The Realtek PC Beep Hidden Register[1] is currently set by patch_realtek.c in two different places:

In alc_fill_eapd_coef(), it's set to the value 0x5757, corresponding to non-beep input on 1Ah and no 1Ah loopback to either headphones or speakers. (Although, curiously, the loopback amp is still enabled.) This write was added fairly recently by commit e3743f431143 ("ALSA: hda/realtek - Dell headphone has noise on unmute for ALC236") and is a safe default. However, it happens in the wrong place: alc_fill_eapd_coef() runs on module load and cold boot but not on S3 resume, meaning the register loses its value after suspend.

Conversely, in alc256_init(), the register is updated to unset bit 13 (disable speaker loopback) and set bit 5 (set non-beep input on 1Ah). Although this write does run on S3 resume, it's not quite enough to fix up the register's default value of 0x3717. What's missing is a set of bit 14 to disable headphone loopback. Without that, we end up with a feedback loop where the headphone jack is being driven by amplified samples of itself[2].

This change eliminates the update in alc256_init() and replaces it with the 0x5757 write from alc_fill_eapd_coef(). Kailang says that 0x5757 is supposed to be the codec's default value, so using it will make debugging easier for Realtek.

Affects the ALC255, ALC256, ALC257, ALC235, and ALC236 codecs.

[1] Newly documented in Documentation/sound/hd-audio/realtek-pc-beep.rst

[2] Setting the "Headphone Mic Boost" control from userspace changes this feedback loop and has been a widely-shared workaround for headphone noise on laptops like the Dell XPS 13 9350. This commit eliminates the feedback loop and makes the workaround unnecessary.

Fixes: e3743f431143 ("ALSA: hda/realtek - Dell headphone has noise on unmute for ALC236") Cc: stable@vger.kernel.org Signed-off-by: Thomas Hebb tommyhebb@gmail.com ---

Changes in v2: - Change fixed value from 0x4727 to 0x5757, which should behave identically, on advice from Kailang.

sound/pci/hda/patch_realtek.c | 15 +++++++++------ 1 file changed, 9 insertions(+), 6 deletions(-)

diff --git a/sound/pci/hda/patch_realtek.c b/sound/pci/hda/patch_realtek.c index 63e1a56f705b..9efb0a858c64 100644 --- a/sound/pci/hda/patch_realtek.c +++ b/sound/pci/hda/patch_realtek.c @@ -367,7 +367,9 @@ static void alc_fill_eapd_coef(struct hda_codec *codec) case 0x10ec0215: case 0x10ec0233: case 0x10ec0235: + case 0x10ec0236: case 0x10ec0255: + case 0x10ec0256: case 0x10ec0257: case 0x10ec0282: case 0x10ec0283: @@ -379,11 +381,6 @@ static void alc_fill_eapd_coef(struct hda_codec *codec) case 0x10ec0300: alc_update_coef_idx(codec, 0x10, 1<<9, 0); break; - case 0x10ec0236: - case 0x10ec0256: - alc_write_coef_idx(codec, 0x36, 0x5757); - alc_update_coef_idx(codec, 0x10, 1<<9, 0); - break; case 0x10ec0275: alc_update_coef_idx(codec, 0xe, 0, 1<<0); break; @@ -3269,7 +3266,13 @@ static void alc256_init(struct hda_codec *codec) alc_update_coefex_idx(codec, 0x57, 0x04, 0x0007, 0x4); /* Hight power */ alc_update_coefex_idx(codec, 0x53, 0x02, 0x8000, 1 << 15); /* Clear bit */ alc_update_coefex_idx(codec, 0x53, 0x02, 0x8000, 0 << 15); - alc_update_coef_idx(codec, 0x36, 1 << 13, 1 << 5); /* Switch pcbeep path to Line in path*/ + /* + * Expose headphone mic (or possibly Line In on some machines) instead + * of PC Beep on 1Ah, and disable 1Ah loopback for all outputs. See + * Documentation/sound/hd-audio/realtek-pc-beep.rst for details of + * this register. + */ + alc_write_coef_idx(codec, 0x36, 0x5757); }

static void alc256_shutup(struct hda_codec *codec)