i2c: mpc: Correct I2C reset procedure

BugLink: https://bugs.launchpad.net/bugs/1960566

[ Upstream commit ebe82cf ]

Current I2C reset procedure is broken in two ways:
1) It only generate 1 START instead of 9 STARTs and STOP.
2) It leaves the bus Busy so every I2C xfer after the first
   fixup calls the reset routine again, for every xfer there after.

This fixes both errors.

Signed-off-by: Joakim Tjernlund <joakim.tjernlund@infinera.com>
Acked-by: Scott Wood <oss@buserror.net>
Signed-off-by: Wolfram Sang <wsa@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>

Author: Joakim Tjernlund

drivers/i2c/busses/i2c-mpc.c

@@ -105,23 +105,30 @@ static irqreturn_t mpc_i2c_isr(int irq, void *dev_id)
 /* Sometimes 9th clock pulse isn't generated, and slave doesn't release
  * the bus, because it wants to send ACK.
  * Following sequence of enabling/disabling and sending start/stop generates
- * the 9 pulses, so it's all OK.
+ * the 9 pulses, each with a START then ending with STOP, so it's all OK.
  */
 static void mpc_i2c_fixup(struct mpc_i2c *i2c)
 {
 	int k;
-	u32 delay_val = 1000000 / i2c->real_clk + 1;
-
-	if (delay_val < 2)
-		delay_val = 2;
+	unsigned long flags;
 
 	for (k = 9; k; k--) {
 		writeccr(i2c, 0);
-		writeccr(i2c, CCR_MSTA | CCR_MTX | CCR_MEN);
+		writeb(0, i2c->base + MPC_I2C_SR); /* clear any status bits */
+		writeccr(i2c, CCR_MEN | CCR_MSTA); /* START */
+		readb(i2c->base + MPC_I2C_DR); /* init xfer */
+		udelay(15); /* let it hit the bus */
+		local_irq_save(flags); /* should not be delayed further */
+		writeccr(i2c, CCR_MEN | CCR_MSTA | CCR_RSTA); /* delay SDA */
 		readb(i2c->base + MPC_I2C_DR);
-		writeccr(i2c, CCR_MEN);
-		udelay(delay_val << 1);
+		if (k != 1)
+			udelay(5);
+		local_irq_restore(flags);
 	}
+	writeccr(i2c, CCR_MEN); /* Initiate STOP */
+	readb(i2c->base + MPC_I2C_DR);
+	udelay(15); /* Let STOP propagate */
+	writeccr(i2c, 0);
 }
 
 static int i2c_wait(struct mpc_i2c *i2c, unsigned timeout, int writing)