From 6305020526cee4adcedec1fc64f901a6f0eb6406 Mon Sep 17 00:00:00 2001
From: Andriy Gapon <avg@FreeBSD.org>
Date: Mon, 7 Sep 2020 06:32:03 +0000
Subject: [PATCH] twsi: some variants clear interrupt flag by writing 0, others
 by writing 1

Make that distinction more explicit and regular in the code.
The difference in behavior is documented in the respective datasheets.

Previously, the code handled the distinction by writing the control
register multiple times where at least one write was zero and another
was one.

This can be considered a follow-up to r363021.

Reviewed by:	manu
MFC after:	4 weeks
Differential Revision: https://reviews.freebsd.org/D26308
---
 sys/dev/iicbus/twsi/a10_twsi.c |  4 ++++
 sys/dev/iicbus/twsi/twsi.c     | 16 +++++++++-------
 sys/dev/iicbus/twsi/twsi.h     |  1 +
 3 files changed, 14 insertions(+), 7 deletions(-)

diff --git a/sys/dev/iicbus/twsi/a10_twsi.c b/sys/dev/iicbus/twsi/a10_twsi.c
index e70e33fbe229..17f551f27234 100644
--- a/sys/dev/iicbus/twsi/a10_twsi.c
+++ b/sys/dev/iicbus/twsi/a10_twsi.c
@@ -122,6 +122,10 @@ a10_twsi_attach(device_t dev)
 	sc->reg_soft_reset = TWI_SRST;
 
 	sc->need_ack = true;
+
+	if (ofw_bus_is_compatible(dev, "allwinner,sun6i-a31-i2c") ||
+	    ofw_bus_is_compatible(dev, "allwinner,sun6i-a83t-i2c"))
+		sc->iflag_w1c = true;
 	return (twsi_attach(dev));
 }
 
diff --git a/sys/dev/iicbus/twsi/twsi.c b/sys/dev/iicbus/twsi/twsi.c
index 9d1a17f43103..a606c2aefd36 100644
--- a/sys/dev/iicbus/twsi/twsi.c
+++ b/sys/dev/iicbus/twsi/twsi.c
@@ -147,7 +147,11 @@ twsi_clear_iflg(struct twsi_softc *sc)
 {
 
 	DELAY(1000);
-	twsi_control_clear(sc, TWSI_CONTROL_IFLG);
+	/* There are two ways of clearing IFLAG. */
+	if (sc->iflag_w1c)
+		twsi_control_set(sc, TWSI_CONTROL_IFLG);
+	else
+		twsi_control_clear(sc, TWSI_CONTROL_IFLG);
 	DELAY(1000);
 }
 
@@ -667,13 +671,11 @@ twsi_intr(void *arg)
 	}
 	debugf(sc->dev, "Refresh reg_control\n");
 
-	/* 
-	 * Fix silicon bug on > Allwinner A20 by doing a read and writing
-	 * again to the control register
+	/*
+	 * Newer Allwinner chips clear IFLG after writing 1 to it.
 	 */
-	status = TWSI_READ(sc, sc->reg_status);
-	TWSI_WRITE(sc, sc->reg_control,
-	  sc->control_val | TWSI_CONTROL_IFLG);
+	TWSI_WRITE(sc, sc->reg_control, sc->control_val |
+	    (sc->iflag_w1c ? TWSI_CONTROL_IFLG : 0));
 
 	debugf(sc->dev, "Done with interrupts\n\n");
 	if (transfer_done == 1) {
diff --git a/sys/dev/iicbus/twsi/twsi.h b/sys/dev/iicbus/twsi/twsi.h
index a0c4958b47de..631486fb3f0c 100644
--- a/sys/dev/iicbus/twsi/twsi.h
+++ b/sys/dev/iicbus/twsi/twsi.h
@@ -66,6 +66,7 @@ struct twsi_softc {
 	int			error;
 	uint32_t		control_val;
 	bool			need_ack;
+	bool			iflag_w1c;
 
 	bus_size_t	reg_data;
 	bus_size_t	reg_slave_addr;