Re: [PATCH v2 2/4] drm/i915: implement set_ncts callback

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

On Mon, 10 Aug 2015, libin.yang@intel.com wrote:
> From: Libin Yang <libin.yang@intel.com>
>
> Display audio may not work at some frequencies
> with the HW provided N/CTS.
>
> This patch sets the proper N value for the
> given audio sample rate at the impacted frequencies.
> At other frequencies, it will use the N/CTS value
> which HW provides.
>
> Signed-off-by: Libin Yang <libin.yang@intel.com>
> ---
>  drivers/gpu/drm/i915/i915_reg.h    |  2 +
>  drivers/gpu/drm/i915/intel_audio.c | 95 ++++++++++++++++++++++++++++++++++++++
>  2 files changed, 97 insertions(+)
>
> diff --git a/drivers/gpu/drm/i915/i915_reg.h b/drivers/gpu/drm/i915/i915_reg.h
> index ea46d68..da2d128 100644
> --- a/drivers/gpu/drm/i915/i915_reg.h
> +++ b/drivers/gpu/drm/i915/i915_reg.h
> @@ -7014,6 +7014,8 @@ enum skl_disp_power_wells {
>  					_HSW_AUD_MISC_CTRL_A, \
>  					_HSW_AUD_MISC_CTRL_B)
>  
> +#define HSW_AUD_PIPE_CONN_SEL_CTRL  0x650ac

You're not using this register in this patch.

> +
>  #define _HSW_AUD_DIP_ELD_CTRL_ST_A	0x650b4
>  #define _HSW_AUD_DIP_ELD_CTRL_ST_B	0x651b4
>  #define HSW_AUD_DIP_ELD_CTRL(pipe) _PIPE(pipe, \
> diff --git a/drivers/gpu/drm/i915/intel_audio.c b/drivers/gpu/drm/i915/intel_audio.c
> index dc32cf4..eddf37f 100644
> --- a/drivers/gpu/drm/i915/intel_audio.c
> +++ b/drivers/gpu/drm/i915/intel_audio.c
> @@ -68,6 +68,30 @@ static const struct {
>  	{ 148500, AUD_CONFIG_PIXEL_CLOCK_HDMI_148500 },
>  };
>  
> +#define TMDS_297M 297000
> +#define TMDS_296M DIV_ROUND_UP(297000 * 1000, 1001)
> +static const struct {
> +	int sample_rate;
> +	int clock;
> +	int n;
> +	int cts;
> +} aud_ncts[] = {
> +	{ 44100, TMDS_296M, 4459, 234375 },
> +	{ 44100, TMDS_297M, 4704, 247500 },
> +	{ 48000, TMDS_296M, 5824, 281250 },
> +	{ 48000, TMDS_297M, 5120, 247500 },
> +	{ 32000, TMDS_296M, 5824, 421875 },
> +	{ 32000, TMDS_297M, 3072, 222750 },
> +	{ 88200, TMDS_296M, 8918, 234375 },
> +	{ 88200, TMDS_297M, 9408, 247500 },
> +	{ 96000, TMDS_296M, 11648, 281250 },
> +	{ 96000, TMDS_297M, 10240, 247500 },
> +	{ 176400, TMDS_296M, 17836, 234375 },
> +	{ 176400, TMDS_297M, 18816, 247500 },
> +	{ 44100, TMDS_296M, 23296, 281250 },
> +	{ 44100, TMDS_297M, 20480, 247500 },
> +};
> +
>  /* get AUD_CONFIG_PIXEL_CLOCK_HDMI_* value for mode */
>  static u32 audio_config_hdmi_pixel_clock(struct drm_display_mode *mode)
>  {
> @@ -514,12 +538,83 @@ static int i915_audio_component_get_cdclk_freq(struct device *dev)
>  	return ret;
>  }
>  
> +static int i915_audio_component_set_ncts(struct device *dev, int port,
> +			int dev_entry, int rate)
> +{
> +	struct drm_i915_private *dev_priv = dev_to_i915(dev);
> +	struct drm_device *drm_dev = dev_priv->dev;
> +	struct intel_encoder *intel_encoder;
> +	struct intel_digital_port *intel_dig_port;
> +	struct intel_crtc *crtc;
> +	struct drm_display_mode *mode;
> +	enum pipe pipe = -1;
> +	u32 tmp;
> +	int i;
> +	int n_low, n_up, n = 0;
> +
> +	/* 1. get the pipe */
> +	for_each_intel_encoder(drm_dev, intel_encoder) {
> +		intel_dig_port = enc_to_dig_port(&intel_encoder->base);
> +		if (port == intel_dig_port->port) {
> +			crtc = to_intel_crtc(intel_encoder->base.crtc);
> +			if (!crtc) {
> +				DRM_DEBUG_KMS("%s: crtc is NULL\n", __func__);
> +				continue;
> +			}
> +			pipe = crtc->pipe;
> +			break;
> +		}
> +	}
> +
> +	if (pipe == -1) {

INVALID_PIPE

> +		DRM_DEBUG_KMS("no pipe for the port %c\n", port_name(port));
> +		return -ENODEV;
> +	}
> +	DRM_DEBUG_KMS("pipe %c connects port %c\n",
> +				  pipe_name(pipe), port_name(port));
> +	mode = &crtc->config->base.adjusted_mode;
> +
> +	/* 2. Need set the N/CTS manually at some frequencies */
> +	if ((mode->clock != TMDS_297M) &&
> +		(mode->clock != TMDS_296M)) {
> +		tmp = I915_READ(HSW_AUD_CFG(pipe));
> +		tmp &= ~AUD_CONFIG_N_PROG_ENABLE;
> +		I915_WRITE(HSW_AUD_CFG(pipe), tmp);
> +		return 0;
> +	}

I'm thinking it would be better to always use the manual setting. There
may be obscure bugs due to *sometimes* using automatic mode and some
other times not. Or maybe we could use automatic mode in error
scenarios?

> +
> +	/* 3. calculate the N/CTS */
> +	for (i = 0; i < ARRAY_SIZE(aud_ncts); i++) {
> +		if ((rate == aud_ncts[i].sample_rate) &&
> +			(mode->clock == aud_ncts[i].clock)) {
> +			n = aud_ncts[i].n;
> +			break;
> +		}
> +	}

This part looks like a function to be abstracted (see
e.g. audio_config_hdmi_pixel_clock).

> +	if (n == 0)
> +		return 0;

This needs at least a debug warning and perhaps reverting to the
automatic mode.

> +	n_low = n & 0xfff;
> +	n_up = (n >> 12) & 0xff;
> +
> +	/* 4. set the N/CTS */
> +	tmp = I915_READ(HSW_AUD_CFG(pipe));
> +	tmp |= AUD_CONFIG_N_PROG_ENABLE;
> +	tmp &= ~AUD_CONFIG_UPPER_N_MASK;
> +	tmp |= (n_up << AUD_CONFIG_UPPER_N_SHIFT);
> +	tmp &= ~AUD_CONFIG_LOWER_N_MASK;
> +	tmp |= (n_low << AUD_CONFIG_LOWER_N_SHIFT);

You could squash the ors and ands together.

> +	I915_WRITE(HSW_AUD_CFG(pipe), tmp);
> +
> +	return 0;
> +}
> +
>  static const struct i915_audio_component_ops i915_audio_component_ops = {
>  	.owner		= THIS_MODULE,
>  	.get_power	= i915_audio_component_get_power,
>  	.put_power	= i915_audio_component_put_power,
>  	.codec_wake_override = i915_audio_component_codec_wake_override,
>  	.get_cdclk_freq	= i915_audio_component_get_cdclk_freq,
> +	.set_ncts = i915_audio_component_set_ncts,
>  };
>  
>  static int i915_audio_component_bind(struct device *i915_dev,
> -- 
> 1.9.1
>
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-- 
Jani Nikula, Intel Open Source Technology Center
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