Re: [PATCH] drm/i915: add LG eDP panel to quirk database

[Jani Nikula <jani.nikula@intel.com>]

On Thu, 06 Sep 2018, "Lee, Shawn C" <shawn.c.lee@intel.com> wrote:
> The N value was computed by kernel driver that based on synchronous clock
> mode. But only specific N value (0x8000) would be acceptable for
> LG LP140WF6-SPM1 eDP panel which is running at asynchronous clock mode.

As I wrote before, it's the DP source that determines between
synchronous and asynchronous clock mode, not the sink. The sink in
question appears to expect a constant N related to asynchronous clock
mode even when we're using and advertising synchronous clock mode in DP
Main Stream Attributes.

(It's possible a certain other OS uses the same constant N regardless of
clock mode, leading to the panel working by coincidence.)

> With the other N value, Tcon will enter BITS mode and display black screen.
> Add this panel into quirk database and give particular N value when
> calculate M/N divider.
>
> Cc: Jani Nikula <jani.nikula@intel.com>
> Cc: Cooper Chiou <cooper.chiou@intel.com>
> Cc: Matt Atwood <matthew.s.atwood@intel.com>
> Signed-off-by: Lee, Shawn C <shawn.c.lee@intel.com>
> ---
>  drivers/gpu/drm/drm_dp_helper.c      | 10 +++++++++-
>  drivers/gpu/drm/i915/intel_display.c | 16 ++++++++++------
>  drivers/gpu/drm/i915/intel_display.h |  3 ++-
>  drivers/gpu/drm/i915/intel_dp.c      |  8 ++++++--
>  drivers/gpu/drm/i915/intel_dp_mst.c  |  2 +-
>  include/drm/drm_dp_helper.h          |  1 +
>  6 files changed, 29 insertions(+), 11 deletions(-)
>
> diff --git a/drivers/gpu/drm/drm_dp_helper.c b/drivers/gpu/drm/drm_dp_helper.c
> index 0cccbcb2d03e..a0259bbbe9df 100644
> --- a/drivers/gpu/drm/drm_dp_helper.c
> +++ b/drivers/gpu/drm/drm_dp_helper.c
> @@ -1258,13 +1258,18 @@ struct dpcd_quirk {
>  	u8 oui[3];
>  	bool is_branch;
>  	u32 quirks;
> +	u8 dev_id[6];

Your commit message says nothing about the need to extend the quirk
mechanism to use the device ID. Do we really need it?

If we do need it, please name it device_id like it is in struct
drm_dp_dpcd_ident, and place it after oui.

>  };
>  
>  #define OUI(first, second, third) { (first), (second), (third) }
> +#define DEVICE_ID(first, second, third, fourth, fifth, sixth) \
> +	{ (first), (second), (third), (fourth), (fifth), (sixth) }
>  
>  static const struct dpcd_quirk dpcd_quirk_list[] = {
>  	/* Analogix 7737 needs reduced M and N at HBR2 link rates */
> -	{ OUI(0x00, 0x22, 0xb9), true, BIT(DP_DPCD_QUIRK_LIMITED_M_N) },
> +	{ OUI(0x00, 0x22, 0xb9), true, BIT(DP_DPCD_QUIRK_LIMITED_M_N), DEVICE_ID(0, 0, 0, 0, 0, 0) },

Maybe add #define DEVICE_ID_ANY to initialize all to zero.

> +	/* LG LP140WF6-SPM1 eDP panel */
> +	{ OUI(0x00, 0x22, 0xb9), false, BIT(DP_DPCD_QUIRK_CONSTANT_N), DEVICE_ID('s', 'i', 'v', 'a', 'r', 'T') },
>  };
>  
>  #undef OUI

#undef DEVICE_ID
#undef DEVICE_ID_ANY

> @@ -1293,6 +1298,9 @@ drm_dp_get_quirks(const struct drm_dp_dpcd_ident *ident, bool is_branch)
>  		if (memcmp(quirk->oui, ident->oui, sizeof(ident->oui)) != 0)
>  			continue;
>  
> +		if (!is_branch && memcmp(quirk->dev_id, ident->device_id, 6) != 0)
> +			continue;
> +

Why not branch devices? This is really a trick to avoid matching on the
Analogix device which you set to zeros, and now you require device id
match for all non-branch quirks. Not good. Please check if the quirk
table has all zeros, and compare if not.

>  		quirks |= quirk->quirks;
>  	}
>  
> diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
> index ec3e24f07486..ff01a742b054 100644
> --- a/drivers/gpu/drm/i915/intel_display.c
> +++ b/drivers/gpu/drm/i915/intel_display.c
> @@ -6465,7 +6465,7 @@ static int ironlake_fdi_compute_config(struct intel_crtc *intel_crtc,
>  	pipe_config->fdi_lanes = lane;
>  
>  	intel_link_compute_m_n(pipe_config->pipe_bpp, lane, fdi_dotclock,
> -			       link_bw, &pipe_config->fdi_m_n, false);
> +			       link_bw, &pipe_config->fdi_m_n, false, false);

This is getting pretty ugly, to be honest. Which is why I was wondering
if we could actually turn the Analogix quirk into a constant N...

>  
>  	ret = ironlake_check_fdi_lanes(dev, intel_crtc->pipe, pipe_config);
>  	if (ret == -EINVAL && pipe_config->pipe_bpp > 6*3) {
> @@ -6680,7 +6680,7 @@ intel_reduce_m_n_ratio(uint32_t *num, uint32_t *den)
>  
>  static void compute_m_n(unsigned int m, unsigned int n,
>  			uint32_t *ret_m, uint32_t *ret_n,
> -			bool reduce_m_n)
> +			bool reduce_m_n, bool constant_n)
>  {
>  	/*
>  	 * Reduce M/N as much as possible without loss in precision. Several DP
> @@ -6695,7 +6695,11 @@ static void compute_m_n(unsigned int m, unsigned int n,
>  		}
>  	}
>  
> -	*ret_n = min_t(unsigned int, roundup_pow_of_two(n), DATA_LINK_N_MAX);
> +	if (constant_n)
> +		*ret_n = 0x8000;
> +	else
> +		*ret_n = min_t(unsigned int, roundup_pow_of_two(n), DATA_LINK_N_MAX);
> +
>  	*ret_m = div_u64((uint64_t) m * *ret_n, n);
>  	intel_reduce_m_n_ratio(ret_m, ret_n);
>  }
> @@ -6704,18 +6708,18 @@ void
>  intel_link_compute_m_n(int bits_per_pixel, int nlanes,
>  		       int pixel_clock, int link_clock,
>  		       struct intel_link_m_n *m_n,
> -		       bool reduce_m_n)
> +		       bool reduce_m_n, bool constant_n)
>  {
>  	m_n->tu = 64;
>  
>  	compute_m_n(bits_per_pixel * pixel_clock,
>  		    link_clock * nlanes * 8,
>  		    &m_n->gmch_m, &m_n->gmch_n,
> -		    reduce_m_n);
> +		    reduce_m_n, constant_n);
>  
>  	compute_m_n(pixel_clock, link_clock,
>  		    &m_n->link_m, &m_n->link_n,
> -		    reduce_m_n);
> +		    reduce_m_n, constant_n);
>  }
>  
>  static inline bool intel_panel_use_ssc(struct drm_i915_private *dev_priv)
> diff --git a/drivers/gpu/drm/i915/intel_display.h b/drivers/gpu/drm/i915/intel_display.h
> index 43f080c6538d..dde7d73bd36d 100644
> --- a/drivers/gpu/drm/i915/intel_display.h
> +++ b/drivers/gpu/drm/i915/intel_display.h
> @@ -379,7 +379,8 @@ struct intel_link_m_n {
>  void intel_link_compute_m_n(int bpp, int nlanes,
>  			    int pixel_clock, int link_clock,
>  			    struct intel_link_m_n *m_n,
> -			    bool reduce_m_n);
> +			    bool reduce_m_n,
> +			    bool constant_n);
>  
>  bool is_ccs_modifier(u64 modifier);
>  #endif
> diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
> index 436c22de33b6..95edbac24919 100644
> --- a/drivers/gpu/drm/i915/intel_dp.c
> +++ b/drivers/gpu/drm/i915/intel_dp.c
> @@ -2000,6 +2000,8 @@ intel_dp_compute_config(struct intel_encoder *encoder,
>  		to_intel_digital_connector_state(conn_state);
>  	bool reduce_m_n = drm_dp_has_quirk(&intel_dp->desc,
>  					   DP_DPCD_QUIRK_LIMITED_M_N);
> +	bool constant_n = drm_dp_has_quirk(&intel_dp->desc,
> +					   DP_DPCD_QUIRK_CONSTANT_N);
>  
>  	if (HAS_PCH_SPLIT(dev_priv) && !HAS_DDI(dev_priv) && port != PORT_A)
>  		pipe_config->has_pch_encoder = true;
> @@ -2064,7 +2066,8 @@ intel_dp_compute_config(struct intel_encoder *encoder,
>  			       adjusted_mode->crtc_clock,
>  			       pipe_config->port_clock,
>  			       &pipe_config->dp_m_n,
> -			       reduce_m_n);
> +			       reduce_m_n,
> +			       constant_n);
>  
>  	if (intel_connector->panel.downclock_mode != NULL &&
>  		dev_priv->drrs.type == SEAMLESS_DRRS_SUPPORT) {
> @@ -2074,7 +2077,8 @@ intel_dp_compute_config(struct intel_encoder *encoder,
>  					       intel_connector->panel.downclock_mode->clock,
>  					       pipe_config->port_clock,
>  					       &pipe_config->dp_m2_n2,
> -					       reduce_m_n);
> +					       reduce_m_n,
> +					       constant_n);
>  	}
>  
>  	if (!HAS_DDI(dev_priv))
> diff --git a/drivers/gpu/drm/i915/intel_dp_mst.c b/drivers/gpu/drm/i915/intel_dp_mst.c
> index 352e5216cc65..ac23982fa335 100644
> --- a/drivers/gpu/drm/i915/intel_dp_mst.c
> +++ b/drivers/gpu/drm/i915/intel_dp_mst.c
> @@ -87,7 +87,7 @@ static bool intel_dp_mst_compute_config(struct intel_encoder *encoder,
>  			       adjusted_mode->crtc_clock,
>  			       pipe_config->port_clock,
>  			       &pipe_config->dp_m_n,
> -			       reduce_m_n);
> +			       reduce_m_n, false);
>  
>  	pipe_config->dp_m_n.tu = slots;
>  
> diff --git a/include/drm/drm_dp_helper.h b/include/drm/drm_dp_helper.h
> index 05cc31b5db16..b1b2fd609c1c 100644
> --- a/include/drm/drm_dp_helper.h
> +++ b/include/drm/drm_dp_helper.h
> @@ -1266,6 +1266,7 @@ enum drm_dp_quirk {
>  	 * to 16 bits.
>  	 */
>  	DP_DPCD_QUIRK_LIMITED_M_N,
> +	DP_DPCD_QUIRK_CONSTANT_N,

Documentation missing. See the comment for limited M/N.

BR,
Jani.

>  };
>  
>  /**

-- 
Jani Nikula, Intel Open Source Graphics Center
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