Re: [RFC PATCH 2/2] drm/i915/bxt: Adjusting the error in horizontal timings retrieval

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

On Wed, 27 Apr 2016, Ville Syrjälä <ville.syrjala@linux.intel.com> wrote:
> On Tue, Apr 19, 2016 at 01:48:14PM +0530, Ramalingam C wrote:
>> In BXT DSI there is no regs programmed with few horizontal timings
>> in Pixels but txbyteclkhs.. So retrieval process adds some
>> ROUND_UP ERRORS in the process of PIXELS<==>txbyteclkhs.
>> 
>> Actually here for the given adjusted_mode, we are calculating the
>> value programmed to the port and then back to the horizontal timing
>> param in pixels. This is the expected value at the end of get_config,
>> including roundup errors. And if that is same as retrieved value
>> from port, then retrieved (HW state) adjusted_mode's horizontal
>> timings are corrected to match with SW state to nullify the errors.
>> 
>> Signed-off-by: Ramalingam C <ramalingam.c@intel.com>
>> ---
>>  drivers/gpu/drm/i915/intel_dsi.c |   97 ++++++++++++++++++++++++++++++++++----
>>  1 file changed, 88 insertions(+), 9 deletions(-)
>> 
>> diff --git a/drivers/gpu/drm/i915/intel_dsi.c b/drivers/gpu/drm/i915/intel_dsi.c
>> index e0259e6..8a1b872 100644
>> --- a/drivers/gpu/drm/i915/intel_dsi.c
>> +++ b/drivers/gpu/drm/i915/intel_dsi.c
>> @@ -46,6 +46,14 @@ static const struct {
>>  	},
>>  };
>>  
>> +/* return pixels in terms of txbyteclkhs */
>> +static u16 txbyteclkhs(u16 pixels, int bpp, int lane_count,
>> +		       u16 burst_mode_ratio)
>> +{
>> +	return DIV_ROUND_UP(DIV_ROUND_UP(pixels * bpp * burst_mode_ratio,
>> +					 8 * 100), lane_count);
>> +}
>> +
>>  /* return pixels equvalent to txbyteclkhs */
>>  static u16 pixels_from_txbyteclkhs(u16 clk_hs, int bpp, int lane_count,
>>  			u16 burst_mode_ratio)
>> @@ -779,11 +787,19 @@ static void bxt_dsi_get_pipe_config(struct intel_encoder *encoder,
>>  	struct drm_i915_private *dev_priv = dev->dev_private;
>>  	struct drm_display_mode *adjusted_mode =
>>  					&pipe_config->base.adjusted_mode;
>> +	struct drm_display_mode *adjusted_mode_sw;
>> +	struct intel_crtc *intel_crtc;
>>  	struct intel_dsi *intel_dsi = enc_to_intel_dsi(&encoder->base);
>>  	unsigned int lane_count = intel_dsi->lane_count;
>>  	unsigned int bpp, fmt;
>>  	enum port port;
>>  	u16 hactive, hfp, hsync, hbp, vfp, vsync, vbp;
>> +	u16 hfp_sw, hsync_sw, hbp_sw;
>> +	u16 crtc_htotal_sw, crtc_hsync_start_sw, crtc_hsync_end_sw,
>> +				crtc_hblank_start_sw, crtc_hblank_end_sw;
>> +
>> +	intel_crtc = to_intel_crtc(encoder->base.crtc);
>> +	adjusted_mode_sw = &intel_crtc->config->base.adjusted_mode;
>>
>  
>>  	/*
>>  	 * Atleast one port is active as encoder->get_config called only if
>> @@ -847,8 +863,79 @@ static void bxt_dsi_get_pipe_config(struct intel_encoder *encoder,
>>  	adjusted_mode->crtc_vsync_end = vsync + adjusted_mode->crtc_vsync_start;
>>  	adjusted_mode->crtc_vblank_start = adjusted_mode->crtc_vdisplay;
>>  	adjusted_mode->crtc_vblank_end = adjusted_mode->crtc_vtotal;
>> -}
>>  
>> +	/*
>> +	 * In BXT DSI there is no regs programmed with few horizontal timings
>> +	 * in Pixels but txbyteclkhs.. So retrieval process adds some
>> +	 * ROUND_UP ERRORS in the process of PIXELS<==>txbyteclkhs.
>> +	 * Actually here for the given adjusted_mode, we are calculating the
>> +	 * value programmed to the port and then back to the horizontal timing
>> +	 * param in pixels. This is the expected value, including roundup errors
>> +	 * And if that is same as retrieved value from port, then
>> +	 * (HW state) adjusted_mode's horizontal timings are corrected to
>> +	 * match with SW state to nullify the errors.
>> +	 */
>> +	/* Calculating the value programmed to the Port register */
>> +	hfp_sw = adjusted_mode_sw->crtc_hsync_start -
>> +					adjusted_mode_sw->crtc_hdisplay;
>> +	hsync_sw = adjusted_mode_sw->crtc_hsync_end -
>> +					adjusted_mode_sw->crtc_hsync_start;
>> +	hbp_sw = adjusted_mode_sw->crtc_htotal -
>> +					adjusted_mode_sw->crtc_hsync_end;
>
> So during the initial state readout we get passed crtc->config as
> pipe_config, and so we'll end up comparing the thing with itself. That
> should be fine. A bit of extra care is needed to make sure we don't use
> anything from crtc->config before we've filled it out with something,
> but looks like the code does things in the right order (given the
> previous patch which fills out all the htimings with something).
>
> I think the biggest issue with this patch is seeing the forest from the
> trees. Some refactoring would be good so that we'd have some kind of
> htimings_{to,from}_txbyteclkhs() functions instead of duplicating the
> same code multiple times.

Agreed. However, I opted to push them as-is as they fix the boot hang,
and leave the refactoring as follow-up.

BR,
Jani.


>
> So while it does look quite strange to be using crtc->config in the
> .get_config() I think it should work out.
>
> Acked-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
>
>> +
>> +	if (intel_dsi->dual_link) {
>> +		hfp_sw /= 2;
>> +		hsync_sw /= 2;
>> +		hbp_sw /= 2;
>> +	}
>> +
>> +	hfp_sw = txbyteclkhs(hfp_sw, bpp, lane_count,
>> +						intel_dsi->burst_mode_ratio);
>> +	hsync_sw = txbyteclkhs(hsync_sw, bpp, lane_count,
>> +			    intel_dsi->burst_mode_ratio);
>> +	hbp_sw = txbyteclkhs(hbp_sw, bpp, lane_count,
>> +						intel_dsi->burst_mode_ratio);
>> +
>> +	/* Reverse calculating the adjusted mode parameters from port reg vals*/
>> +	hfp_sw = pixels_from_txbyteclkhs(hfp_sw, bpp, lane_count,
>> +						intel_dsi->burst_mode_ratio);
>> +	hsync_sw = pixels_from_txbyteclkhs(hsync_sw, bpp, lane_count,
>> +						intel_dsi->burst_mode_ratio);
>> +	hbp_sw = pixels_from_txbyteclkhs(hbp_sw, bpp, lane_count,
>> +						intel_dsi->burst_mode_ratio);
>> +
>> +	if (intel_dsi->dual_link) {
>> +		hfp_sw *= 2;
>> +		hsync_sw *= 2;
>> +		hbp_sw *= 2;
>> +	}
>> +
>> +	crtc_htotal_sw = adjusted_mode_sw->crtc_hdisplay + hfp_sw +
>> +							hsync_sw + hbp_sw;
>> +	crtc_hsync_start_sw = hfp_sw + adjusted_mode_sw->crtc_hdisplay;
>> +	crtc_hsync_end_sw = hsync_sw + crtc_hsync_start_sw;
>> +	crtc_hblank_start_sw = adjusted_mode_sw->crtc_hdisplay;
>> +	crtc_hblank_end_sw = crtc_htotal_sw;
>> +
>> +	if (adjusted_mode->crtc_htotal == crtc_htotal_sw)
>> +		adjusted_mode->crtc_htotal = adjusted_mode_sw->crtc_htotal;
>> +
>> +	if (adjusted_mode->crtc_hsync_start == crtc_hsync_start_sw)
>> +		adjusted_mode->crtc_hsync_start =
>> +					adjusted_mode_sw->crtc_hsync_start;
>> +
>> +	if (adjusted_mode->crtc_hsync_end == crtc_hsync_end_sw)
>> +		adjusted_mode->crtc_hsync_end =
>> +					adjusted_mode_sw->crtc_hsync_end;
>> +
>> +	if (adjusted_mode->crtc_hblank_start == crtc_hblank_start_sw)
>> +		adjusted_mode->crtc_hblank_start =
>> +					adjusted_mode_sw->crtc_hblank_start;
>> +
>> +	if (adjusted_mode->crtc_hblank_end == crtc_hblank_end_sw)
>> +		adjusted_mode->crtc_hblank_end =
>> +					adjusted_mode_sw->crtc_hblank_end;
>> +}
>>  
>>  static void intel_dsi_get_config(struct intel_encoder *encoder,
>>  				 struct intel_crtc_state *pipe_config)
>> @@ -917,14 +1004,6 @@ static u16 txclkesc(u32 divider, unsigned int us)
>>  	}
>>  }
>>  
>> -/* return pixels in terms of txbyteclkhs */
>> -static u16 txbyteclkhs(u16 pixels, int bpp, int lane_count,
>> -		       u16 burst_mode_ratio)
>> -{
>> -	return DIV_ROUND_UP(DIV_ROUND_UP(pixels * bpp * burst_mode_ratio,
>> -					 8 * 100), lane_count);
>> -}
>> -
>>  static void set_dsi_timings(struct drm_encoder *encoder,
>>  			    const struct drm_display_mode *adjusted_mode)
>>  {
>> -- 
>> 1.7.9.5
>> _______________________________________________
>> Intel-gfx mailing list
>> Intel-gfx@lists.freedesktop.org
>> https://lists.freedesktop.org/mailman/listinfo/intel-gfx

-- 
Jani Nikula, Intel Open Source Technology Center
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