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    SubjectLoud screech after reboot of 2.2.18-pre22

    I have a Sony VAIO Z505JE with ymfpci sound and built-in microphone
    and speaker. Everything worked fine with 2.2.17 plus ymfpci patch,
    but the 2.2.18-pre22 produces a loud screech starting as sound
    initializes and ending when startup scrips load mixer settings.
    This happens because of audio loop between microphone and speakers.

    I found that the culprit is the change to values of array
    mixer_defaults[] in ac97_codec.c, that happened in 2.2.18-pre.

    Currently I run the following patch:

    --- linux-2.2.18-pre22/drivers/sound/ac97_codec.c Sat Nov 18 19:04:34 2000
    +++ linux-2.2.18-pre22-p3/drivers/sound/ac97_codec.c Sun Nov 19 15:37:44 2000
    @@ -131,7 +131,7 @@
    {SOUND_MIXER_PCM, 0x4343},
    {SOUND_MIXER_SPEAKER, 0x4343},
    {SOUND_MIXER_LINE, 0x4343},
    - {SOUND_MIXER_MIC, 0x4343},
    + {SOUND_MIXER_MIC, 0x1111}, /* P3 - audio loop */
    {SOUND_MIXER_CD, 0x4343},
    {SOUND_MIXER_ALTPCM, 0x4343},
    {SOUND_MIXER_IGAIN, 0x4343},
    I wonder if there is a better way?

    In the interests of full disclosure let me mention that YMFxxx do have
    internal loopbacks that may produce the same effect and that I checked
    to the best of my ability that those loopbacks are muted. Therefore
    I conclude that the loopback happens inside the AC97 (if such a thing
    is possible).

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