linux-kernel - [PATCH v2] usb: typec: tcpm: Report back negotiated PPS voltage and current

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Date:   Mon, 8 Oct 2018 13:53:59 +0100
From:   Adam Thomson <Adam.Thomson.Opensource@...semi.com>
To:     Guenter Roeck <linux@...ck-us.net>,
        Heikki Krogerus <heikki.krogerus@...ux.intel.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
CC:     <linux-usb@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <support.opensource@...semi.com>
Subject: [PATCH v2] usb: typec: tcpm: Report back negotiated PPS voltage and
 current

Currently when requesting a specific voltage or current through
the psy interface, for PPS, when reading back from that interface
the values will always be the same as previously given, if the
request was successful. However PPS only allows for 20mV voltage
steps and 50mA current steps, and the psy class expects microvolt
and micro amp requests, so inbetween values can be provided through
this interface. Really when reading back the true values negotiated
should be given, and not the ones originally asked for.

To report the actual values negotiated with the Source, the values
stored are now rounded down to the relevant step units prior to
building the PPS request, so that those values are later correctly
reported through the psy interface. In addition this improves the
adjustments made to meet the operating power requirements of the
platform, which previously could have been slightly out due to not
using valid PPS units of voltage and current.

Signed-off-by: Adam Thomson <Adam.Thomson.Opensource@...semi.com>
---
Changes are based on usb-testing (e7a2c3fa2857)

Changes in v2:
 - Rounding down of PPS voltage and current values moved to relevant API
   functions so stored values are correctly updated prior to all subsequent
   usage and decision making, as discuessed with Guenter.

 drivers/usb/typec/tcpm/tcpm.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/drivers/usb/typec/tcpm/tcpm.c b/drivers/usb/typec/tcpm/tcpm.c
index b06eac8..dbbd71f 100644
--- a/drivers/usb/typec/tcpm/tcpm.c
+++ b/drivers/usb/typec/tcpm/tcpm.c
@@ -4113,6 +4113,9 @@ static int tcpm_pps_set_op_curr(struct tcpm_port *port, u16 op_curr)
 		goto port_unlock;
 	}

+	/* Round down operating current to align with PPS valid steps */
+	op_curr = op_curr - (op_curr % RDO_PROG_CURR_MA_STEP);
+
 	reinit_completion(&port->pps_complete);
 	port->pps_data.op_curr = op_curr;
 	port->pps_status = 0;
@@ -4166,6 +4169,9 @@ static int tcpm_pps_set_out_volt(struct tcpm_port *port, u16 out_volt)
 		goto port_unlock;
 	}

+	/* Round down output voltage to align with PPS valid steps */
+	out_volt = out_volt - (out_volt % RDO_PROG_VOLT_MV_STEP);
+
 	reinit_completion(&port->pps_complete);
 	port->pps_data.out_volt = out_volt;
 	port->pps_status = 0;
-- 
1.9.1