hw/p8-i2c: Clean up interrupt masking

There's three interrupt registers defined for the I2C master:

1. Interrupt mask
2. Raw interrupt condition bits
3. Masked interrupt condition bits

All the I2C master interrupts are LSIs so the raw condition bits will only
go to zero if the interrupt condition is dealt with. As a result the
latter two registers are read only. For writes their addresses are
re-used as atomic OR and atomic AND update registers for the mask
register.

When unmasking interrupts we currently do that via the atomic OR
register and mask via the atomic AND, but we use the interrupt condition
register macro names. This is a bit confusing and the documentation
isn't super clear about the behaviour so fix the macro names in favour
of something saner.

Signed-off-by: Oliver O'Halloran <oohall@gmail.com>

hw/p8-i2c.c

@@ -92,10 +92,23 @@ DEFINE_LOG_ENTRY(OPAL_RC_I2C_RESET, OPAL_INPUT_OUTPUT_ERR_EVT, OPAL_I2C,
 #define I2C_WATERMARK_HIGH		PPC_BITMASK(16, 19)
 #define I2C_WATERMARK_LOW		PPC_BITMASK(24, 27)
 
-/* I2C interrupt mask, condition and interrupt registers */
+/*
+ * I2C interrupt mask and condition registers
+ *
+ * NB: The function of 0x9 and 0xa changes depending on whether you're reading
+ *     or writing to them. When read they return the interrupt condition bits
+ *     and on writes they update the interrupt mask register.
+ *
+ *  The bit definitions are the same for all the interrupt registers.
+ */
 #define I2C_INTR_MASK_REG		0x8
-#define I2C_INTR_COND_REG		0x9
-#define I2C_INTR_REG			0xa
+
+#define I2C_INTR_RAW_COND_REG 		0x9 /* read */
+#define I2C_INTR_MASK_OR_REG		0x9 /* write*/
+
+#define I2C_INTR_COND_REG 		0xa /* read */
+#define I2C_INTR_MASK_AND_REG		0xa /* write */
+
 #define I2C_INTR_ALL			PPC_BITMASK(16, 31)
 #define I2C_INTR_INVALID_CMD		PPC_BIT(16)
 #define I2C_INTR_LBUS_PARITY_ERR	PPC_BIT(17)
@@ -140,6 +153,10 @@ DEFINE_LOG_ENTRY(OPAL_RC_I2C_RESET, OPAL_INPUT_OUTPUT_ERR_EVT, OPAL_I2C,
 			  I2C_STAT_BKEND_ACCESS_ERR | I2C_STAT_ARBT_LOST_ERR | \
 			  I2C_STAT_NACK_RCVD_ERR | I2C_STAT_STOP_ERR)
 
+
+#define I2C_INTR_ACTIVE \
+	((I2C_STAT_ANY_ERR >> 16) | I2C_INTR_CMD_COMP | I2C_INTR_DATA_REQ)
+
 /* Pseudo-status used for timeouts */
 #define I2C_STAT_PSEUDO_TIMEOUT		PPC_BIT(63)
 
@@ -264,7 +281,7 @@ static void p8_i2c_print_debug_info(struct p8_i2c_master_port *port,
 	i2cm_read_reg(master, I2C_STAT_REG, &stat);
 	i2cm_read_reg(master, I2C_EXTD_STAT_REG, &estat);
 	i2cm_read_reg(master, I2C_INTR_MASK_REG, &intm);
-	i2cm_read_reg(master, I2C_INTR_COND_REG, &intc);
+	i2cm_read_reg(master, I2C_INTR_RAW_COND_REG, &intc);
 
 	log_simple_error(&e_info(OPAL_RC_I2C_TRANSFER), "I2C: Register dump--\n"
 			 "    cmd:0x%016llx\tmode:0x%016llx\tstat:0x%016llx\n"
@@ -317,10 +334,8 @@ static int p8_i2c_enable_irqs(struct p8_i2c_master *master)
 {
 	int rc;
 
-	/* Enable the interrupts */
-	rc = xscom_write(master->chip_id, master->xscom_base +
-			 I2C_INTR_COND_REG, I2C_STAT_ANY_ERR >> 16 |
-			 I2C_INTR_CMD_COMP | I2C_INTR_DATA_REQ);
+	/* enable interrupts we're interested in */
+	rc = i2cm_write_reg(master, I2C_INTR_MASK_OR_REG, I2C_INTR_ACTIVE);
 	if (rc)
 		prlog(PR_ERR, "I2C: Failed to enable the interrupts\n");
 
@@ -802,8 +817,8 @@ static void p8_i2c_check_status(struct p8_i2c_master *master)
 		return;
 	}
 
-	/* Mask the interrupts for this engine */
-	rc = i2cm_write_reg(master, I2C_INTR_REG, ~I2C_INTR_ALL);
+	/* mask interrupts while we're mucking with the master */
+	rc = i2cm_write_reg(master, I2C_INTR_MASK_AND_REG, ~I2C_INTR_ALL);
 	if (rc) {
 		log_simple_error(&e_info(OPAL_RC_I2C_TRANSFER),
 			"I2C: Failed to disable the interrupts\n");