linux-kernel - Re: [PATCH] usb: typec: tcpm: Fix SINK_DISCOVERY current limit for Rp-default

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Date:   Mon, 10 May 2021 15:07:26 -0700
From:   Guenter Roeck <linux@...ck-us.net>
To:     Badhri Jagan Sridharan <badhri@...gle.com>,
        Heikki Krogerus <heikki.krogerus@...ux.intel.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org,
        Kyle Tso <kyletso@...gle.com>
Subject: Re: [PATCH] usb: typec: tcpm: Fix SINK_DISCOVERY current limit for
 Rp-default

On 5/10/21 2:17 PM, Badhri Jagan Sridharan wrote:
> This is a regression introduced by
> <1373fefc6243cc96b3565f0ffffadfac4ccfb977>
> "Allow slow charging loops to comply to pSnkStby".
> 
> When Source advertises Rp-default, tcpm would request 500mA when in
> SINK_DISCOVERY, Type-C spec advises the sink to follow BC1.2 current
> limits when Rp-default is advertised.
> [12750.503381] Requesting mux state 1, usb-role 2, orientation 1
> [12750.503837] state change SNK_ATTACHED -> SNK_STARTUP [rev3 NONE_AMS]
> [12751.003891] state change SNK_STARTUP -> SNK_DISCOVERY
> [12751.003900] Setting voltage/current limit 5000 mV 500 mA
> 
> This patch restores the behavior where the tcpm would request 0mA when
> Rp-default is advertised by the source.
> [   73.174252] Requesting mux state 1, usb-role 2, orientation 1
> [   73.174749] state change SNK_ATTACHED -> SNK_STARTUP [rev3 NONE_AMS]
> [   73.674800] state change SNK_STARTUP -> SNK_DISCOVERY
> [   73.674808] Setting voltage/current limit 5000 mV 0 mA
> 
> During SNK_DISCOVERY, Cap the current limit to PD_P_SNK_STDBY_MW / 5 only
> for slow_charger_loop case.
> 
> Fixes: 1373fefc6243 ("Allow slow charging loops to comply to pSnkStby")
> Signed-off-by: Badhri Jagan Sridharan <badhri@...gle.com>

Reviewed-by: Guenter Roeck <linux@...ck-us.net>

> ---
>   drivers/usb/typec/tcpm/tcpm.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/usb/typec/tcpm/tcpm.c b/drivers/usb/typec/tcpm/tcpm.c
> index c4fdc00a3bc8..a73299a08ef7 100644
> --- a/drivers/usb/typec/tcpm/tcpm.c
> +++ b/drivers/usb/typec/tcpm/tcpm.c
> @@ -4055,7 +4055,7 @@ static void run_state_machine(struct tcpm_port *port)
>   		if (port->vbus_present) {
>   			u32 current_lim = tcpm_get_current_limit(port);
>   
> -			if (port->slow_charger_loop || (current_lim > PD_P_SNK_STDBY_MW / 5))
> +			if (port->slow_charger_loop && (current_lim > PD_P_SNK_STDBY_MW / 5))
>   				current_lim = PD_P_SNK_STDBY_MW / 5;
>   			tcpm_set_current_limit(port, current_lim, 5000);
>   			tcpm_set_charge(port, true);
>