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

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Date:   Mon, 11 Feb 2019 22:06:30 +0100
From:   Peter Seiderer <ps.report@....net>
To:     linux-kernel@...r.kernel.org
Cc:     Liam Girdwood <lgirdwood@...il.com>,
        Mark Brown <broonie@...nel.org>,
        Jaroslav Kysela <perex@...ex.cz>,
        Takashi Iwai <tiwai@...e.com>, b-ak <anur.bhargav@...il.com>,
        Kuninori Morimoto <kuninori.morimoto.gx@...esas.com>,
        alsa-devel@...a-project.org
Subject: [RFC v2] tlv320aic32x4: delay i2c access by 1 ms after hardware reset

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@....net>
---
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)) {
 		ndelay(10);
 		gpio_set_value(aic32x4->rstn_gpio, 1);
+		mdelay(1);
 	}
 
 	snd_soc_component_write(component, AIC32X4_RESET, 0x01);
-- 
2.20.1