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

["Lee, Shawn C" <shawn.c.lee@intel.com>]

On Thu, 06 Sep 2018, Jani Nikula 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.)
>

Yes, this sink device should not expect source will give specific N value. I have no idea what the other OS to calculate M/V value but vendor said they don't have similar issue before.

>> 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.
>

If we just recognize OUI. And didn't use device_id to identify which sink/branch device need specific M/N value. 
That means all the sink/branch device with Analogix OUI will apply this work around.

00-22-B9   (hex)		Analogix Seminconductor, Inc

>>  };
>>  
>>  #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.
>

It will not compare device_id for branch device because of I don't have the device_id for Analogix 7737 branch device you debug before. 
So I set it to zero for default setup.

>>  		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...
>

Seems Anaglogix 7737 can't handle full 24-bit main link Mdiv and Ndiv main link attributes properly. 
Using constant N (0x8000) value should be acceptable. It would not exceed the Analogix 7737 limitation.

>>  
>>  	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.
>

I think we can remain DP_DPCD_QUIRK_LIMITED_M_N only and give these 2 device the same N value.

>BR,
>Jani.
>
>>  };
>>  
>>  /**
>
>--
>Jani Nikula, Intel Open Source Graphics Center
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