Re: [alsa-devel] [PATCH RFC v2 10/13] sound/core: add DRM ELD helper

[Jyri Sarha <jyri.sarha@iki.fi>]

On 2015-04-02 12:22, Russell King wrote:
> Add a helper for the EDID like data structure, which is typically 
> passed
> from a HDMI adapter to its associated audio driver.  This informs the
> audio driver of the capabilities of the attached HDMI sink.
> 
> Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
> ---
>  include/sound/pcm_drm_eld.h |  6 +++
>  sound/core/Kconfig          |  3 ++
>  sound/core/Makefile         |  1 +
>  sound/core/pcm_drm_eld.c    | 92 
> +++++++++++++++++++++++++++++++++++++++++++++
>  4 files changed, 102 insertions(+)
>  create mode 100644 include/sound/pcm_drm_eld.h
>  create mode 100644 sound/core/pcm_drm_eld.c
> 
> diff --git a/include/sound/pcm_drm_eld.h b/include/sound/pcm_drm_eld.h
> new file mode 100644
> index 000000000000..93357b25d2e2
> --- /dev/null
> +++ b/include/sound/pcm_drm_eld.h
> @@ -0,0 +1,6 @@
> +#ifndef __SOUND_PCM_DRM_ELD_H
> +#define __SOUND_PCM_DRM_ELD_H
> +
> +int snd_pcm_hw_constraint_eld(struct snd_pcm_runtime *runtime, void 
> *eld);
> +
> +#endif
> diff --git a/sound/core/Kconfig b/sound/core/Kconfig
> index 313f22e9d929..b534c8a6046b 100644
> --- a/sound/core/Kconfig
> +++ b/sound/core/Kconfig
> @@ -6,6 +6,9 @@ config SND_PCM
>  	tristate
>  	select SND_TIMER
> 
> +config SND_PCM_ELD
> +	bool
> +
>  config SND_DMAENGINE_PCM
>  	tristate
> 
> diff --git a/sound/core/Makefile b/sound/core/Makefile
> index 4daf2f58261c..591b49157b4d 100644
> --- a/sound/core/Makefile
> +++ b/sound/core/Makefile
> @@ -13,6 +13,7 @@ snd-$(CONFIG_SND_JACK)	  += jack.o
>  snd-pcm-y := pcm.o pcm_native.o pcm_lib.o pcm_timer.o pcm_misc.o \
>  		pcm_memory.o memalloc.o
>  snd-pcm-$(CONFIG_SND_DMA_SGBUF) += sgbuf.o
> +snd-pcm-$(CONFIG_SND_PCM_ELD) += pcm_drm_eld.o
> 
>  # for trace-points
>  CFLAGS_pcm_lib.o := -I$(src)
> diff --git a/sound/core/pcm_drm_eld.c b/sound/core/pcm_drm_eld.c
> new file mode 100644
> index 000000000000..47d9b60435fe
> --- /dev/null
> +++ b/sound/core/pcm_drm_eld.c
> @@ -0,0 +1,92 @@
> +/*
> + *  PCM DRM helpers
> + *
> + *   This program is free software; you can redistribute it and/or 
> modify
> + *   it under the terms of the GNU General Public License version 2 as
> + *   published by the Free Software Foundation.
> + */
> +#include <linux/export.h>
> +#include <drm/drm_edid.h>
> +#include <sound/pcm.h>
> +#include <sound/pcm_drm_eld.h>
> +
> +static const unsigned int eld_rates[] = {
> +	32000,
> +	44100,
> +	48000,
> +	88200,
> +	96000,
> +	176400,
> +	192000,
> +};
> +

For what I can see, you are setting the cross dependency between
the sample rate and channels incorrectly. You should look for the
currently tested channel count directly from hw params.

> +static int eld_limit_rates(struct snd_pcm_hw_params *params,
> +			   struct snd_pcm_hw_rule *rule)
> +{
> +	struct snd_interval *r = hw_param_interval(params, rule->var);
> +	struct snd_interval *c;
> +	unsigned int rate_mask = 7, i;
> +	const u8 *sad, *eld = rule->private;
> +
> +	sad = drm_eld_sad(eld);
> +	if (sad) {
> +		c = hw_param_interval(params, SNDRV_PCM_HW_PARAM_CHANNELS);
-               c = hw_param_interval(params, 
SNDRV_PCM_HW_PARAM_CHANNELS);
+               uint pchannels = params_channels(params);
> +
> +		for (i = drm_eld_sad_count(eld); i > 0; i--, sad += 3) {
> +			unsigned channels = 1 + (sad[0] & 7);
> +
> +			/*
> +			 * Exclude SADs which do not include the
> +			 * requested number of channels.
> +			 */
> +			if (pchannels <= channels)
> +				rate_mask |= sad[1];
> +		}
> +printk("%s: r %d-%d c %d-%d m %x\n", __func__, r->min, r->max,
> c->min, c->max, rate_mask);
> +	}
> +
> +	return snd_interval_list(r, ARRAY_SIZE(eld_rates), eld_rates,
> +				 rate_mask);
> +}
> +

 From this side the dependency is missing all together.

> +static int eld_limit_channels(struct snd_pcm_hw_params *params,
> +			      struct snd_pcm_hw_rule *rule)
> +{
> +	struct snd_interval *var = hw_param_interval(params, rule->var);
> +	struct snd_interval t = { .min = 1, .max = 2, .integer = 1, };
> +	unsigned int i;

+       unsigned int j;

> +	const u8 *sad, *eld = rule->private;

+	int rate = params_rate(params);

> +
> +	sad = drm_eld_sad(eld);
> +	if (sad) {
> +		for (i = drm_eld_sad_count(eld); i > 0; i--, sad += 3) {

+                for (j = 0; j < ARRAY_SIZE(eld_rates); j++)
+                        if ((sad[1] & (1<<j)) && rate == eld_rates[j]) 
{

> +			 switch (sad[0] & 0x78) {
> +			 case 0x08:
> +				t.max = max(t.max, (sad[0] & 7) + 1u);
> +				break;
> +			}

+               }

> +		}
> +	}
> +
> +	return snd_interval_refine(var, &t);
> +}
> +

The code is completely untested, but I am sure you got the idea.

Best regards,
Jyri

> +int snd_pcm_hw_constraint_eld(struct snd_pcm_runtime *runtime, void 
> *eld)
> +{
> +	int ret;
> +
> +	ret = snd_pcm_hw_rule_add(runtime, 0, SNDRV_PCM_HW_PARAM_RATE,
> +				  eld_limit_rates, eld,
> +				  SNDRV_PCM_HW_PARAM_RATE,
> +				  SNDRV_PCM_HW_PARAM_CHANNELS, -1);
> +	if (ret < 0)
> +		return ret;
> +
> +	ret = snd_pcm_hw_rule_add(runtime, 0, SNDRV_PCM_HW_PARAM_CHANNELS,
> +				  eld_limit_channels, eld,
> +				  SNDRV_PCM_HW_PARAM_CHANNELS,
> +				  SNDRV_PCM_HW_PARAM_RATE, -1);
> +
> +	return ret;
> +}
> +EXPORT_SYMBOL_GPL(snd_pcm_hw_constraint_eld);