Re: [PATCH v5 4/6] i2c: at91: add support for new alternative command mode

Nicolas Ferre
2015-06-09T16:08:33Z

Le 03/06/2015 18:25, Cyrille Pitchen a écrit :
> The alternative command mode was introduced to simplify the transmission
> of STOP conditions and to solve timing and latency issues around them.
>
> This mode relies on a new register, the Alternative Command Register,
> which must be set at the same time as the Master Mode Register. This new
> register was designed to allow simple setup of basic combined transactions
> built from up to two unitary transactions.
>
> Indeed, the ACR is split into two areas, which describe one unitary
> transaction each. Each area is filled with Data Length 8bit counter, a
> Direction and a PEC Request bit. The PEC bit is only used in SMBus mode
> and is not supported by this driver yet. Also when using alternative
> command mode, the MREAD bit from the Master Mode Register is ignored.
> Instead the Direction bits from ACR are used to setup the direction, read
> or write, of each unitary transaction. Finally the 8bit counters must
> filled with the data length of their respective transaction. Then if only
> one transaction is to be used, the data length of the second one must be
> set to zero. At the moment, this driver uses only the first transaction.
>
> In addition to MMR and ACR, the Control Register also need to be written
> to enable the alternative command mode. That's the purpose of its ACMEN
> bit, which stands for Alternative Command Mode Enable.
>
> Note that the alternative command mode is compatible with the use of the
> Internal Address Register. So combined transactions for eeprom read are
> actually implemented with the Internal Address Register. This register is
> written with up to 3 bytes, which are the internal address sent to the
> slave through the first write transaction. Then the first area of the ACR
> describe the write transaction to follow, which carries the data to be
> read from the eeprom. The second area of the ACR is not used so its Data
> Length 8bit counter is cleared.
>
> For each byte sent or received by the device, the Data Length 8bit counter
> is decremented. When it reaches 0, a STOP condition is automatically sent.
>
> Signed-off-by: Cyrille Pitchen <cyrille.pitchen@atmel.com>
> ---
> drivers/i2c/busses/i2c-at91.c | 121 +++++++++++++++++++++++++++++++++++-------
> 1 file changed, 101 insertions(+), 20 deletions(-)
>
> diff --git a/drivers/i2c/busses/i2c-at91.c b/drivers/i2c/busses/i2c-at91.c
> index 0e88b68..67b4f15 100644
> --- a/drivers/i2c/busses/i2c-at91.c
> +++ b/drivers/i2c/busses/i2c-at91.c
> @@ -49,6 +49,11 @@
> #define AT91_TWI_SVDIS BIT(5) /* Slave Transfer Disable */
> #define AT91_TWI_QUICK BIT(6) /* SMBus quick command */
> #define AT91_TWI_SWRST BIT(7) /* Software Reset */
> +#define AT91_TWI_ACMEN BIT(16) /* Alternative Command Mode Enable */
> +#define AT91_TWI_ACMDIS BIT(17) /* Alternative Command Mode Disable */
> +#define AT91_TWI_THRCLR BIT(24) /* Transmit Holding Register Clear */
> +#define AT91_TWI_RHRCLR BIT(25) /* Receive Holding Register Clear */
> +#define AT91_TWI_LOCKCLR BIT(26) /* Lock Clear */
>
> #define AT91_TWI_MMR 0x0004 /* Master Mode Register */
> #define AT91_TWI_IADRSZ_1 0x0100 /* Internal Device Address Size */
> @@ -65,6 +70,7 @@
> #define AT91_TWI_OVRE BIT(6) /* Overrun Error */
> #define AT91_TWI_UNRE BIT(7) /* Underrun Error */
> #define AT91_TWI_NACK BIT(8) /* Not Acknowledged */
> +#define AT91_TWI_LOCK BIT(23) /* TWI Lock due to Frame Errors */
>
> #define AT91_TWI_INT_MASK \
> (AT91_TWI_TXCOMP | AT91_TWI_RXRDY | AT91_TWI_TXRDY | AT91_TWI_NACK)
> @@ -75,10 +81,15 @@
> #define AT91_TWI_RHR 0x0030 /* Receive Holding Register */
> #define AT91_TWI_THR 0x0034 /* Transmit Holding Register */
>
> +#define AT91_TWI_ACR 0x0040 /* Alternative Command Register */
> +#define AT91_TWI_ACR_DATAL(len) ((len) & 0xff)
> +#define AT91_TWI_ACR_DIR BIT(8)
> +
> struct at91_twi_pdata {
> unsigned clk_max_div;
> unsigned clk_offset;
> bool has_unre_flag;
> + bool has_alt_cmd;
> struct at_dma_slave dma_slave;
> };
>
> @@ -204,7 +215,8 @@ static void at91_twi_write_next_byte(struct at91_twi_dev *dev)
>
> /* send stop when last byte has been written */
> if (--dev->buf_len == 0)
> - at91_twi_write(dev, AT91_TWI_CR, AT91_TWI_STOP);
> + if (!dev->pdata->has_alt_cmd)
> + at91_twi_write(dev, AT91_TWI_CR, AT91_TWI_STOP);
>
> dev_dbg(dev->dev, "wrote 0x%x, to go %d\n", *dev->buf, dev->buf_len);
>
> @@ -226,7 +238,8 @@ static void at91_twi_write_data_dma_callback(void *data)
> * we just have to enable TXCOMP one.
> */
> at91_twi_write(dev, AT91_TWI_IER, AT91_TWI_TXCOMP);
> - at91_twi_write(dev, AT91_TWI_CR, AT91_TWI_STOP);
> + if (!dev->pdata->has_alt_cmd)
> + at91_twi_write(dev, AT91_TWI_CR, AT91_TWI_STOP);
> }
>
> static void at91_twi_write_data_dma(struct at91_twi_dev *dev)
> @@ -302,7 +315,7 @@ static void at91_twi_read_next_byte(struct at91_twi_dev *dev)
> }
>
> /* send stop if second but last byte has been read */
> - if (dev->buf_len == 1)
> + if (!dev->pdata->has_alt_cmd && dev->buf_len == 1)
> at91_twi_write(dev, AT91_TWI_CR, AT91_TWI_STOP);
>
> dev_dbg(dev->dev, "read 0x%x, to go %d\n", *dev->buf, dev->buf_len);
> @@ -313,14 +326,18 @@ static void at91_twi_read_next_byte(struct at91_twi_dev *dev)
> static void at91_twi_read_data_dma_callback(void *data)
> {
> struct at91_twi_dev *dev = (struct at91_twi_dev *)data;
> + unsigned ier = AT91_TWI_TXCOMP;
>
> dma_unmap_single(dev->dev, sg_dma_address(&dev->dma.sg),
> dev->buf_len, DMA_FROM_DEVICE);
>
> - /* The last two bytes have to be read without using dma */
> - dev->buf += dev->buf_len - 2;
> - dev->buf_len = 2;
> - at91_twi_write(dev, AT91_TWI_IER, AT91_TWI_RXRDY | AT91_TWI_TXCOMP);
> + if (!dev->pdata->has_alt_cmd) {
> + /* The last two bytes have to be read without using dma */
> + dev->buf += dev->buf_len - 2;
> + dev->buf_len = 2;
> + ier |= AT91_TWI_RXRDY;
> + }
> + at91_twi_write(dev, AT91_TWI_IER, ier);
> }
>
> static void at91_twi_read_data_dma(struct at91_twi_dev *dev)
> @@ -329,13 +346,14 @@ static void at91_twi_read_data_dma(struct at91_twi_dev *dev)
> struct dma_async_tx_descriptor *rxdesc;
> struct at91_twi_dma *dma = &dev->dma;
> struct dma_chan *chan_rx = dma->chan_rx;
> + size_t buf_len;
>
> + buf_len = (dev->pdata->has_alt_cmd) ? dev->buf_len : dev->buf_len - 2;
> dma->direction = DMA_FROM_DEVICE;
>
> /* Keep in mind that we won't use dma to read the last two bytes */
> at91_twi_irq_save(dev);
> - dma_addr = dma_map_single(dev->dev, dev->buf, dev->buf_len - 2,
> - DMA_FROM_DEVICE);
> + dma_addr = dma_map_single(dev->dev, dev->buf, buf_len, DMA_FROM_DEVICE);
> if (dma_mapping_error(dev->dev, dma_addr)) {
> dev_err(dev->dev, "dma map failed\n");
> return;
> @@ -343,7 +361,7 @@ static void at91_twi_read_data_dma(struct at91_twi_dev *dev)
> dma->buf_mapped = true;
> at91_twi_irq_restore(dev);
> dma->sg.dma_address = dma_addr;
> - sg_dma_len(&dma->sg) = dev->buf_len - 2;
> + sg_dma_len(&dma->sg) = buf_len;
>
> rxdesc = dmaengine_prep_slave_sg(chan_rx, &dma->sg, 1, DMA_DEV_TO_MEM,
> DMA_PREP_INTERRUPT | DMA_CTRL_ACK);
> @@ -394,6 +412,7 @@ static int at91_do_twi_transfer(struct at91_twi_dev *dev)
> int ret;
> unsigned long time_left;
> bool has_unre_flag = dev->pdata->has_unre_flag;
> + bool has_alt_cmd = dev->pdata->has_alt_cmd;
>
> /*
> * WARNING: the TXCOMP bit in the Status Register is NOT a clear on
> @@ -403,6 +422,21 @@ static int at91_do_twi_transfer(struct at91_twi_dev *dev)
> * empty and STOP condition has been sent.
> * Consequently, we should enable NACK interrupt rather than TXCOMP to
> * detect transmission failure.
> + * Indeed let's take the case of an i2c write command using DMA.
> + * Whenever the slave doesn't acknowledge a byte, the LOCK, NACK and
> + * TXCOMP bits are set together into the Status Register.
> + * LOCK is a clear on write bit, which is set to prevent the DMA
> + * controller from sending new data on the i2c bus after a NACK
> + * condition has happened. Once locked, this i2c peripheral stops
> + * triggering the DMA controller for new data but it is more than
> + * likely that a new DMA transaction is already in progress, writing
> + * into the Transmit Holding Register. Since the peripheral is locked,
> + * these new data won't be sent to the i2c bus but they will remain
> + * into the Transmit Holding Register, so TXCOMP bit is cleared.
> + * Then when the interrupt handler is called, the Status Register is
> + * read: the TXCOMP bit is clear but NACK bit is still set. The driver
> + * manage the error properly, without waiting for timeout.
> + * This case can be reproduced easyly when writing into an at24 eeprom.
> *
> * Besides, the TXCOMP bit is already set before the i2c transaction
> * has been started. For read transactions, this bit is cleared when
> @@ -418,9 +452,9 @@ static int at91_do_twi_transfer(struct at91_twi_dev *dev)
> * condition since we don't know whether the TXCOMP interrupt is enabled
> * before or after the DMA has started to write into THR. So the TXCOMP
> * interrupt is enabled later by at91_twi_write_data_dma_callback().
> - * Immediately after in that DMA callback, we still need to send the
> - * STOP condition manually writing the corresponding bit into the
> - * Control Register.
> + * Immediately after in that DMA callback, if the alternative command
> + * mode is not used, we still need to send the STOP condition manually
> + * writing the corresponding bit into the Control Register.
> */
>
> dev_dbg(dev->dev, "transfer: %s %d bytes.\n",
> @@ -441,14 +475,16 @@ static int at91_do_twi_transfer(struct at91_twi_dev *dev)
> }
>
> /* if only one byte is to be read, immediately stop transfer */
> - if (dev->buf_len <= 1 && !(dev->msg->flags & I2C_M_RECV_LEN))
> + if (!has_alt_cmd && dev->buf_len <= 1 &&
> + !(dev->msg->flags & I2C_M_RECV_LEN))
> start_flags |= AT91_TWI_STOP;
> at91_twi_write(dev, AT91_TWI_CR, start_flags);
> /*
> - * When using dma, the last byte has to be read manually in
> - * order to not send the stop command too late and then
> - * to receive extra data. In practice, there are some issues
> - * if you use the dma to read n-1 bytes because of latency.
> + * When using dma without alternative command mode, the last
> + * byte has to be read manually in order to not send the stop
> + * command too late and then to receive extra data.
> + * In practice, there are some issues if you use the dma to
> + * read n-1 bytes because of latency.
> * Reading n-2 bytes with dma and the two last ones manually
> * seems to be the best solution.
> */
> @@ -477,6 +513,7 @@ static int at91_do_twi_transfer(struct at91_twi_dev *dev)
> time_left = wait_for_completion_timeout(&dev->cmd_complete,
> dev->adapter.timeout);
> if (time_left == 0) {
> + dev->transfer_status |= at91_twi_read(dev, AT91_TWI_SR);
> dev_err(dev->dev, "controller timed out\n");
> at91_init_twi_bus(dev);
> ret = -ETIMEDOUT;
> @@ -497,6 +534,11 @@ static int at91_do_twi_transfer(struct at91_twi_dev *dev)
> ret = -EIO;
> goto error;
> }
> + if (has_alt_cmd && (dev->transfer_status & AT91_TWI_LOCK)) {
> + dev_err(dev->dev, "tx locked\n");
> + ret = -EIO;
> + goto error;
> + }
> if (dev->recv_len_abort) {
> dev_err(dev->dev, "invalid smbus block length recvd\n");
> ret = -EPROTO;
> @@ -508,7 +550,14 @@ static int at91_do_twi_transfer(struct at91_twi_dev *dev)
> return 0;
>
> error:
> + /* first stop DMA transfer if still in progress */
> at91_twi_dma_cleanup(dev);
> + /* then flush THR/FIFO and unlock TX if locked */
> + if (has_alt_cmd && (dev->transfer_status & AT91_TWI_LOCK)) {
> + dev_dbg(dev->dev, "unlock tx\n");
> + at91_twi_write(dev, AT91_TWI_CR,
> + AT91_TWI_THRCLR | AT91_TWI_LOCKCLR);
> + }
> return ret;
> }
>
> @@ -518,6 +567,7 @@ static int at91_twi_xfer(struct i2c_adapter *adap, struct i2c_msg *msg, int num)
> int ret;
> unsigned int_addr_flag = 0;
> struct i2c_msg *m_start = msg;
> + bool is_read, use_alt_cmd = false;
>
> dev_dbg(&adap->dev, "at91_xfer: processing %d messages:\n", num);
>
> @@ -540,8 +590,23 @@ static int at91_twi_xfer(struct i2c_adapter *adap, struct i2c_msg *msg, int num)
> at91_twi_write(dev, AT91_TWI_IADR, internal_address);
> }
>
> - at91_twi_write(dev, AT91_TWI_MMR, (m_start->addr << 16) | int_addr_flag
> - | ((m_start->flags & I2C_M_RD) ? AT91_TWI_MREAD : 0));
> + is_read = (m_start->flags & I2C_M_RD);
> + if (dev->pdata->has_alt_cmd) {
> + if (m_start->len > 0) {
> + at91_twi_write(dev, AT91_TWI_CR, AT91_TWI_ACMEN);
> + at91_twi_write(dev, AT91_TWI_ACR,
> + AT91_TWI_ACR_DATAL(m_start->len) |
> + ((is_read) ? AT91_TWI_ACR_DIR : 0));
> + use_alt_cmd = true;
> + } else {
> + at91_twi_write(dev, AT91_TWI_CR, AT91_TWI_ACMDIS);
> + }
> + }
> +
> + at91_twi_write(dev, AT91_TWI_MMR,
> + (m_start->addr << 16) |
> + int_addr_flag |
> + ((!use_alt_cmd && is_read) ? AT91_TWI_MREAD : 0));
>
> dev->buf_len = m_start->len;
> dev->buf = m_start->buf;
> @@ -582,30 +647,35 @@ static struct at91_twi_pdata at91rm9200_config = {
> .clk_max_div = 5,
> .clk_offset = 3,
> .has_unre_flag = true,
> + .has_alt_cmd = false,
> };
>
> static struct at91_twi_pdata at91sam9261_config = {
> .clk_max_div = 5,
> .clk_offset = 4,
> .has_unre_flag = false,
> + .has_alt_cmd = false,
> };
>
> static struct at91_twi_pdata at91sam9260_config = {
> .clk_max_div = 7,
> .clk_offset = 4,
> .has_unre_flag = false,
> + .has_alt_cmd = false,
> };
>
> static struct at91_twi_pdata at91sam9g20_config = {
> .clk_max_div = 7,
> .clk_offset = 4,
> .has_unre_flag = false,
> + .has_alt_cmd = false,
> };
>
> static struct at91_twi_pdata at91sam9g10_config = {
> .clk_max_div = 7,
> .clk_offset = 4,
> .has_unre_flag = false,
> + .has_alt_cmd = false,
> };
>
> static const struct platform_device_id at91_twi_devtypes[] = {
> @@ -634,6 +704,14 @@ static struct at91_twi_pdata at91sam9x5_config = {
> .clk_max_div = 7,
> .clk_offset = 4,
> .has_unre_flag = false,
> + .has_alt_cmd = false,
> +};
> +
> +static struct at91_twi_pdata at91sama5d2_config = {

No, please name it:

"sama5d2_config"

> + .clk_max_div = 7,
> + .clk_offset = 4,
> + .has_unre_flag = true,
> + .has_alt_cmd = true,
> };
>
> static const struct of_device_id atmel_twi_dt_ids[] = {
> @@ -656,6 +734,9 @@ static const struct of_device_id atmel_twi_dt_ids[] = {
> .compatible = "atmel,at91sam9x5-i2c",
> .data = &at91sam9x5_config,
> }, {
> + .compatible = "atmel,at91sama5d2-i2c",
> + .data = &at91sama5d2_config,

Please remove the "at91" for these products and use "atmel,sama5d2-i2c"

Thanks.

> + }, {
> /* sentinel */
> }
> };
>

--
Nicolas Ferre