| lists.openwall.net | lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC | |
|
Open Source and information security mailing list archives
| ||
|
Message-ID: <e3bbd92e-57bc-4848-b7e4-1aa10202e9fa@oss.qualcomm.com>
Date: Thu, 23 Oct 2025 10:25:08 +0100
From: Srinivas Kandagatla <srinivas.kandagatla@....qualcomm.com>
To: Alexey Klimov <alexey.klimov@...aro.org>, broonie@...nel.org
Cc: perex@...ex.cz, tiwai@...e.com, srini@...nel.org,
linux-sound@...r.kernel.org, m.facchin@...uino.cc,
linux-kernel@...r.kernel.org, linux-arm-msm@...r.kernel.org
Subject: Re: [PATCH 6/9] ASoC: qcom: q6asm-dai: schedule all available frames
to avoid dsp under-runs
On 10/20/25 5:06 PM, Alexey Klimov wrote:
> On Wed Oct 15, 2025 at 2:17 PM BST, Srinivas Kandagatla wrote:
>> With the existing code, we are only setting up one period at a time, in a
>> ping-pong buffer style. This triggers lot of underruns in the dsp
>> leading to jitter noise during audio playback.
>>
>> Fix this by scheduling all available periods, this will ensure that the dsp
>> has enough buffer feed and ultimatley fixing the underruns and audio distortion.
>>
>> Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@....qualcomm.com>
>> ---
>> sound/soc/qcom/qdsp6/q6asm-dai.c | 34 +++++++++++++++++++++++++-------
>
> [..]
>
>> +static int q6asm_dai_ack(struct snd_soc_component *component, struct snd_pcm_substream *substream)
>> +{
>> + struct snd_pcm_runtime *runtime = substream->runtime;
>> + struct q6asm_dai_rtd *prtd = runtime->private_data;
>> + int i, ret = 0, avail_periods;
>> +
>> + if (substream->stream == SNDRV_PCM_STREAM_PLAYBACK && prtd->state == Q6ASM_STREAM_RUNNING) {
>> + avail_periods = (runtime->control->appl_ptr - prtd->queue_ptr)/runtime->period_size;
>> + for (i = 0; i < avail_periods; i++) {
>> + ret = q6asm_write_async(prtd->audio_client, prtd->stream_id,
>> + prtd->pcm_count, 0, 0, 0);
>> +
>> + if (ret < 0) {
>> + dev_err(component->dev, "Error queuing playback buffer %d\n", ret);
>> + return ret;
>> + }
>> + prtd->queue_ptr += runtime->period_size;
>> + }
>> + }
>> +
>> + return ret;
>> +}
We have exactly same logic in q6apm-dai.c I will keep this as it is for
this patch series, we can always improve this over time. Patches welcome.>
> So when I compiled this on a common arm64 desktop machine with defconfig,
> nothing fancy, with gcc, this loop and function really does compile with
> udiv instruction.
>
> avail_periods = (runtime->control->appl_ptr - prtd->queue_ptr)/runtime->period_size;
> 350: f9001bf7 str x23, [sp, #48]
> 354: f94086a0 ldr x0, [x21, #264]
> 358: f9408262 ldr x2, [x19, #256]
> 35c: f9400000 ldr x0, [x0]
> 360: f9403ea1 ldr x1, [x21, #120]
> 364: cb020000 sub x0, x0, x2
> 368: 9ac10800 udiv x0, x0, x1 <--- here
> 36c: 2a0003f7 mov w23, w0
>
> What do you think about rewriting this loop without division and
> without using additional iterator? I don't think this is a hot path
> but anyway.
>
> The first iteration that I came up with is (1):
>
>
> diff --git a/sound/soc/qcom/qdsp6/q6asm-dai.c b/sound/soc/qcom/qdsp6/q6asm-dai.c
> index 97256313c01a..d01f805947b8 100644
> --- a/sound/soc/qcom/qdsp6/q6asm-dai.c
> +++ b/sound/soc/qcom/qdsp6/q6asm-dai.c
> @@ -310,6 +310,23 @@ static int q6asm_dai_ack(struct snd_soc_component *component, struct snd_pcm_sub
> int ret = 0;
>
> if (substream->stream == SNDRV_PCM_STREAM_PLAYBACK && prtd->state == Q6ASM_STREAM_RUNNING) {
> + if (prtd->queue_ptr < runtime->control->appl_ptr) {
This is not going to work, as we need alteast 1 period of data.> +
> + do {
> + ret = q6asm_write_async(prtd->audio_client, prtd->stream_id,
> + prtd->pcm_count, 0, 0, 0);
> +
> + if (ret < 0) {
> + dev_err(component->dev, "Error queuing playback buffer %d\n", ret);
> + return ret;
> + }
> +
> + prtd->queue_ptr += runtime->period_size;
This queue_ptr can go over appl_ptr.. can impact sound quality as we
will be queuing something that is not in the data yet.
--srini> +
> + } while (prtd->queue_ptr < runtime->control->appl_ptr);
> +
> + }
>
> No division and no calculation of iterator and avail_periods.
>
> Rewriting it further (2):
>
> diff --git a/sound/soc/qcom/qdsp6/q6asm-dai.c b/sound/soc/qcom/qdsp6/q6asm-dai.c
> index 97256313c01a..317f06d07a09 100644
> --- a/sound/soc/qcom/qdsp6/q6asm-dai.c
> +++ b/sound/soc/qcom/qdsp6/q6asm-dai.c
> @@ -307,9 +307,26 @@ static int q6asm_dai_ack(struct snd_soc_component *component, struct snd_pcm_sub
> {
> struct snd_pcm_runtime *runtime = substream->runtime;
> struct q6asm_dai_rtd *prtd = runtime->private_data;
> - int i, ret = 0, avail_periods;
> + int ret = 0, diff;
>
> if (substream->stream == SNDRV_PCM_STREAM_PLAYBACK && prtd->state == Q6ASM_STREAM_RUNNING) {
> + diff = (runtime->control->appl_ptr - prtd->queue_ptr);
> +
> + while (diff >= runtime->period_size) {
> + ret = q6asm_write_async(prtd->audio_client, prtd->stream_id,
> + prtd->pcm_count, 0, 0, 0);
> +
> + if (ret < 0) {
> + dev_err(component->dev, "Error queuing playback buffer %d\n", ret);
> + return ret;
> + }
> +
> + prtd->queue_ptr += runtime->period_size;
> + diff -= runtime->period_size;
> + };
> +
> +
>
> Surprisingly, in (1) the size of resulting object file is smaller than in (2):
>
> With original patch: 110008 Oct 20 15:26 sound/soc/qcom/qdsp6/q6asm-dai.o
> with (1): 109776 Oct 20 16:53 sound/soc/qcom/qdsp6/q6asm-dai.o
> with (2): 109896 Oct 20 16:52 sound/soc/qcom/qdsp6/q6asm-dai.o
>
> I think the readability won't be damaged as a result of the rewriting
> and the code seems to be smaller.
> Obviusly, this needs to be verified for some corner cases and etc.
> I'd go with (1) but it is up to you. I tested (1) and it seems to work.
>
> Best regards,
> Alexey
>
>
>
>
>
Powered by blists - more mailing lists