linux-kernel - Re: [PATCH] usb: typec: ucsi: psy: Set current max to 100mA for BC 1.2 and Default

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Message-ID: <aH4MZHvgg1V6u_Bv@kuha.fi.intel.com>
Date: Mon, 21 Jul 2025 12:46:12 +0300
From: Heikki Krogerus <heikki.krogerus@...ux.intel.com>
To: Benson Leung <bleung@...omium.org>
Cc: jthies@...gle.com, gregkh@...uxfoundation.org, hansg@...nel.org,
	sebastian.reichel@...labora.com, dmitry.baryshkov@....qualcomm.com,
	madhu.m@...el.com, linux-usb@...r.kernel.org,
	linux-kernel@...r.kernel.org, bleung@...gle.com
Subject: Re: [PATCH] usb: typec: ucsi: psy: Set current max to 100mA for BC
 1.2 and Default

On Thu, Jul 17, 2025 at 08:08:05PM +0000, Benson Leung wrote:
> ucsi_psy_get_current_max would return 0mA as the maximum current if
> UCSI detected a BC or a Default USB Power sporce.
> 
> The comment in this function is true that we can't tell the difference
> between DCP/CDP or SDP chargers, but we can guarantee that at least 1-unit
> of USB 1.1/2.0 power is available, which is 100mA, which is a better
> fallback value than 0, which causes some userspaces, including the ChromeOS
> power manager, to regard this as a power source that is not providing
> any power.
> 
> In reality, 100mA is guaranteed from all sources in these classes.
> 
> Signed-off-by: Benson Leung <bleung@...omium.org>

Reviewed-by: Heikki Krogerus <heikki.krogerus@...ux.intel.com>

> ---
>  drivers/usb/typec/ucsi/psy.c  | 2 +-
>  drivers/usb/typec/ucsi/ucsi.h | 7 ++++---
>  2 files changed, 5 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/usb/typec/ucsi/psy.c b/drivers/usb/typec/ucsi/psy.c
> index 62ac69730405..62a9d68bb66d 100644
> --- a/drivers/usb/typec/ucsi/psy.c
> +++ b/drivers/usb/typec/ucsi/psy.c
> @@ -164,7 +164,7 @@ static int ucsi_psy_get_current_max(struct ucsi_connector *con,
>  	case UCSI_CONSTAT_PWR_OPMODE_DEFAULT:
>  	/* UCSI can't tell b/w DCP/CDP or USB2/3x1/3x2 SDP chargers */
>  	default:
> -		val->intval = 0;
> +		val->intval = UCSI_TYPEC_DEFAULT_CURRENT * 1000;
>  		break;
>  	}
>  	return 0;
> diff --git a/drivers/usb/typec/ucsi/ucsi.h b/drivers/usb/typec/ucsi/ucsi.h
> index b711e1ecc378..ebd7c27c2cc7 100644
> --- a/drivers/usb/typec/ucsi/ucsi.h
> +++ b/drivers/usb/typec/ucsi/ucsi.h
> @@ -483,9 +483,10 @@ struct ucsi {
>  #define UCSI_MAX_SVID		5
>  #define UCSI_MAX_ALTMODES	(UCSI_MAX_SVID * 6)
>  
> -#define UCSI_TYPEC_VSAFE5V	5000
> -#define UCSI_TYPEC_1_5_CURRENT	1500
> -#define UCSI_TYPEC_3_0_CURRENT	3000
> +#define UCSI_TYPEC_VSAFE5V		5000
> +#define UCSI_TYPEC_DEFAULT_CURRENT	 100
> +#define UCSI_TYPEC_1_5_CURRENT		1500
> +#define UCSI_TYPEC_3_0_CURRENT		3000
>  
>  struct ucsi_connector {
>  	int num;
> -- 
> 2.50.0.727.gbf7dc18ff4-goog

-- 
heikki