Problem (interrupt storm) with snd_ich

From: Daan Vreeken [PA4DAN] (Danovitsch_at_vitsch.net)
Date: 12/04/04

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    To: FreeBSD-Hackers@FreeBSD.org
Date: Sat, 4 Dec 2004 14:23:36 +0100

    Hi All,

    I'm having a problem with the snd_ich driver. Directly after loading the
    snd_ich module pcm0 is detected correctly, but "vmstat -i" shows about 40000
    interrupts every second caused by pcm0.
    The problem shows up with both custom kernels and GENERIC, with or without
    snd_ich compiled into the kernel.

    After adding a printf() to the ich_intr() routine it showed that all
    interrupts have 0x400 (ICH_GLOB_STA_PRES) set. The ich_intr() has a comment
    about clearing this interrupt in the following lines :

     /* Clear resume interrupt(s) - nothing doing with them */
     ich_wr(sc, ICH_REG_GLOB_STA, gs, 4);

    Although this code should clear the interrupt, this doesn't seem to work on my
    laptop somehow.
    In ich_init() ICH_GLOB_CTL_PRES gets set in the ICH_REG_GLOB_CNT register. If
    I remove this bit in ich_init(), the interrupt problem goes away and pcm0
    works as expected. I have changed the following line in ich_init() :

    Original line :
     ich_wr(sc, ICH_REG_GLOB_CNT, ICH_GLOB_CTL_COLD | ICH_GLOB_CTL_PRES, 4);
    New line :
     ich_wr(sc, ICH_REG_GLOB_CNT, ICH_GLOB_CTL_COLD, 4);

    I'm not an ICH expert, so I don't know if I have just disabled a
    suspend/resume feature that is really needed or not, but it does solve my
    problem. I would like to know if anyone else has seen this problem before,
    and if there is a better solution to it.

    The relevant part of "pciconf -lv" :
    pcm0@pci0:2:7: class=0x040100 card=0x17631043 chip=0x70121039 rev=0xa0
    hdr=0x00
        vendor = 'Silicon Integrated Systems (SiS)'
        device = 'SiS7012 PCI Audio Accelerator'
        class = multimedia
        subclass = audio

    Feel free to ask for more information. I'm willing to test patches and give
    feedback.

    Thanks,
    Daan
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