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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>
This commit is contained in:
Chris Packham 2016-05-13 15:19:31 +12:00 committed by Heiko Schocher
parent 3a3705280d
commit d6b7757e41
1 changed files with 29 additions and 33 deletions
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62
drivers/i2c/mvtwsi.c
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@ -184,27 +184,18 @@ static int twsi_wait(struct i2c_adapter *adap, int expected_status)
MVTWSI_ERROR_TIMEOUT, control, status, 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 * Assert the START condition, either in a single I2C transaction
* or inside back-to-back ones (repeated starts). * 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); struct mvtwsi_registers *twsi = twsi_get_base(adap);
/* globally set TWSIEN in case it was not */ /* globally set TWSIEN in case it was not */
twsi_control_flags |= MVTWSI_CONTROL_TWSIEN; *flags |= MVTWSI_CONTROL_TWSIEN;
/* assert START */ /* assert START */
writel(twsi_control_flags | MVTWSI_CONTROL_START | writel(*flags | MVTWSI_CONTROL_START |
MVTWSI_CONTROL_CLEAR_IFLG, &twsi->control); MVTWSI_CONTROL_CLEAR_IFLG, &twsi->control);
/* wait for controller to process START */ /* wait for controller to process START */
return twsi_wait(adap, expected_status); 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). * 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); struct mvtwsi_registers *twsi = twsi_get_base(adap);
/* put byte in data register for sending */ /* put byte in data register for sending */
writel(byte, &twsi->data); writel(byte, &twsi->data);
/* clear any pending interrupt -- that'll cause sending */ /* 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 */ /* wait for controller to receive byte and check ACK */
return twsi_wait(adap, expected_status); 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. * Receive a byte.
* Global mvtwsi_control_flags variable says if we should ack or nak. * 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); struct mvtwsi_registers *twsi = twsi_get_base(adap);
int expected_status, status; int expected_status, status;
/* compute expected status based on ACK bit in global control flags */ /* 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; expected_status = MVTWSI_STATUS_DATA_R_ACK;
else else
expected_status = MVTWSI_STATUS_DATA_R_NAK; expected_status = MVTWSI_STATUS_DATA_R_NAK;
/* acknowledge *previous state* and launch receive */ /* 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 */ /* wait for controller to receive byte and assert ACK or NAK */
status = twsi_wait(adap, expected_status); status = twsi_wait(adap, expected_status);
/* if we did receive expected byte then store it */ /* 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) static void twsi_reset(struct i2c_adapter *adap)
{ {
struct mvtwsi_registers *twsi = twsi_get_base(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 */ /* reset controller */
writel(0, &twsi->soft_reset); writel(0, &twsi->soft_reset);
/* wait 2 ms -- this is what the Marvell LSP does */ /* 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. * Expected address status will derive from direction bit (bit 0) in addr.
*/ */
static int i2c_begin(struct i2c_adapter *adap, int expected_start_status, static int i2c_begin(struct i2c_adapter *adap, int expected_start_status,
u8 addr) u8 addr, u8 *flags)
{ {
int status, expected_addr_status; int status, expected_addr_status;
@ -363,10 +354,11 @@ static int i2c_begin(struct i2c_adapter *adap, int expected_start_status,
else /* writing */ else /* writing */
expected_addr_status = MVTWSI_STATUS_ADDR_W_ACK; expected_addr_status = MVTWSI_STATUS_ADDR_W_ACK;
/* assert START */ /* 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 */ /* send out the address if the start went well */
if (status == 0) 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 ok or status of first failure to caller */
return status; 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) static int twsi_i2c_probe(struct i2c_adapter *adap, uchar chip)
{ {
u8 dummy_byte; u8 dummy_byte;
u8 flags = 0;
int status; int status;
/* begin i2c read */ /* 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. */ /* dummy read was accepted: receive byte but NAK it. */
if (status == 0) if (status == 0)
status = twsi_recv(adap, &dummy_byte); status = twsi_recv(adap, &dummy_byte, &flags);
/* Stop transaction */ /* Stop transaction */
twsi_stop(adap, 0); twsi_stop(adap, 0);
/* return 0 or status of first failure */ /* 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 alen, uchar *data, int length)
{ {
int status; int status;
u8 flags = 0;
/* begin i2c write to send the address bytes */ /* 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 */ /* send addr bytes */
while ((status == 0) && alen--) while ((status == 0) && alen--)
status = twsi_send(adap, addr >> (8*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 */ /* begin i2c read to receive eeprom data bytes */
if (status == 0) if (status == 0)
status = i2c_begin(adap, MVTWSI_STATUS_REPEATED_START, 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 */ /* prepare ACK if at least one byte must be received */
if (length > 0) if (length > 0)
twsi_control_flags |= MVTWSI_CONTROL_ACK; flags |= MVTWSI_CONTROL_ACK;
/* now receive actual bytes */ /* now receive actual bytes */
while ((status == 0) && length--) { while ((status == 0) && length--) {
/* reset NAK if we if no more to read now */ /* reset NAK if we if no more to read now */
if (length == 0) if (length == 0)
twsi_control_flags &= ~MVTWSI_CONTROL_ACK; flags &= ~MVTWSI_CONTROL_ACK;
/* read current byte */ /* read current byte */
status = twsi_recv(adap, data++); status = twsi_recv(adap, data++, &flags);
} }
/* Stop transaction */ /* Stop transaction */
status = twsi_stop(adap, status); 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 alen, uchar *data, int length)
{ {
int status; int status;
u8 flags = 0;
/* begin i2c write to send the eeprom adress bytes then data bytes */ /* 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 */ /* send addr bytes */
while ((status == 0) && alen--) while ((status == 0) && alen--)
status = twsi_send(adap, addr >> (8*alen), status = twsi_send(adap, addr >> (8*alen),
MVTWSI_STATUS_DATA_W_ACK); MVTWSI_STATUS_DATA_W_ACK, &flags);
/* send data bytes */ /* send data bytes */
while ((status == 0) && (length-- > 0)) 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 */ /* Stop transaction */
status = twsi_stop(adap, status); status = twsi_stop(adap, status);
/* return 0 or status of first failure */ /* return 0 or status of first failure */