[RFC v2] tlv320aic32x4: delay i2c access by 1 ms after hardware reset

From: Peter Seiderer
Date: Mon Feb 11 2019 - 16:07:21 EST

As stated in 'TLV320AIC3254 Application Reference Guide' ([1]):

3.2 Device Startup Lockout Times
After the TLV320AIC3254 initializes through hardware reset at power-up
or software reset, the internal registers initialize to default values.
This initialization takes place within 1ms after pulling the RESET
signal high. During this initialization phase, no register-read or
register-write operation should be performed on ADC or DAC coefficient
buffers. Also, no block within the codec should be powered up during
the initialization phase.

[1] http://www.ti.com/lit/an/slaa408a/slaa408a.pdf

Signed-off-by: Peter Seiderer <ps.report@xxxxxxx>
Changes v1 -> v2:
- call mdelay only in case the reset gpio was toggled (suggested
by Mark Brown)

Note: This came up after the electronic departement took a deeper look at
the i2c-bus/vcc/reset pins with a logic analyzer and the documentation
because of a vcc/reset timing problem (now fixed on custom board).
Not 100% sure if the 1 ms is needed (as restricted to ADC/DAC coefficent
and codec block power up).
sound/soc/codecs/tlv320aic32x4.c | 1 +
1 file changed, 1 insertion(+)

diff --git a/sound/soc/codecs/tlv320aic32x4.c b/sound/soc/codecs/tlv320aic32x4.c
index e1bfba62fc08..96f1526cb258 100644
--- a/sound/soc/codecs/tlv320aic32x4.c
+++ b/sound/soc/codecs/tlv320aic32x4.c
@@ -970,6 +970,7 @@ static int aic32x4_component_probe(struct snd_soc_component *component)
if (gpio_is_valid(aic32x4->rstn_gpio)) {
gpio_set_value(aic32x4->rstn_gpio, 1);
+ mdelay(1);

snd_soc_component_write(component, AIC32X4_RESET, 0x01);