summaryrefslogtreecommitdiffstats
path: root/sound/soc/tegra
diff options
context:
space:
mode:
authorOskar Schirmer <oskar@scara.com>2017-08-25 21:36:56 +0000
committerMark Brown <broonie@kernel.org>2017-08-29 20:50:24 +0100
commit1bb7cb68feb73a8106546cbd3379590297b0a950 (patch)
tree78a7319f991dc79b9a8e94f73000ee862309cb3e /sound/soc/tegra
parent5771a8c08880cdca3bfb4a3fc6d309d6bba20877 (diff)
downloadlinux-1bb7cb68feb73a8106546cbd3379590297b0a950.tar.bz2
ASoC: tas2552: Fix fraction overflow in PLL calculation
Setting the PLL involves the calculation of a fixed point ratio with 4 decimal digits fraction, referred to as "J.D". The fraction "D" is stored separately from the integer part "J" and is limited to 0..9999. The current algorithm uses integer registers to calculate the fraction part, but failed to compensate for rounding errors, resulting in values larger than 9999 for the fraction part occasionally, e.g. for 44.1kHz audio rate and pll_clkin = 3763400 it would set J to 11 and D to 10002, which will at best result in wrong pitch. The critical part is the "pll_clkin / 10000", which would be ok with real numbers, but using integer arithmetic the rounding decreases the divisor, thus increasing the final quotient. The issue is solved by linear interpolation over the reciprocal function between the two adjacent points with integer divisor, i.e. pll_clkin / 10000 and pll_clkin / 10000 + 1, and doing all rounding to the lower result. As a side effect to the bug fix, the approximation to the desired frequency is much better, for the above mentioned example we get 11.9993, while the true ratio is 11.9993623. Signed-off-by: Oskar Schirmer <oskar@scara.com> Signed-off-by: Mark Brown <broonie@kernel.org>
Diffstat (limited to 'sound/soc/tegra')
0 files changed, 0 insertions, 0 deletions