linux-kernel - Re: [Intel-gfx] [PATCH 3/3] drm/i915: Support DDI lane reversal for DP

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Message-ID: <55B88E25.6000006@intel.com>
Date:	Wed, 29 Jul 2015 13:56:13 +0530
From:	Sivakumar Thulasimani <sivakumar.thulasimani@...el.com>
To:	Benjamin Tissoires <benjamin.tissoires@...hat.com>,
	Daniel Vetter <daniel.vetter@...el.com>
CC:	intel-gfx@...ts.freedesktop.org, Todd Broch <tbroch@...omium.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [Intel-gfx] [PATCH 3/3] drm/i915: Support DDI lane reversal for
 DP

why not detect reverse in intel_dp_detect/intel_hpd_pulse ? that way you 
can identify both lane count and reversal state without touching 
anything in the link training code. i am yet to upstream my changes for 
CHT that i can share if required that does the same in intel_dp_detect 
without touching any line in link training path.

On 7/28/2015 9:33 PM, Benjamin Tissoires wrote:
> The DP outputs connected through a USB Type-C port can have inverted
> lanes. To detect that case, we implement autodetection by training only
> the first lane if it doesn't work, we assume that we need to invert
> the lanes.
>
> Tested on a Chromebook Pixel 2015 (samus) with a USB Type-C to HDMI
> adapter and a Dell 4K and some various regular monitors.
>
> Based on 2 patches from the ChromeOS tree by:
> Stéphane Marchesin <marcheu@...omium.org>
> Todd Broch <tbroch@...omium.org>
>
> Signed-off-by: Benjamin Tissoires <benjamin.tissoires@...hat.com>
> ---
>   drivers/gpu/drm/i915/intel_ddi.c | 13 +++++++++++++
>   drivers/gpu/drm/i915/intel_dp.c  | 36 ++++++++++++++++++++++++++++++++++++
>   drivers/gpu/drm/i915/intel_drv.h |  1 +
>   3 files changed, 50 insertions(+)
>
> diff --git a/drivers/gpu/drm/i915/intel_ddi.c b/drivers/gpu/drm/i915/intel_ddi.c
> index 9a40bfb..0b0c1ec 100644
> --- a/drivers/gpu/drm/i915/intel_ddi.c
> +++ b/drivers/gpu/drm/i915/intel_ddi.c
> @@ -2249,6 +2249,7 @@ static void intel_ddi_pre_enable(struct intel_encoder *intel_encoder)
>   	enum port port = intel_ddi_get_encoder_port(intel_encoder);
>   	int type = intel_encoder->type;
>   	int hdmi_level;
> +	bool reversed = false;
>   
>   	if (type == INTEL_OUTPUT_EDP) {
>   		struct intel_dp *intel_dp = enc_to_intel_dp(encoder);
> @@ -2295,8 +2296,20 @@ static void intel_ddi_pre_enable(struct intel_encoder *intel_encoder)
>   	if (type == INTEL_OUTPUT_DISPLAYPORT || type == INTEL_OUTPUT_EDP) {
>   		struct intel_dp *intel_dp = enc_to_intel_dp(encoder);
>   
> +		if (IS_BROADWELL(dev) && type == INTEL_OUTPUT_DISPLAYPORT) {
> +			intel_ddi_init_dp_buf_reg(intel_encoder);
> +			reversed = intel_dp_is_reversed(intel_dp);
> +		}
> +
>   		intel_ddi_init_dp_buf_reg(intel_encoder);
>   
> +		if (IS_BROADWELL(dev)) {
> +			if (reversed)
> +				intel_dp->DP |= DDI_BUF_PORT_REVERSAL;
> +			else
> +				intel_dp->DP &= ~DDI_BUF_PORT_REVERSAL;
> +		}
> +
>   		intel_dp_sink_dpms(intel_dp, DRM_MODE_DPMS_ON);
>   		intel_dp_start_link_train(intel_dp);
>   		intel_dp_complete_link_train(intel_dp);
> diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
> index b740987..18280cc 100644
> --- a/drivers/gpu/drm/i915/intel_dp.c
> +++ b/drivers/gpu/drm/i915/intel_dp.c
> @@ -3820,6 +3820,42 @@ intel_dp_complete_link_train(struct intel_dp *intel_dp)
>   		intel_dp->DP = DP;
>   }
>   
> +bool intel_dp_is_reversed(struct intel_dp *intel_dp)
> +{
> +	struct drm_encoder *encoder = &dp_to_dig_port(intel_dp)->base.base;
> +	struct drm_device *dev = encoder->dev;
> +	struct drm_i915_private *dev_priv = dev->dev_private;
> +	uint32_t DP = intel_dp->DP;
> +
> +	/*
> +	 * Train with 1 lane. There is no guarantee that the monitor supports
> +	 * 2 or 4 lanes, and we wouldn't see any asymetricity with 4 lanes.
> +	 */
> +	const uint8_t lane_count = 1;
> +	bool reversed;
> +
> +	if (!HAS_DDI(dev))
> +		return false;
> +
> +	DP &= ~(DDI_BUF_PORT_REVERSAL | DDI_PORT_WIDTH(4));
> +	DP |= DDI_PORT_WIDTH(lane_count);
> +
> +	I915_WRITE(intel_dp->output_reg, DP);
> +	POSTING_READ(intel_dp->output_reg);
> +	udelay(600);
> +
> +	if (!_intel_dp_start_link_train(intel_dp, lane_count, &DP, true))
> +		return true;
> +
> +	reversed = !_intel_dp_complete_link_train(intel_dp, lane_count, &DP, true);
> +
> +	/* clear training, we had only one lane */
> +	intel_dp->train_set_valid = false;
> +
> +	return reversed;
> +
> +}
> +
>   void intel_dp_stop_link_train(struct intel_dp *intel_dp)
>   {
>   	intel_dp_set_link_train(intel_dp, &intel_dp->DP,
> diff --git a/drivers/gpu/drm/i915/intel_drv.h b/drivers/gpu/drm/i915/intel_drv.h
> index 320c9e6..cba00c6 100644
> --- a/drivers/gpu/drm/i915/intel_drv.h
> +++ b/drivers/gpu/drm/i915/intel_drv.h
> @@ -1169,6 +1169,7 @@ int intel_dp_sink_crc(struct intel_dp *intel_dp, u8 *crc);
>   bool intel_dp_compute_config(struct intel_encoder *encoder,
>   			     struct intel_crtc_state *pipe_config);
>   bool intel_dp_is_edp(struct drm_device *dev, enum port port);
> +bool intel_dp_is_reversed(struct intel_dp *intel_dp);
>   enum irqreturn intel_dp_hpd_pulse(struct intel_digital_port *intel_dig_port,
>   				  bool long_hpd);
>   void intel_edp_backlight_on(struct intel_dp *intel_dp);

-- 
regards,
Sivakumar

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