ALSA: Add helper function for intersecting two rate masks

A bit of special care is necessary when creating the intersection of two rate
masks. This comes from the special meaning of the SNDRV_PCM_RATE_CONTINUOUS and
SNDRV_PCM_RATE_KNOT bits, which needs special handling when intersecting two
rate masks. SNDRV_PCM_RATE_CONTINUOUS means the hardware supports all rates in a
specific interval. SNDRV_PCM_RATE_KNOT means the hardware supports a set of
discrete rates specified by a list constraint. For all other cases the supported
rates are specified directly in the rate mask.

Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
Reviewed-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Mark Brown <broonie@linaro.org>

2 files changed, 41 insertions, 0 deletions

diff --git a/include/sound/pcm.h b/include/sound/pcm.h
index 84b10f9a2832..d0170913374d 100644
--- a/include/sound/pcm.h
+++ b/include/sound/pcm.h
@@ -901,6 +901,8 @@ extern const struct snd_pcm_hw_constraint_list snd_pcm_known_rates;
 int snd_pcm_limit_hw_rates(struct snd_pcm_runtime *runtime);
 unsigned int snd_pcm_rate_to_rate_bit(unsigned int rate);
 unsigned int snd_pcm_rate_bit_to_rate(unsigned int rate_bit);
+unsigned int snd_pcm_rate_mask_intersect(unsigned int rates_a,
+                                         unsigned int rates_b);
 
 static inline void snd_pcm_set_runtime_buffer(struct snd_pcm_substream *substream,
                                               struct snd_dma_buffer *bufp)
diff --git a/sound/core/pcm_misc.c b/sound/core/pcm_misc.c
index 43f24cce3dec..4560ca0e5651 100644
--- a/sound/core/pcm_misc.c
+++ b/sound/core/pcm_misc.c
@@ -514,3 +514,42 @@ unsigned int snd_pcm_rate_bit_to_rate(unsigned int rate_bit)
         return 0;
 }
 EXPORT_SYMBOL(snd_pcm_rate_bit_to_rate);
+
+static unsigned int snd_pcm_rate_mask_sanitize(unsigned int rates)
+{
+        if (rates & SNDRV_PCM_RATE_CONTINUOUS)
+                return SNDRV_PCM_RATE_CONTINUOUS;
+        else if (rates & SNDRV_PCM_RATE_KNOT)
+                return SNDRV_PCM_RATE_KNOT;
+        return rates;
+}
+
+/**
+ * snd_pcm_rate_mask_intersect - computes the intersection between two rate masks
+ * @rates_a: The first rate mask
+ * @rates_b: The second rate mask
+ *
+ * This function computes the rates that are supported by both rate masks passed
+ * to the function. It will take care of the special handling of
+ * SNDRV_PCM_RATE_CONTINUOUS and SNDRV_PCM_RATE_KNOT.
+ *
+ * Return: A rate mask containing the rates that are supported by both rates_a
+ * and rates_b.
+ */
+unsigned int snd_pcm_rate_mask_intersect(unsigned int rates_a,
+        unsigned int rates_b)
+{
+        rates_a = snd_pcm_rate_mask_sanitize(rates_a);
+        rates_b = snd_pcm_rate_mask_sanitize(rates_b);
+
+        if (rates_a & SNDRV_PCM_RATE_CONTINUOUS)
+                return rates_b;
+        else if (rates_b & SNDRV_PCM_RATE_CONTINUOUS)
+                return rates_a;
+        else if (rates_a & SNDRV_PCM_RATE_KNOT)
+                return rates_b;
+        else if (rates_b & SNDRV_PCM_RATE_KNOT)
+                return rates_a;
+        return rates_a & rates_b;
+}
+EXPORT_SYMBOL_GPL(snd_pcm_rate_mask_intersect);