEL_0 |
> +		 FIELD_PREP(DP_TRAIN_PRE_EMPHASIS_MASK, tc->pre_emphasis[1]);
>  	ret = drm_dp_dpcd_write(aux, DP_TRAINING_LANE0_SET, tmp, 2);
>  	if (ret < 0)
>  		goto err_dpcd_write;
> @@ -1213,7 +1226,9 @@ static int tc_main_link_enable(struct tc_data *tc)
>  	ret = regmap_write(tc->regmap, DP0_SRCCTRL,
>  			   tc_srcctrl(tc) | DP0_SRCCTRL_SCRMBLDIS |
>  			   DP0_SRCCTRL_AUTOCORRECT |
> -			   DP0_SRCCTRL_TP1);
> +			   DP0_SRCCTRL_TP1 |
> +			   FIELD_PREP(DP0_SRCCTRL_PRE0, tc->pre_emphasis[0]) |
> +			   FIELD_PREP(DP0_SRCCTRL_PRE1, tc->pre_emphasis[1]));
>  	if (ret)
>  		return ret;
>  
> @@ -1248,7 +1263,9 @@ static int tc_main_link_enable(struct tc_data *tc)
>  	ret = regmap_write(tc->regmap, DP0_SRCCTRL,
>  			   tc_srcctrl(tc) | DP0_SRCCTRL_SCRMBLDIS |
>  			   DP0_SRCCTRL_AUTOCORRECT |
> -			   DP0_SRCCTRL_TP2);
> +			   DP0_SRCCTRL_TP2 |
> +			   FIELD_PREP(DP0_SRCCTRL_PRE0, tc->pre_emphasis[0]) |
> +			   FIELD_PREP(DP0_SRCCTRL_PRE1, tc->pre_emphasis[1]));
>  	if (ret)
>  		return ret;
>  
> @@ -1274,7 +1291,9 @@ static int tc_main_link_enable(struct tc_data *tc)
>  
>  	/* Clear Training Pattern, set AutoCorrect Mode = 1 */
>  	ret = regmap_write(tc->regmap, DP0_SRCCTRL, tc_srcctrl(tc) |
> -			   DP0_SRCCTRL_AUTOCORRECT);
> +			   DP0_SRCCTRL_AUTOCORRECT |
> +			   FIELD_PREP(DP0_SRCCTRL_PRE0, tc->pre_emphasis[0]) |
> +			   FIELD_PREP(DP0_SRCCTRL_PRE1, tc->pre_emphasis[1]));
>  	if (ret)
>  		return ret;
>  
> @@ -2346,6 +2365,7 @@ static int tc_probe_dpi_bridge_endpoint(struct tc_data *tc)
>  static int tc_probe_edp_bridge_endpoint(struct tc_data *tc)
>  {
>  	struct device *dev = tc->dev;
> +	struct device_node *port;
>  	struct drm_panel *panel;
>  	int ret;
>  
> @@ -2372,6 +2392,21 @@ static int tc_probe_edp_bridge_endpoint(struct tc_data *tc)
>  		tc->bridge.ops |= DRM_BRIDGE_OP_DETECT;
>  	tc->bridge.ops |= DRM_BRIDGE_OP_EDID;
>  
> +	port = of_graph_get_port_by_id(dev->of_node, 2);
> +	if (!port)
> +		return 0;
> +
> +	of_property_read_u8_array(port, "toshiba,pre-emphasis",
> +				  tc->pre_emphasis,
> +				  ARRAY_SIZE(tc->pre_emphasis));

This doesn't match the bindings. Bindings say it's a property of the
endpoint, not the port. Additionally it's uint32-array, not uint8-array.

Best regards,
Alexander

> +	of_node_put(port);
> +
> +	if (tc->pre_emphasis[0] < 0 || tc->pre_emphasis[0] > 2 ||
> +	    tc->pre_emphasis[1] < 0 || tc->pre_emphasis[1] > 2) {
> +		dev_err(dev, "Incorrect Pre-Emphasis setting, use either 0=0dB 1=3.5dB 2=6dB\n");
> +		return -EINVAL;
> +	}
> +
>  	return 0;
>  }
>  
> 


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