ASoC: wm8962: don't clear a SYSCLK_ENA that DAPM owns in configure_bclk (fixes silent audio on Surface RT / Surface 2) - #142
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wm8962_configure_bclk() provisionally sets SYSCLK_ENA so that the read-only DSPCLK_DIV field becomes valid, then clears it again whenever the bias level is below SND_SOC_BIAS_ON. It never checks whether the bit was already set. It can be: the "SYSCLK" DAPM supply widget owns that bit, and wm8962_mic_detect() force-enables the pin. On boards that call it (the Tegra machine driver, i.e. Microsoft Surface RT and Surface 2) DAPM sets SYSCLK_ENA once at card init and, because the widget then never changes power state, never writes it again. The first stream's transition to SND_SOC_BIAS_PREPARE runs configure_bclk(), which clears the bit behind DAPM's back. From then on every stream plays with SYSCLK off: the DACs do not run, CP_ENA refuses to latch, hp_event() reports "DC servo timed out", and the codec is silent although every register DAPM believes in looks right. Remember whether SYSCLK_ENA was set on entry and only undo our own provisional enable. Verified on a Microsoft Surface 2 (Tegra 4, WM8962 rev F): with the bit forced on over I2C during a stream the DC servo completes in ~56 ms and audio is heard; with this patch applied the DC servo completes on every stream and there is no more "DC servo timed out". Fixes: 75704ec ("ASoC: wm8962: Enable SYSCLK provisonally before fetching generated DSPCLK_DIV") Cc: stable@vger.kernel.org Co-authored-by: Claude Fable 5.1 <noreply@anthropic.com> Signed-off-by: Maxime Douailin <maxime.douailin@gmail.com>
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Fixes #141 and, I expect, the silence reported in #140 too.
The bug
wm8962_configure_bclk()provisionally setsSYSCLK_ENAto read the read-onlyDSPCLK_DIV, then clears it unconditionally when the bias level is belowSND_SOC_BIAS_ON. But that bit is owned by theSYSCLKDAPM supply widget, andwm8962_mic_detect()force-enables that pin. The Tegra machine driver callswm8962_mic_detect(), so on Surface RT / Surface 2 DAPM writesSYSCLK_ENA = 1once at card init and never again (the widget never changes power state). The first stream'sBIAS_PREPARErunsconfigure_bclk(), which clears the bit behind DAPM's back. Every stream then plays with SYSCLK off: DACs idle,CP_ENAwill not latch,hp_event()logsDC servo timed out, total silence while every DAPM-visible register looks right.Only boards calling
wm8962_mic_detect()are affected, which is exactly the two Surfaces.Verification
Microsoft Surface 2 (T114, WM8962 rev F), libre-tegra
stable7.0.1 + this patch: DC servo completes on every stream,SYSCLK_ENA/CP_ENAread 1 over I2C during playback, zero wm8962 errors in dmesg, speakers audible. Before the patch, forcing bit 5 of R8 over I2C during a stream produced sound immediately; that is how it was found (regmap cache vs. raw I2C register diff).Notes
Fixes: 75704ecfbb41andCc: stable, is going to linux-sound / alsa-devel: https://gist.github.com/zefr0g/97ff52172502ccde6a23dfd6c71608fcti,palmas-override-powerhold, microSD slot, audio pinmux + codec supplies) targetcodeberg.org/libre-tegra/linuxstable, which this repo'smasterdoes not carry. They are on branch https://github.com/zefr0g/linux/tree/surface2-fixes (top 4 commits) for whoever can land them there.🤖 Generated with Claude Code