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  1. Dec 02, 2013
    • Oskar Schirmer's avatar
      ASoC: fsl: imx-pcm-fiq: remove bogus period delta calculation · d6437c14
      Oskar Schirmer authored 
      

Originally snd_hrtimer_callback() used iprtd->period_time for
some jiffies based estimation to determine the right moment
to call snd_pcm_period_elapsed(). As timer drifts may well be a
problem, this was changed in commit b4e82b5b to be based
on buffer transmission progress, using iprtd->offset and
runtime->buffer_size to calculate the amount of data since last
period had elapsed.

Unfortunately, iprtd->offset counts in bytes, while
runtime->buffer_size counts frames, so adding these to find some
delta is like comparing apples and oranges, and eventually results
in negative delta values every now and then. This is no big harm,
because it simply causes snd_pcm_period_elapsed() being called
more often than necessary, as negative delta is taken for a
large unsigned value by implicit conversion rule.
Nonetheless, the calculation is broken, so one would replace
the runtime->buffer_size by its equivalent in bytes.

But then, there are chances snd_pcm_period_elapsed() is called
late, because calculating the moment for the elapsed period
into delta is based against the iprtd->last_offset, which is not
necessarily the first byte of the period in question, but some
random byte which the FIQ handler left us with in r8/r9 by
accident. Again, negative impact is low, as there are plenty of
periods already prefilled with data, and snd_pcm_period_elapsed()
will probably be called latest when the following period is
reached. However, the calculation is conceptually broken, and we
are best off removing the clever stuff altogether.

snd_pcm_period_elapsed() is now simply called once everytime
snd_hrtimer_callback() is run, which may not be most accurate,
but at least this way we are quite sure we dont miss an end of
period. There is not much extra effort wasted by superfluous
calls to snd_pcm_period_elapsed(), as the timer frequency
closely matches the period size anyway.

Signed-off-by: default avatarOskar Schirmer <oskar@scara.com>
Signed-off-by: default avatarMark Brown <broonie@linaro.org>
      d6437c14
  3. Nov 14, 2013
    • Oskar Schirmer's avatar
      ASoC: fsl: imx-pcm-fiq: omit fiq counter to avoid harm in unbalanced situations · fc7dc61d
      Oskar Schirmer authored 
      

Unbalanced calls to snd_imx_pcm_trigger() may result in endless
FIQ activity and thus provoke eternal sound. While on the first glance,
the switch statement looks pretty symmetric, the SUSPEND/RESUME
pair is not: the suspend case comes along snd_pcm_suspend_all(),
which for fsl/imx-pcm-fiq is called only at snd_soc_suspend(),
but the resume case originates straight from the SNDRV_PCM_IOCTL_RESUME.
This way userland may provoke an unbalanced resume, which might cause
the fiq_enable counter to increase and never return to zero again,
so eventually imx_pcm_fiq is never disabled.

Simply removing the fiq_enable will solve the problem, as long as
one never goes play and capture game simultaneously, but beware
trying both at once, the early TRIGGER_STOP will cut off the other
activity prematurely. So now playing and capturing is scrutinized
separately, instead of by counting.

Signed-off-by: default avatarOskar Schirmer <oskar@scara.com>
Signed-off-by: default avatarMark Brown <broonie@linaro.org>
Cc: stable@vger.kernel.org
      fc7dc61d
  5. Nov 04, 2013
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