Reading this extract from the HDA PRM in conjunction with
azx_setup_controller() (note my ***...*** highlights) might suggest a
problem with "...the hardware may still have pre-fetched descriptors
that will not be flushed when the stream is restarted...":
4.6.6
After the RUN bit has been set, the buffer described by the BDL should not be
changed by the
software. The hardware may pre-fetch and/or cache an arbitrary number of BDL
Entries from the
list, so there is no way to ensure when or if any changes to the BDL list would
be visible to the
hardware.
*** Even when the RUN bit has been cleared to pause the stream after it has
been running,
the hardware may still have pre-fetched descriptors that will not be flushed
when the stream is
restarted. Therefore, the software should only modify the BDL before the RUN
bit has been set for
the first time after a Stream Reset. ***
/* make sure the run bit is zero for SD */
azx_sd_writeb(azx_dev, SD_CTL, azx_sd_readb(azx_dev, SD_CTL) &
~SD_CTL_DMA_START);
/* reset stream */
azx_sd_writeb(azx_dev, SD_CTL, azx_sd_readb(azx_dev, SD_CTL) |
SD_CTL_STREAM_RESET);
udelay(3);
timeout = 300;
while (!((val = azx_sd_readb(azx_dev, SD_CTL)) & SD_CTL_STREAM_RESET) &&
--timeout)
;
val &= ~SD_CTL_STREAM_RESET;
azx_sd_writeb(azx_dev, SD_CTL, val);
udelay(3);
timeout = 300;
/* waiting for hardware to report that the stream is out of reset */
while (((val = azx_sd_readb(azx_dev, SD_CTL)) & SD_CTL_STREAM_RESET) &&
--timeout);
--
snd-hda-intel: distorted sound after resume, until the module is reloaded
https://bugs.launchpad.net/bugs/100114
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