i2c: mvtwsi: Eliminate twsi_control_flags

In a system where the initial u-boot location is genuinely NOR flash (as
opposed to RAM or a cache-line setup by a pre-bootloader) writes to the
data section are problematic. At best these writes have no effect, at
worst they put the flash memory into a status mode which changes the
executable code underneath us.

Pass around a stack variable from the top of the twsi i2c driver to
avoid writing to global data.

Signed-off-by: Chris Packham <judge.packham@gmail.com>

diff --git a/drivers/i2c/mvtwsi.c b/drivers/i2c/mvtwsi.c
index 221ff4fe7afa02b39c56a5cd12a1cf359ae975ac..bf4443287fd2977fe3a61f3f653327ab3e013323 100644 (file)
--- a/drivers/i2c/mvtwsi.c
+++ b/drivers/i2c/mvtwsi.c
@@ -184,27 +184,18 @@ static int twsi_wait(struct i2c_adapter *adap, int expected_status)
                MVTWSI_ERROR_TIMEOUT, control, status, expected_status);
 }
 
-/*
- * These flags are ORed to any write to the control register
- * They allow global setting of TWSIEN and ACK.
- * By default none are set.
- * twsi_start() sets TWSIEN (in case the controller was disabled)
- * twsi_recv() sets ACK or resets it depending on expected status.
- */
-static u8 twsi_control_flags = MVTWSI_CONTROL_TWSIEN;
-
 /*
  * Assert the START condition, either in a single I2C transaction
  * or inside back-to-back ones (repeated starts).
  */
-static int twsi_start(struct i2c_adapter *adap, int expected_status)
+static int twsi_start(struct i2c_adapter *adap, int expected_status, u8 *flags)
 {
        struct mvtwsi_registers *twsi = twsi_get_base(adap);
 
        /* globally set TWSIEN in case it was not */
-       twsi_control_flags |= MVTWSI_CONTROL_TWSIEN;
+       *flags |= MVTWSI_CONTROL_TWSIEN;
        /* assert START */
-       writel(twsi_control_flags | MVTWSI_CONTROL_START |
+       writel(*flags | MVTWSI_CONTROL_START |
                                    MVTWSI_CONTROL_CLEAR_IFLG, &twsi->control);
        /* wait for controller to process START */
        return twsi_wait(adap, expected_status);
@@ -213,14 +204,15 @@ static int twsi_start(struct i2c_adapter *adap, int expected_status)
 /*
  * Send a byte (i2c address or data).
  */
-static int twsi_send(struct i2c_adapter *adap, u8 byte, int expected_status)
+static int twsi_send(struct i2c_adapter *adap, u8 byte, int expected_status,
+                    u8 *flags)
 {
        struct mvtwsi_registers *twsi = twsi_get_base(adap);
 
        /* put byte in data register for sending */
        writel(byte, &twsi->data);
        /* clear any pending interrupt -- that'll cause sending */
-       writel(twsi_control_flags | MVTWSI_CONTROL_CLEAR_IFLG, &twsi->control);
+       writel(*flags | MVTWSI_CONTROL_CLEAR_IFLG, &twsi->control);
        /* wait for controller to receive byte and check ACK */
        return twsi_wait(adap, expected_status);
 }
@@ -229,18 +221,18 @@ static int twsi_send(struct i2c_adapter *adap, u8 byte, int expected_status)
  * Receive a byte.
  * Global mvtwsi_control_flags variable says if we should ack or nak.
  */
-static int twsi_recv(struct i2c_adapter *adap, u8 *byte)
+static int twsi_recv(struct i2c_adapter *adap, u8 *byte, u8 *flags)
 {
        struct mvtwsi_registers *twsi = twsi_get_base(adap);
        int expected_status, status;
 
        /* compute expected status based on ACK bit in global control flags */
-       if (twsi_control_flags & MVTWSI_CONTROL_ACK)
+       if (*flags & MVTWSI_CONTROL_ACK)
                expected_status = MVTWSI_STATUS_DATA_R_ACK;
        else
                expected_status = MVTWSI_STATUS_DATA_R_NAK;
        /* acknowledge *previous state* and launch receive */
-       writel(twsi_control_flags | MVTWSI_CONTROL_CLEAR_IFLG, &twsi->control);
+       writel(*flags | MVTWSI_CONTROL_CLEAR_IFLG, &twsi->control);
        /* wait for controller to receive byte and assert ACK or NAK */
        status = twsi_wait(adap, expected_status);
        /* if we did receive expected byte then store it */
@@ -296,8 +288,7 @@ static unsigned int twsi_calc_freq(const int n, const int m)
 static void twsi_reset(struct i2c_adapter *adap)
 {
        struct mvtwsi_registers *twsi = twsi_get_base(adap);
-       /* ensure controller will be enabled by any twsi*() function */
-       twsi_control_flags = MVTWSI_CONTROL_TWSIEN;
+
        /* reset controller */
        writel(0, &twsi->soft_reset);
        /* wait 2 ms -- this is what the Marvell LSP does */
@@ -353,7 +344,7 @@ static void twsi_i2c_init(struct i2c_adapter *adap, int speed, int slaveadd)
  * Expected address status will derive from direction bit (bit 0) in addr.
  */
 static int i2c_begin(struct i2c_adapter *adap, int expected_start_status,
-                    u8 addr)
+                    u8 addr, u8 *flags)
 {
        int status, expected_addr_status;
 
@@ -363,10 +354,11 @@ static int i2c_begin(struct i2c_adapter *adap, int expected_start_status,
        else /* writing */
                expected_addr_status = MVTWSI_STATUS_ADDR_W_ACK;
        /* assert START */
-       status = twsi_start(adap, expected_start_status);
+       status = twsi_start(adap, expected_start_status, flags);
        /* send out the address if the start went well */
        if (status == 0)
-               status = twsi_send(adap, addr, expected_addr_status);
+               status = twsi_send(adap, addr, expected_addr_status,
+                                  flags);
        /* return ok or status of first failure to caller */
        return status;
 }
@@ -378,13 +370,14 @@ static int i2c_begin(struct i2c_adapter *adap, int expected_start_status,
 static int twsi_i2c_probe(struct i2c_adapter *adap, uchar chip)
 {
        u8 dummy_byte;
+       u8 flags = 0;
        int status;
 
        /* begin i2c read */
-       status = i2c_begin(adap, MVTWSI_STATUS_START, (chip << 1) | 1);
+       status = i2c_begin(adap, MVTWSI_STATUS_START, (chip << 1) | 1, &flags);
        /* dummy read was accepted: receive byte but NAK it. */
        if (status == 0)
-               status = twsi_recv(adap, &dummy_byte);
+               status = twsi_recv(adap, &dummy_byte, &flags);
        /* Stop transaction */
        twsi_stop(adap, 0);
        /* return 0 or status of first failure */
@@ -405,27 +398,28 @@ static int twsi_i2c_read(struct i2c_adapter *adap, uchar chip, uint addr,
                        int alen, uchar *data, int length)
 {
        int status;
+       u8 flags = 0;
 
        /* begin i2c write to send the address bytes */
-       status = i2c_begin(adap, MVTWSI_STATUS_START, (chip << 1));
+       status = i2c_begin(adap, MVTWSI_STATUS_START, (chip << 1), &flags);
        /* send addr bytes */
        while ((status == 0) && alen--)
                status = twsi_send(adap, addr >> (8*alen),
-                       MVTWSI_STATUS_DATA_W_ACK);
+                       MVTWSI_STATUS_DATA_W_ACK, &flags);
        /* begin i2c read to receive eeprom data bytes */
        if (status == 0)
                status = i2c_begin(adap, MVTWSI_STATUS_REPEATED_START,
-                                  (chip << 1) | 1);
+                                  (chip << 1) | 1, &flags);
        /* prepare ACK if at least one byte must be received */
        if (length > 0)
-               twsi_control_flags |= MVTWSI_CONTROL_ACK;
+               flags |= MVTWSI_CONTROL_ACK;
        /* now receive actual bytes */
        while ((status == 0) && length--) {
                /* reset NAK if we if no more to read now */
                if (length == 0)
-                       twsi_control_flags &= ~MVTWSI_CONTROL_ACK;
+                       flags &= ~MVTWSI_CONTROL_ACK;
                /* read current byte */
-               status = twsi_recv(adap, data++);
+               status = twsi_recv(adap, data++, &flags);
        }
        /* Stop transaction */
        status = twsi_stop(adap, status);
@@ -441,16 +435,18 @@ static int twsi_i2c_write(struct i2c_adapter *adap, uchar chip, uint addr,
                        int alen, uchar *data, int length)
 {
        int status;
+       u8 flags = 0;
 
        /* begin i2c write to send the eeprom adress bytes then data bytes */
-       status = i2c_begin(adap, MVTWSI_STATUS_START, (chip << 1));
+       status = i2c_begin(adap, MVTWSI_STATUS_START, (chip << 1), &flags);
        /* send addr bytes */
        while ((status == 0) && alen--)
                status = twsi_send(adap, addr >> (8*alen),
-                       MVTWSI_STATUS_DATA_W_ACK);
+                       MVTWSI_STATUS_DATA_W_ACK, &flags);
        /* send data bytes */
        while ((status == 0) && (length-- > 0))
-               status = twsi_send(adap, *(data++), MVTWSI_STATUS_DATA_W_ACK);
+               status = twsi_send(adap, *(data++), MVTWSI_STATUS_DATA_W_ACK,
+                                  &flags);
        /* Stop transaction */
        status = twsi_stop(adap, status);
        /* return 0 or status of first failure */