On Nov 14 2017 15:31, Kuninori Morimoto wrote:
From: Kuninori Morimoto <kuninori.morimoto.gx@xxxxxxxxxxx> Power Down Release Command (PMVR, PMDAC, RSTN, PMDA1-PMDA6) which are located on PW_MGMT1 / PW_MGMT3 register must be write again after at least 5 LRCK cycle or later from the first command. Otherwise, Playback volume will be 0dB. This patch adds dummy write when Playback Start timing. ... + + delay = 6000000 / priv->rate; + priv->component = &codec->component; + schedule_delayed_work(&priv->dummy_write_work, + usecs_to_jiffies(delay));
In my understanding, kernel's service of delayed work relies on kernel's timer service. Resolution of the service is quite coarse in this purpose, at least for several phases of word select clock. In the worst case when task scheduling is too delay, many audio samples are not presented by the DAC in the beginning of playback. I can easily imagine that users get confused.
For this purpose, hrtimer kernel service is better. However, in design of ALSA PCM core, .trigger callback can be done in any IRQ context, basically. This means that we can't call task scheduler in the callback as long as issuing the command in the callback. This is a reason that you use workqueue for this purpose.
In your patch description, 5 word select phases after 'the first command'. According to "Digital Attenuator" section per page 44 of AK4613 English datasheet (AsahiKASEI 2015, MS1052-E-05)[1], your 'the first command' seems to be the previous command issueing of 'power-down release command'. In my understanding, in ak4613 codec driver, issueing of the previous command is done in 'ak4613_set_bias_level()'. If there's a guarantee for DAPM stuffs to call this function on any non-IRQ context, it's better to call the subsequent commands in the function with interval of sleep functionality with finer resolution (e.g. usleep_range()) but I don't know exactly that any components has guarantee to receive word select clock when the function is called.
[1] http://www.akm.com/akm/en/file/datasheet/AK4613VQ.pdf Regards Takashi Sakamoto _______________________________________________ Alsa-devel mailing list Alsa-devel@xxxxxxxxxxxxxxxx http://mailman.alsa-project.org/mailman/listinfo/alsa-devel
