Received-SPF: pass (google.com: domain of linux-kernel+bounces-162507-linux.lists.archive=gmail.com@vger.kernel.org designates 2604:1380:45d1:ec00::1 as permitted sender) client-ip=2604:1380:45d1:ec00::1;
Date: Mon, 29 Apr 2024 17:00:41 +0200
From: Johan Hovold <johan@kernel.org>
To: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
Cc: broonie@kernel.org, perex@perex.cz, tiwai@suse.com, lgirdwood@gmail.com,
	alsa-devel@alsa-project.org, linux-kernel@vger.kernel.org,
	Bjorn Andersson <quic_bjorande@quicinc.com>
Subject: Re: [PATCH v2 0/4] ASoC: qcom: display port changes
Message-ID: <Zi-2GVGZvWoIXO2c@hovoldconsulting.com>
References: <20240422134354.89291-1-srinivas.kandagatla@linaro.org>
 <ZieihZRKe7OtP-nV@hovoldconsulting.com>
 <92b02fd3-5eba-42a7-a166-21b14724b10c@linaro.org>
 <ZifMlc_rLV6_LhUy@hovoldconsulting.com>
 <fc3d849d-3a7e-439a-8d71-2b70ac75ae86@linaro.org>
Precedence: bulk
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <fc3d849d-3a7e-439a-8d71-2b70ac75ae86@linaro.org>

On Tue, Apr 23, 2024 at 04:59:56PM +0100, Srinivas Kandagatla wrote:
> On 23/04/2024 15:58, Johan Hovold wrote:

> >> It is absolutely possible to run all the streams in parallel from the
> >> Audio hardware and DSP point of view.
> >>
> >> One thing to note is, On Qualcomm DP IP, we can not read/write registers
> >> if the DP port is not connected, which means that we can not send data
> >> in such cases.
> >>
> >> This makes it challenging to work with sound-servers like pipewire or
> >> pulseaudio as they tend to send silence data at very early stages in the
> >> full system boot up, ignoring state of the Jack events.

> > This bit sounds like it can and should be worked around by the driver to
> > avoid hard-coding policy which would prevent use cases such as the ones
> > mentioned above.

> This is not simple as you say. We have to fit these into a proper DPCM.
> Either we have a dummy Backend connected for each of these pcm 
> sub-devices when DP port is not connected and then switch back to DP 
> when its connected.

I don't know how best to implement it, but we shouldn't necessarily let
that determine the user experience.

> Or somehow find a way to not let the pipewire talk to devices which are 
> not connected.

Yes, perhaps it requires a change in user space.

But it seems the kernel should be able to fake whatever probing user
space currently does to determine if the there is a DP jack (even when
there is nothing connected).

Johan