[Bug 1905226] [NEW] intel-hda: stream reset bits are broken

[Jacob <1905226@bugs.launchpad.net>]

Public bug reported:

>From HD audio spec, section 3.3.35:

"Stream Reset (SRST): Writing a 1 causes the corresponding stream to be
reset. [...] After the stream hardware has completed sequencing into the
reset state, it will report a 1 in this bit. Software must read a 1 from
this bit to verify that the stream is in reset. Writing a 0 causes the
corresponding stream to exit reset. When the stream hardware is ready to
begin operation, it will report a 0 in this bit. Software must read a 0
from this bit before accessing any of the stream registers."

So to reset a stream I set the bit, but it never reads back as 1 so the
driver either times out or will hang forever waiting for it to become 1.
I looked into why this happens and found that as of the latest version
(8110fa1), in function intel_hda_set_st_ctl() of the
https://github.com/qemu/qemu/blob/master/hw/audio/intel-hda.c,

    if (st->ctl & 0x01) {
        /* reset */
        dprint(d, 1, "st #%d: reset\n", reg->stream);
        st->ctl = SD_STS_FIFO_READY << 24;
    }

This causes the bit to immediately become set to 0 even if I write a 1,
and clearly does not meet the spec. I checked behaviour of real hardware
and it works as expected, i.e. I see the bit will become 1 and 0 when I
write to it.

** Affects: qemu
     Importance: Undecided
         Status: New


** Tags: intel-hda

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https://bugs.launchpad.net/bugs/1905226

Title:
  intel-hda: stream reset bits are broken

Status in QEMU:
  New

Bug description:
  From HD audio spec, section 3.3.35:

  "Stream Reset (SRST): Writing a 1 causes the corresponding stream to
  be reset. [...] After the stream hardware has completed sequencing
  into the reset state, it will report a 1 in this bit. Software must
  read a 1 from this bit to verify that the stream is in reset. Writing
  a 0 causes the corresponding stream to exit reset. When the stream
  hardware is ready to begin operation, it will report a 0 in this bit.
  Software must read a 0 from this bit before accessing any of the
  stream registers."

  So to reset a stream I set the bit, but it never reads back as 1 so
  the driver either times out or will hang forever waiting for it to
  become 1. I looked into why this happens and found that as of the
  latest version (8110fa1), in function intel_hda_set_st_ctl() of the
  https://github.com/qemu/qemu/blob/master/hw/audio/intel-hda.c,

      if (st->ctl & 0x01) {
          /* reset */
          dprint(d, 1, "st #%d: reset\n", reg->stream);
          st->ctl = SD_STS_FIFO_READY << 24;
      }

  This causes the bit to immediately become set to 0 even if I write a
  1, and clearly does not meet the spec. I checked behaviour of real
  hardware and it works as expected, i.e. I see the bit will become 1
  and 0 when I write to it.

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