linux-kernel - Re: [PATCH 1/2] usb: typec: tps6598x: add reset gpio support

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Message-ID: <f3184a12-fd2d-1812-e196-c3e59e841632@wolfvision.net>
Date:   Fri, 15 Sep 2023 12:07:08 +0200
From:   Javier Carrasco <javier.carrasco@...fvision.net>
To:     Bryan O'Donoghue <bryan.odonoghue@...aro.org>,
        Heikki Krogerus <heikki.krogerus@...ux.intel.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Conor Dooley <conor+dt@...nel.org>
Cc:     linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org,
        devicetree@...r.kernel.org
Subject: Re: [PATCH 1/2] usb: typec: tps6598x: add reset gpio support

Hello Bryan,

On 15.09.23 11:52, Bryan O'Donoghue wrote:
> On 15/09/2023 07:50, Javier Carrasco wrote:
>> The TPS6598x PD controller provides an active-high hardware reset input
>> that reinitializes all device settings. If it is not grounded by
>> design, the driver must be able to de-assert it in order to initialize
>> the device.
>>
>> The PD controller is not ready for registration right after the reset
>> de-assertion and a delay must be introduced in that case. According to
>> TI, the delay can reach up to 1000 ms [1], which is in line with the
>> experimental results obtained with a TPS65987D.
>>
>> Add a GPIO descriptor for the reset signal and basic reset management
>> for initialization and suspend/resume.
>>
>> [1]
>> https://e2e.ti.com/support/power-management-group/power-management/
>> f/power-management-forum/1269856/tps65987d-tps65987d-reset-de-assert-
>> to-normal-operation/4809389#4809389
>>
>> Signed-off-by: Javier Carrasco <javier.carrasco@...fvision.net>
>> ---
>>   drivers/usb/typec/tipd/core.c | 21 ++++++++++++++++++++-
>>   1 file changed, 20 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/usb/typec/tipd/core.c
>> b/drivers/usb/typec/tipd/core.c
>> index 37b56ce75f39..550f5913e985 100644
>> --- a/drivers/usb/typec/tipd/core.c
>> +++ b/drivers/usb/typec/tipd/core.c
>> @@ -8,6 +8,7 @@
>>     #include <linux/i2c.h>
>>   #include <linux/acpi.h>
>> +#include <linux/gpio/consumer.h>
>>   #include <linux/module.h>
>>   #include <linux/of.h>
>>   #include <linux/power_supply.h>
>> @@ -43,6 +44,9 @@
>>   /* TPS_REG_SYSTEM_CONF bits */
>>   #define TPS_SYSCONF_PORTINFO(c)        ((c) & 7)
>>   +/* reset de-assertion to ready for operation */
>> +#define SETUP_MS            1000
>> +
>>   enum {
>>       TPS_PORTINFO_SINK,
>>       TPS_PORTINFO_SINK_ACCESSORY,
>> @@ -86,6 +90,7 @@ struct tps6598x {
>>       struct mutex lock; /* device lock */
>>       u8 i2c_protocol:1;
>>   +    struct gpio_desc *reset;
>>       struct typec_port *port;
>>       struct typec_partner *partner;
>>       struct usb_pd_identity partner_identity;
>> @@ -717,6 +722,13 @@ static int tps6598x_probe(struct i2c_client *client)
>>       mutex_init(&tps->lock);
>>       tps->dev = &client->dev;
>>   +    tps->reset = devm_gpiod_get_optional(tps->dev, "reset",
>> GPIOD_OUT_LOW);
>> +    if (IS_ERR(tps->reset))
>> +        return dev_err_probe(tps->dev, PTR_ERR(tps->reset),
>> +                     "failed to get reset GPIO\n");
>> +    if (tps->reset)
>> +        msleep(SETUP_MS);
>> +
> 
> This looks a bit odd to me, shouldn't you drive reset to zero ?
> 
> if (tps->reset) {
>     gpiod_set_value_cansleep(tps->reset, 0);
>     msleep(SETUP_MS);
> }
> 
The reset line is driven to zero by means fo the GPIOD_OUT_LOW flag, so
there is no need to set it explicitly again.

> also wouldn't it make sense to functionally decompose that and reuse in
> probe() and tps6598x_resume() ?
> 
> tps6598x_reset() {
>     if (tps->reset) {
>         gpiod_set_value_cansleep(tps->reset, 0);
>         msleep(SETUP_MS);
>     }
> }
> 
I can move the reset action to a separate function as you proposed, but
then I suppose it would make sense to use the same function for both
reset levels. Maybe something like:

tps6598x_reset(bool level) {
    if (tps->reset) {
        gpiod_set_value_cansleep(tps->reset, level);
	if (!level)
            msleep(SETUP_MS);
    }
}

> ---
> bod
Thanks for your feedback.

Best regards,
Javier Carrasco