Re: [PATCH 3/6] ASoC: codecs: wcd938x: Check for enumeration before using TX device

Pierre-Louis Bossart
2023-04-20T17:15:29Z

On 4/20/23 05:16, Krzysztof Kozlowski wrote:
> Qualcomm WCD938x Soundwire codecs come as two Soundwire devices - TX
> and RX - on two Soundwire buses. In DTS they are represented as three
> device nodes: Soundwire TX, Soundwire RX and the platform codec node
> (binding to this driver).
>
> Probing (and Soundwire enumeration) of all devices can happen in any
> order, but only the Soundwire TX WCD938x device is used for accessing
> actual WCD938x registers. It is possible that component bind() in the
> platform driver will be called too early, before the Soundwire TX device
> is fully enumerated. This might work or might not, but we cannot handle
> it correctly from the codec driver. It's job for Soundwire master to
> bring up devices in correct order.

That last sentence isn't aligned with the way enumeration works in
general for SoundWire.

The Manager starts the clock, usually after a bus reset, and waits for
Peripherals to signal their presence with Device0 Attached.

If multiple Peripherals are attached as Device0, the enumeration will
resolve conflicts at the hardware level, and the Manager *cannot*
control the order of enumeration; the order is defined by the values in
the devID registers, whichever Peripheral has the highest value in the
DevID registers wins the enumeration, and others have to back-off and be
enumerated later.

Probing and enumeration are also different concepts. The SoundWire
design allows for drivers to be probed even in the absence of any active
hardware. This was added on purpose so that the driver could e.g.
program a GPIO or talk to a power-management chip to allow SoundWire
devices to start interacting with the bus.

see also suggestion below...

> Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
>
> ---
>
> Cc: Patrick Lai <quic_plai@quicinc.com>
> ---
> sound/soc/codecs/wcd938x.c | 11 +++++++++++
> 1 file changed, 11 insertions(+)
>
> diff --git a/sound/soc/codecs/wcd938x.c b/sound/soc/codecs/wcd938x.c
> index 212667a7249c..e8e07e120fa1 100644
> --- a/sound/soc/codecs/wcd938x.c
> +++ b/sound/soc/codecs/wcd938x.c
> @@ -77,6 +77,8 @@
> #define WCD938X_MBHC_MOISTURE_RREF R_24_KOHM
> #define WCD_MBHC_HS_V_MAX 1600
>
> +#define WCD938X_ENUM_TIMEOUT_MS 500
> +
> #define WCD938X_EAR_PA_GAIN_TLV(xname, reg, shift, max, invert, tlv_array) \
> { .iface = SNDRV_CTL_ELEM_IFACE_MIXER, .name = xname, \
> .access = SNDRV_CTL_ELEM_ACCESS_TLV_READ |\
> @@ -4425,6 +4427,15 @@ static int wcd938x_bind(struct device *dev)
> wcd938x->sdw_priv[AIF1_PB]->slave_irq = wcd938x->virq;
> wcd938x->sdw_priv[AIF1_CAP]->slave_irq = wcd938x->virq;
>
> + /*
> + * Before any TX slave regmap usage, be sure the TX slave is actually
> + * enumerated.
> + */

...

the alternative is to move regmap to be cache-only in the probe and
remove the cache-only property when the device is enumerated.

That's a trick that's used for all resume cases in codecs in Intel
platforms, and we need to extend it for the startup cases as well.

> + ret = wait_for_completion_timeout(&wcd938x->tx_sdw_dev->enumeration_complete,
> + msecs_to_jiffies(WCD938X_ENUM_TIMEOUT_MS));
> + if (!ret)
> + dev_warn(dev, "Enumeration timeout in bind, possible failures in accessing registers\n");
> +
> ret = wcd938x_set_micbias_data(wcd938x);
> if (ret < 0) {
> dev_err(dev, "%s: bad micbias pdata\n", __func__);