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From: "Troy Mitchell" <troy.mitchell@linux.spacemit.com>
To: "Bui Duc Phuc" <phucduc.bui@gmail.com>
Cc: "Yixun Lan" <dlan@kernel.org>, "Takashi Iwai" <tiwai@suse.com>,
	"Mark Brown" <broonie@kernel.org>,
	"Jaroslav Kysela" <perex@perex.cz>,
	"Liam Girdwood" <lgirdwood@gmail.com>,
	"Goko Mell" <goku.sonxin626@gmail.com>,
	"Jinmei Wei" <weijinmei@linux.spacemit.com>,
	"Kuninori Morimoto" <kuninori.morimoto.gx@renesas.com>,
	<linux-riscv@lists.infradead.org>, <spacemit@lists.linux.dev>,
	<linux-sound@vger.kernel.org>, <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] ASoC: spacemit: Remove redundant DAI field initialization
Date: Tue, 04 Aug 2026 02:59:36 -0700	[thread overview]
Message-ID: <DKG2L4V8Q2EU.1W5VODY60D6D7@linux.spacemit.com> (raw)
In-Reply-To: <CAABR9nFn0XW3CzAEncVkVKd65yBUEmquxjag6ybf_-NRf6mA8A@mail.gmail.com>

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> I traced the probe path and confirmed that snd_soc_dai_stream_valid()
> is called from soc_new_pcm().
> However, I still couldn't see where a nonzero channels_min alone leads
> to creating a capture substream
> without an RX DMA channel.
> To avoid confusion, I'm referring specifically to the DMA-based
> configuration, not PIO mode.
> Could you point me to the relevant call path?

More precisely, channels_min alone is not sufficient. The codec DAI must
also support capture (or be the dummy DAI for a dynamic link), and the link
must not be playback_only.

Under those conditions, the path is:

  soc_new_pcm()
    -> soc_get_playback_capture()
    -> soc_create_pcm(..., capture = 1)
    -> snd_pcm_new()
    -> snd_pcm_new_stream(CAPTURE, 1)
    -> snd_soc_pcm_component_new()
    -> dmaengine_pcm_new()

dmaengine_pcm_request_chan_of() tolerates a missing "rx" channel and leaves
pcm->chan[CAPTURE] NULL. Once the capture substream exists,
dmaengine_pcm_new() returns -EINVAL with
"Missing dma channel for stream: 1".
The conditional initialization prevents the CPU DAI from advertising that
direction for a tx-only node.

                                            - Troy

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WARNING: multiple messages have this Message-ID (diff)
From: "Troy Mitchell" <troy.mitchell@linux.spacemit.com>
To: "Bui Duc Phuc" <phucduc.bui@gmail.com>
Cc: "Yixun Lan" <dlan@kernel.org>, "Takashi Iwai" <tiwai@suse.com>,
	"Mark Brown" <broonie@kernel.org>,
	"Jaroslav Kysela" <perex@perex.cz>,
	"Liam Girdwood" <lgirdwood@gmail.com>,
	"Goko Mell" <goku.sonxin626@gmail.com>,
	"Jinmei Wei" <weijinmei@linux.spacemit.com>,
	"Kuninori Morimoto" <kuninori.morimoto.gx@renesas.com>,
	<linux-riscv@lists.infradead.org>, <spacemit@lists.linux.dev>,
	<linux-sound@vger.kernel.org>, <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] ASoC: spacemit: Remove redundant DAI field initialization
Date: Tue, 04 Aug 2026 02:59:36 -0700	[thread overview]
Message-ID: <DKG2L4V8Q2EU.1W5VODY60D6D7@linux.spacemit.com> (raw)
In-Reply-To: <CAABR9nFn0XW3CzAEncVkVKd65yBUEmquxjag6ybf_-NRf6mA8A@mail.gmail.com>


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> I traced the probe path and confirmed that snd_soc_dai_stream_valid()
> is called from soc_new_pcm().
> However, I still couldn't see where a nonzero channels_min alone leads
> to creating a capture substream
> without an RX DMA channel.
> To avoid confusion, I'm referring specifically to the DMA-based
> configuration, not PIO mode.
> Could you point me to the relevant call path?

More precisely, channels_min alone is not sufficient. The codec DAI must
also support capture (or be the dummy DAI for a dynamic link), and the link
must not be playback_only.

Under those conditions, the path is:

  soc_new_pcm()
    -> soc_get_playback_capture()
    -> soc_create_pcm(..., capture = 1)
    -> snd_pcm_new()
    -> snd_pcm_new_stream(CAPTURE, 1)
    -> snd_soc_pcm_component_new()
    -> dmaengine_pcm_new()

dmaengine_pcm_request_chan_of() tolerates a missing "rx" channel and leaves
pcm->chan[CAPTURE] NULL. Once the capture substream exists,
dmaengine_pcm_new() returns -EINVAL with
"Missing dma channel for stream: 1".
The conditional initialization prevents the CPU DAI from advertising that
direction for a tx-only node.

                                            - Troy

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  parent reply	other threads:[~2026-08-04  9:59 UTC|newest]

Thread overview: 12+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2026-08-04  4:30 [PATCH] ASoC: spacemit: Remove redundant DAI field initialization phucduc.bui
2026-08-04  4:30 ` phucduc.bui
2026-08-04  6:39 ` Troy Mitchell
2026-08-04  6:39   ` Troy Mitchell
2026-08-04  9:45   ` Bui Duc Phuc
2026-08-04  9:45     ` Bui Duc Phuc
2026-08-04  9:58     ` Troy Mitchell
2026-08-04  9:58       ` Troy Mitchell
2026-08-04  9:59     ` Troy Mitchell [this message]
2026-08-04  9:59       ` Troy Mitchell
2026-08-04 14:19       ` Bui Duc Phuc
2026-08-04 14:19         ` Bui Duc Phuc

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