Re: snd_pcm_set_params faild on set_buffer_time_near and set_period_time_near

[Martin Geier <martin.geier@streamunlimited.com>]

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Thanks for help,

in attachment is patch with suggest change.
Is the patch acceptable?

Martin

On 23.07.2015 10:11, Takashi Iwai wrote:
> On Tue, 21 Jul 2015 10:52:01 +0200,
> Martin Geier wrote:
>> Hallo,
>>
>> I tried to configure alsa device with snd_pcm_set_params function,
>> requested
>> parameters was:
>> channel 2, rate: 22050, soft_resample: 1, latency: 50000
>>
>> Function snd_pcm_hw_params_set_buffer_time_near and
>> snd_pcm_hw_param_set_near
>> is called with:
>> min: 50000, max: 50000, mindir: 0, maxdir: -1
>>
>> and input params was:
>>
>> ACCESS:  RW_INTERLEAVED
>> FORMAT:  S16_LE
>> SUBFORMAT:  STD
>> SAMPLE_BITS: 16
>> FRAME_BITS: 32
>> CHANNELS: 2
>> RATE: 22050
>> PERIOD_TIME: (362 743039)
>> PERIOD_SIZE: [8 16384]
>> PERIOD_BYTES: [32 65536]
>> PERIODS: [2 19]
>> BUFFER_TIME: (725 1486078)
>> BUFFER_SIZE: [16 32768]
>> BUFFER_BYTES: [64 131072]
>> TICK_TIME: ALL
>>
>> unfortunately, this function fails, on function snd_pcm_hw_param_set_first:
>>
>> ALSA ERROR hw_params: set_near (BUFFER_TIME)
>>              value = 50000 : Invalid argument
>> ACCESS:  RW_INTERLEAVED
>> FORMAT:  S16_LE
>> SUBFORMAT:  STD
>> SAMPLE_BITS: 16
>> FRAME_BITS: 32
>> CHANNELS: 2
>> RATE: 22050
>> PERIOD_TIME: (4580 5533)
>> PERIOD_SIZE: NONE
>> PERIOD_BYTES: [404 488]
>> PERIODS: 10
>> BUFFER_TIME: (50022 50023)
>> BUFFER_SIZE: 1103
>> BUFFER_BYTES: 4412
>> TICK_TIME: ALL
>>
>> This shouldn't be problem because in snd_pcm_set_params is
>> snd_pcm_hw_params_set_period_time_near called.
>> This function should be called with same params as
>> snd_pcm_hw_params_set_buffer_time_near
>> but the input params are:
>>
>> snd_pcm_hw_param_set_near: min: 12500, max: 12500, mindir: 0, maxdir: -1
>> hw_params: snd_pcm_hw_param_set_near (PERIOD_TIME)
>> ACCESS:  RW_INTERLEAVED
>> FORMAT:  S16_LE
>> SUBFORMAT:  STD
>> SAMPLE_BITS: 16
>> FRAME_BITS: 32
>> CHANNELS: 2
>> RATE: 22050
>> PERIOD_TIME: (4580 5533)
>> PERIOD_SIZE: NONE
>> PERIOD_BYTES: [404 488]
>> PERIODS: 10
>> BUFFER_TIME: (50022 50023)
>> BUFFER_SIZE: 1103
>> BUFFER_BYTES: 4412
>> TICK_TIME: ALL
>>
>> because in snd_pcm_hw_param_set_near is
>>
>> if (last)
>>       err = snd_pcm_hw_param_set_last(pcm, params, var, val, dir);
>> else
>>       err = snd_pcm_hw_param_set_first(pcm, params, var, val, dir);
>> if (err < 0)
>>       dump_hw_params(params, "set_near", var, *val, err);
>> return err;
>>
>> and in error part is only debug output and not restore original parameters.
>>
>> Environment:
>> alsa-lib 1.0.27.1
>> TI AM335x soc
>>
>> Simple fix is attached, but I am not sure if it is correct.
> Thanks for analysis and patch.  It's however rather a bug in
> snd_pcm_set_params().  There is no guarantee to keep the old value in
> snd_pcm_set_*(), thus the caller needs to take care of it instead.
>
>
> Takashi
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[-- Attachment #2: 0001-PATCH-restore-hw-params-on-set-rate-failed.patch --]
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>From 2d4e94d974678bbd4826b33c59c275d1f34edc20 Mon Sep 17 00:00:00 2001
From: Martin Geier <martin.geier@streamunlimited.com>
Date: Fri, 24 Jul 2015 09:30:57 +0200
Subject: [PATCH] restore hw params on set rate failed

---
 pcm.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/src/pcm/pcm.c b/src/pcm/pcm.c
index ca4d416..b6de73e 100644
--- a/src/pcm/pcm.c
+++ b/src/pcm/pcm.c
@@ -7883,7 +7883,7 @@ int snd_pcm_set_params(snd_pcm_t *pcm,
                        int soft_resample,
                        unsigned int latency)
 {
-        snd_pcm_hw_params_t *params;
+        snd_pcm_hw_params_t *params, pparams;
         snd_pcm_sw_params_t *swparams;
         const char *s = snd_pcm_stream_name(snd_pcm_stream(pcm));
         snd_pcm_uframes_t buffer_size, period_size;
@@ -7936,9 +7936,11 @@ int snd_pcm_set_params(snd_pcm_t *pcm,
 		return -EINVAL;
 	}
 	/* set the buffer time */
+	pparams = *params;
 	err = INTERNAL(snd_pcm_hw_params_set_buffer_time_near)(pcm, params, &latency, NULL);
 	if (err < 0) {
 	        /* error path -> set period size as first */
+			*params = pparams;
         	/* set the period time */
         	period_time = latency / 4;
         	err = INTERNAL(snd_pcm_hw_params_set_period_time_near)(pcm, params, &period_time, NULL);
-- 
1.9.1


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