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From:   Kevin Paul Herbert <kph@platinasystems.com>
To:     biwen.li@nxp.com, leoyang.li@nxp.com, linux@rempel-privat.de,
        kernel@pengutronix.de, wsa@the-dreams.de, shawnguo@kernel.org,
        s.hauer@pengutronix.de, festevam@gmail.com, aisheng.dong@nxp.com,
        xiaoning.wang@nxp.com, o.rempel@pengutronix.de,
        linux-i2c@vger.kernel.org, linux-kernel@vger.kernel.org,
        jiafei.pan@nxp.com, xiaobo.xie@nxp.com,
        linux-arm-kernel@lists.infradead.org, biwen.li@oss.nxp.com,
        kph@platinasystems.com
Subject: [PATCH] i2c-imx.c: Synthesize end of transaction events without idle interrupts
Date:   Tue, 22 Dec 2020 11:48:50 -0800
Message-Id: <20201222194850.2274527-1-kph@platinasystems.com>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Precedence: bulk

Only the Layerscape SoCs have interrupts on bus idle, which facilitate
sending events which complete slave bus transactions.

Add support for synthesizing missing events. If we see a master request,
or a newly addressed slave request, if the last event sent to the backend
was I2C_SLAVE_READ_REQUESTED, send the backend a I2C_SLAVE_READ_PROCESSED
followed by I2C_SLAVE_STOP. For all other events, send an I2C_SLAVE_STOP.

Signed-off-by: Kevin Paul Herbert <kph@platinasystems.com>
---
 drivers/i2c/busses/i2c-imx.c | 59 +++++++++++++++++++++++++++++++-----
 1 file changed, 52 insertions(+), 7 deletions(-)

diff --git a/drivers/i2c/busses/i2c-imx.c b/drivers/i2c/busses/i2c-imx.c
index b444fbf1a262..b3e2a6a7fc19 100644
--- a/drivers/i2c/busses/i2c-imx.c
+++ b/drivers/i2c/busses/i2c-imx.c
@@ -209,6 +209,7 @@ struct imx_i2c_struct {
 
 	struct imx_i2c_dma	*dma;
 	struct i2c_client	*slave;
+	enum i2c_slave_event last_slave_event;
 };
 
 static const struct imx_i2c_hwdata imx1_i2c_hwdata = {
@@ -662,6 +663,36 @@ static void i2c_imx_enable_bus_idle(struct imx_i2c_struct *i2c_imx)
 	}
 }
 
+static void i2c_imx_slave_event(struct imx_i2c_struct *i2c_imx,
+				enum i2c_slave_event event, u8 *val)
+{
+	i2c_slave_event(i2c_imx->slave, event, val);
+	i2c_imx->last_slave_event = event;
+}
+
+static void i2c_imx_slave_finish_op(struct imx_i2c_struct *i2c_imx)
+{
+	u8 val;
+
+	while (i2c_imx->last_slave_event != I2C_SLAVE_STOP) {
+		switch (i2c_imx->last_slave_event) {
+		case I2C_SLAVE_READ_REQUESTED:
+			i2c_imx_slave_event(i2c_imx, I2C_SLAVE_READ_PROCESSED,
+					    &val);
+			break;
+
+		case I2C_SLAVE_WRITE_REQUESTED:
+		case I2C_SLAVE_READ_PROCESSED:
+		case I2C_SLAVE_WRITE_RECEIVED:
+			i2c_imx_slave_event(i2c_imx, I2C_SLAVE_STOP, &val);
+			break;
+
+		case I2C_SLAVE_STOP:
+			break;
+		}
+	}
+}
+
 static irqreturn_t i2c_imx_slave_isr(struct imx_i2c_struct *i2c_imx,
 				     unsigned int status, unsigned int ctl)
 {
@@ -674,9 +705,11 @@ static irqreturn_t i2c_imx_slave_isr(struct imx_i2c_struct *i2c_imx,
 	}
 
 	if (status & I2SR_IAAS) { /* Addressed as a slave */
+		i2c_imx_slave_finish_op(i2c_imx);
 		if (status & I2SR_SRW) { /* Master wants to read from us*/
 			dev_dbg(&i2c_imx->adapter.dev, "read requested");
-			i2c_slave_event(i2c_imx->slave, I2C_SLAVE_READ_REQUESTED, &value);
+			i2c_imx_slave_event(i2c_imx,
+					    I2C_SLAVE_READ_REQUESTED, &value);
 
 			/* Slave transmit */
 			ctl |= I2CR_MTX;
@@ -686,7 +719,8 @@ static irqreturn_t i2c_imx_slave_isr(struct imx_i2c_struct *i2c_imx,
 			imx_i2c_write_reg(value, i2c_imx, IMX_I2C_I2DR);
 		} else { /* Master wants to write to us */
 			dev_dbg(&i2c_imx->adapter.dev, "write requested");
-			i2c_slave_event(i2c_imx->slave,	I2C_SLAVE_WRITE_REQUESTED, &value);
+			i2c_imx_slave_event(i2c_imx,
+					    I2C_SLAVE_WRITE_REQUESTED, &value);
 
 			/* Slave receive */
 			ctl &= ~I2CR_MTX;
@@ -697,17 +731,20 @@ static irqreturn_t i2c_imx_slave_isr(struct imx_i2c_struct *i2c_imx,
 	} else if (!(ctl & I2CR_MTX)) { /* Receive mode */
 		if (status & I2SR_IBB) { /* No STOP signal detected */
 			value = imx_i2c_read_reg(i2c_imx, IMX_I2C_I2DR);
-			i2c_slave_event(i2c_imx->slave,	I2C_SLAVE_WRITE_RECEIVED, &value);
+			i2c_imx_slave_event(i2c_imx,
+					    I2C_SLAVE_WRITE_RECEIVED, &value);
 		} else { /* STOP signal is detected */
 			dev_dbg(&i2c_imx->adapter.dev,
 				"STOP signal detected");
-			i2c_slave_event(i2c_imx->slave, I2C_SLAVE_STOP, &value);
+			i2c_imx_slave_event(i2c_imx,
+					    I2C_SLAVE_STOP, &value);
 		}
 	} else if (!(status & I2SR_RXAK)) { /* Transmit mode received ACK */
 		ctl |= I2CR_MTX;
 		imx_i2c_write_reg(ctl, i2c_imx, IMX_I2C_I2CR);
 
-		i2c_slave_event(i2c_imx->slave,	I2C_SLAVE_READ_PROCESSED, &value);
+		i2c_imx_slave_event(i2c_imx,
+				    I2C_SLAVE_READ_PROCESSED, &value);
 
 		imx_i2c_write_reg(value, i2c_imx, IMX_I2C_I2DR);
 	} else { /* Transmit mode received NAK */
@@ -748,6 +785,7 @@ static int i2c_imx_reg_slave(struct i2c_client *client)
 		return -EBUSY;
 
 	i2c_imx->slave = client;
+	i2c_imx->last_slave_event = I2C_SLAVE_STOP;
 
 	/* Resume */
 	ret = pm_runtime_get_sync(i2c_imx->adapter.dev.parent);
@@ -800,10 +838,17 @@ static irqreturn_t i2c_imx_isr(int irq, void *dev_id)
 
 	status = imx_i2c_read_reg(i2c_imx, IMX_I2C_I2SR);
 	ctl = imx_i2c_read_reg(i2c_imx, IMX_I2C_I2CR);
+
 	if (status & I2SR_IIF) {
 		i2c_imx_clear_irq(i2c_imx, I2SR_IIF);
-		if (i2c_imx->slave && !(ctl & I2CR_MSTA))
-			return i2c_imx_slave_isr(i2c_imx, status, ctl);
+		if (i2c_imx->slave) {
+			if (!(ctl & I2CR_MSTA)) {
+				return i2c_imx_slave_isr(i2c_imx, status, ctl);
+			} else if (i2c_imx->last_slave_event !=
+				   I2C_SLAVE_STOP) {
+				i2c_imx_slave_finish_op(i2c_imx);
+			}
+		}
 		return i2c_imx_master_isr(i2c_imx, status);
 	}
 
-- 
2.25.1