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

Jani Nikula
2015-08-10T12:00:13Z

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