Re: [PATCHv5 3/3] i2c: altera: Add Altera I2C Controller driver
From: Thor Thayer
Date: Mon Jul 31 2017 - 15:37:42 EST
Hi Wolfram,
Thank you for reviewing.
On 07/31/2017 08:31 AM, Wolfram Sang wrote:
Hi Thor,
thanks for the patches! A few comments and questions from me.
On Mon, Jul 17, 2017 at 11:35:14AM -0500, thor.thayer@xxxxxxxxxxxxxxx wrote:
From: Thor Thayer <thor.thayer@xxxxxxxxxxxxxxx>
Add driver support for the Altera I2C Controller. The I2C
controller is soft IP for use in FPGAs.
Signed-off-by: Thor Thayer <thor.thayer@xxxxxxxxxxxxxxx>
---
v2 Remove altr, from fifo-size to agree with bindings.
Change compatible string to "altr,softip-i2c"
v3 Add version to compatible string "altr,softip-i2c-v1.0"
v4 Add default 100kHz message. Cleanup IRQ error message.
v5 Cleanup header usage - remove init.h.
Fix 1 byte RX bug and add convenience function for transfer shared by RX and TX.
Use readl_poll_timeout_atomic() function.
Cache the I2C Interrupt Status Enable Register.
Cleanup of irq_mask by combining into 1 function.
Use i2c_8bit_addr_from_msg() for cleaner xfer_msg implementation.
Restructure altr_i2c_xfer() without arrays and indexes.
Remove redundant assignments.
Remove function calls from inside if() statements.
Convert of_property_read_u32() to device_property_read_u32().
Call i2c_m_read() once in irq.
---
drivers/i2c/busses/Kconfig | 10 +
drivers/i2c/busses/Makefile | 1 +
drivers/i2c/busses/i2c-altera.c | 510 ++++++++++++++++++++++++++++++++++++++++
3 files changed, 521 insertions(+)
<snip>
new file mode 100644
index 0000000..e818901
--- /dev/null
+++ b/drivers/i2c/busses/i2c-altera.c
@@ -0,0 +1,510 @@
<snip>
+
+#define ALTR_I2C_THRESHOLD 0 /* IRQ Threshold at 1 element */
+#define ALTR_I2C_DFLT_FIFO_SZ 4
+#define ALTR_I2C_TIMEOUT 100000 /* 100ms */
+#define ALTR_I2C_XFER_TIMEOUT (msecs_to_jiffies(250))
+
+/**
+ * altr_i2c_dev - I2C device context
+ * @base: pointer to register struct
+ * @msg: pointer to current message
+ * @msg_len: number of bytes transferred in msg
+ * @msg_err: error code for completed message
+ * @msg_complete: xfer completion object
+ * @dev: device reference
+ * @adapter: core i2c abstraction
+ * @i2c_clk: clock reference for i2c input clock
+ * @bus_clk_rate: current i2c bus clock rate
+ * @buf: ptr to msg buffer for easier use.
+ * @fifo_size: size of the FIFO passed in.
+ */
+struct altr_i2c_dev {
+ void __iomem *base;
+ struct i2c_msg *msg;
+ size_t msg_len;
+ int msg_err;
+ struct completion msg_complete;
+ struct device *dev;
+ struct i2c_adapter adapter;
+ struct clk *i2c_clk;
+ u32 bus_clk_rate;
+ u8 *buf;
+ u32 fifo_size;
+ u32 isr_mask;
The last one is not described in the kernel docs.
Whoops. Yes, I will add this.
+};
+
+static void i2c_int_enable(struct altr_i2c_dev *idev, u32 mask, bool enable)
+{
+ u32 int_en = readl(idev->base + ALTR_I2C_ISER);
+
+ if (enable)
+ idev->isr_mask = int_en | mask;
+ else
+ idev->isr_mask = int_en & ~mask;
+
+ writel(idev->isr_mask, idev->base + ALTR_I2C_ISER);
+}
+
+static void i2c_int_clear(struct altr_i2c_dev *idev, u32 mask)
+{
+ u32 int_en = readl(idev->base + ALTR_I2C_ISR);
+
+ writel(int_en | mask, idev->base + ALTR_I2C_ISR);
+}
Those two functions would also suit an altr_ prefix.
Yes. I will fix this.
+
+static void altr_i2c_core_disable(struct altr_i2c_dev *idev)
+{
+ u32 tmp = readl(idev->base + ALTR_I2C_CTRL);
+
+ writel(tmp & ~ALTR_I2C_CTRL_EN, idev->base + ALTR_I2C_CTRL);
+}
+
+static void altr_i2c_core_enable(struct altr_i2c_dev *idev)
+{
+ u32 tmp = readl(idev->base + ALTR_I2C_CTRL);
+
+ writel(tmp | ALTR_I2C_CTRL_EN, idev->base + ALTR_I2C_CTRL);
+}
+
+static void altr_i2c_reset(struct altr_i2c_dev *idev)
+{
+ altr_i2c_core_disable(idev);
+ altr_i2c_core_enable(idev);
+}
+
+static void altr_i2c_recover(struct altr_i2c_dev *idev)
+{
+ altr_i2c_reset(idev);
+ /* Clock start bit + 8 bits + stop bit out */
Really 8? It should be 9 (ACK bit).
Yes, I'll update the comment.
+ writel(ALTR_I2C_TFR_CMD_STA | ALTR_I2C_TFR_CMD_STO,
+ idev->base + ALTR_I2C_TFR_CMD);
+ altr_i2c_reset(idev);
Why the second reset?
I wanted to start from a known clean condition. The first reset would
reset the hardware. The 2nd would ensure the hardware is ready after
clearing the bus. Maybe I'm being overly cautious but I don't have a way
to check the status of the SDA line.
+
+ i2c_recover_bus(&idev->adapter);
This will return an error since you don't have a struct
i2c_bus_recovery_info defined. This whole recovery looks fishy, maybe it
should be dropped now and added incrementally?
Yes. I'll drop it for now. Thanks.
+}
+
+static inline void altr_i2c_stop(struct altr_i2c_dev *idev)
+{
+ writel(ALTR_I2C_TFR_CMD_STO, idev->base + ALTR_I2C_TFR_CMD);
+}
+
+static void altr_i2c_init(struct altr_i2c_dev *idev)
+{
+ u32 divisor = clk_get_rate(idev->i2c_clk) / idev->bus_clk_rate;
+ u32 clk_mhz = clk_get_rate(idev->i2c_clk) / 1000000;
+ u32 tmp = (ALTR_I2C_THRESHOLD << ALTR_I2C_CTRL_RXT_SHFT) |
+ (ALTR_I2C_THRESHOLD << ALTR_I2C_CTRL_TCT_SHFT);
+ u32 t_high, t_low;
+
+ if (idev->bus_clk_rate <= 100000) {
+ tmp &= ~ALTR_I2C_CTRL_BSPEED;
+ /* Standard mode SCL 50/50 */
+ t_high = divisor * 1 / 2;
+ t_low = divisor * 1 / 2;
+ } else {
+ tmp |= ALTR_I2C_CTRL_BSPEED;
+ /* Fast mode SCL 33/66 */
+ t_high = divisor * 1 / 3;
+ t_low = divisor * 2 / 3;
+ }
+ writel(tmp, idev->base + ALTR_I2C_CTRL);
+
+ dev_dbg(idev->dev, "rate=%uHz per_clk=%uMHz -> ratio=1:%u\n",
+ idev->bus_clk_rate, clk_mhz, divisor);
+
+ /* Reset controller */
+ altr_i2c_reset(idev);
+
+ /* SCL High Time */
+ writel(t_high, idev->base + ALTR_I2C_SCL_HIGH);
+ /* SCL Low Time */
+ writel(t_low, idev->base + ALTR_I2C_SCL_LOW);
+ /* SDA Hold Time, 300ns */
+ writel(div_u64(300 * clk_mhz, 1000), idev->base + ALTR_I2C_SDA_HOLD);
+
+ /* Mask all master interrupt bits */
+ i2c_int_enable(idev, ALTR_I2C_ALL_IRQ, false);
+}
+
+static int i2c_m_rd(const struct i2c_msg *msg)
+{
+ return (msg->flags & I2C_M_RD) != 0;
+}
I'll leave it to you, but I'd think an extra function doesn't really
improve readability here.
OK. I'd seen others using it elsewhere and wanted to stay with
convention but I'll just handle it directly. Thanks.
+
+/**
+ * altr_i2c_transfer - On the last byte to be transmitted, send
+ * a Stop bit on the last byte.
+ */
+static void altr_i2c_transfer(struct altr_i2c_dev *idev, u32 data)
+{
+ /* On the last byte to be transmitted, send STOP */
+ if (idev->msg_len == 1)
+ data |= ALTR_I2C_TFR_CMD_STO;
+ if (idev->msg_len > 0)
+ writel(data, idev->base + ALTR_I2C_TFR_CMD);
+}
+
+/**
+ * altr_i2c_empty_rx_fifo - Fetch data from RX FIFO until end of
+ * transfer. Send a Stop bit on the last byte.
+ */
+static void altr_i2c_empty_rx_fifo(struct altr_i2c_dev *idev)
+{
+ size_t rx_fifo_avail = readl(idev->base + ALTR_I2C_RX_FIFO_LVL);
+ int bytes_to_transfer = min(rx_fifo_avail, idev->msg_len);
+
+ while (bytes_to_transfer-- > 0) {
+ *idev->buf++ = readl(idev->base + ALTR_I2C_RX_DATA);
+ idev->msg_len--;
+ altr_i2c_transfer(idev, 0);
+ }
+}
+
+/**
+ * altr_i2c_fill_tx_fifo - Fill TX FIFO from current message buffer.
+ * @return: Number of bytes left to transfer.
+ */
+static int altr_i2c_fill_tx_fifo(struct altr_i2c_dev *idev)
+{
+ size_t tx_fifo_avail = idev->fifo_size - readl(idev->base +
+ ALTR_I2C_TC_FIFO_LVL);
+ int bytes_to_transfer = min(tx_fifo_avail, idev->msg_len);
+ int ret = idev->msg_len - bytes_to_transfer;
+
+ while (bytes_to_transfer-- > 0) {
+ altr_i2c_transfer(idev, *idev->buf++);
+ idev->msg_len--;
+ }
+
+ return ret;
+}
+
+static irqreturn_t altr_i2c_isr(int irq, void *_dev)
+{
+ int ret, read;
+ struct altr_i2c_dev *idev = _dev;
+ /* Read IRQ status but only interested in Enabled IRQs. */
+ u32 status = readl(idev->base + ALTR_I2C_ISR) & idev->isr_mask;
+
+ if (!idev->msg) {
+ dev_warn(idev->dev, "unexpected interrupt\n");
+ goto out;
Won't you get an interrupt storm if you don't use any i2c_int_clear()?
Yes. I missed that. Thanks.
+ }
+ read = i2c_m_rd(idev->msg);
+
+ /* handle Lost Arbitration */
+ if (unlikely(status & ALTR_I2C_ISR_ARB)) {
+ dev_err(idev->dev, "%s: arbitration lost\n", __func__);
Drop the message, it is not an error, but a to be expected bus condition
in multi-master setups.
OK. Thanks.
+ i2c_int_clear(idev, ALTR_I2C_ISR_ARB);
+ idev->msg_err = -EAGAIN;
+ goto complete;
+ }
+
+ if (unlikely(status & ALTR_I2C_ISR_NACK)) {
+ dev_dbg(idev->dev, "%s: could not get ACK\n", __func__);
+ idev->msg_err = -ENXIO;
+ i2c_int_clear(idev, ALTR_I2C_ISR_NACK);
+ altr_i2c_stop(idev);
+ goto complete;
+ }
+
+ /* handle RX FIFO Overflow */
+ if (read && unlikely(status & ALTR_I2C_ISR_RXOF)) {
+ altr_i2c_empty_rx_fifo(idev);
+ i2c_int_clear(idev, ALTR_I2C_ISR_RXRDY);
+ altr_i2c_stop(idev);
+ dev_err(idev->dev, "%s: RX FIFO Overflow\n", __func__);
+ goto complete;
+ }
+
+ /* RX FIFO needs service? */
+ if (read && (status & ALTR_I2C_ISR_RXRDY)) {
+ altr_i2c_empty_rx_fifo(idev);
+ i2c_int_clear(idev, ALTR_I2C_ISR_RXRDY);
+ if (!idev->msg_len)
+ goto complete;
+
+ goto out;
+ }
+
+ /* TX FIFO needs service? */
+ if (!read && (status & ALTR_I2C_ISR_TXRDY)) {
+ i2c_int_clear(idev, ALTR_I2C_ISR_TXRDY);
+ if (!altr_i2c_fill_tx_fifo(idev))
+ goto complete;
+
+ goto out;
A bit too much goto in here for my taste. What about using a boolean
'complete' variable which gets set or cleared and have an 'if
(complete)' at the end of this routine?
I want to exit immediately on an error - without checking any further
errors or RX or TX. Maybe a switch/case statement would be better.
Yes, the boolean would be cleaner. I will look at better ways to handle
the sequence. Andy's last comment indicated something similar. Thanks.
+ }
+
+complete:
+ /* Wait for the Core to finish */
+ ret = readl_poll_timeout_atomic(idev->base + ALTR_I2C_STATUS, status,
+ ((status & ALTR_I2C_STAT_CORE) == 0),
+ 1, ALTR_I2C_TIMEOUT);
Why do you need this polling in an interrupt?
I wanted to wait for completion before marking it as complete. As you
point out, this isn't appropriate in an interrupt handler. I will look
at this again. Thanks for pointing this out.
+ if (ret)
+ dev_err(idev->dev, "%s: message timeout\n", __func__);
+ i2c_int_enable(idev, ALTR_I2C_ALL_IRQ, false);
+ i2c_int_clear(idev, ALTR_I2C_ALL_IRQ);
+ complete(&idev->msg_complete);
+ dev_dbg(idev->dev, "%s: Message Complete\n", __func__);
+
+out:
+ return IRQ_HANDLED;
+}
+
+static int altr_i2c_xfer_msg(struct altr_i2c_dev *idev, struct i2c_msg *msg)
+{
+ u32 imask = ALTR_I2C_ISR_RXOF | ALTR_I2C_ISR_ARB | ALTR_I2C_ISR_NACK;
+ unsigned long time_left;
+ u32 value;
+ u8 addr = i2c_8bit_addr_from_msg(msg);
+
+ idev->msg = msg;
+ idev->msg_len = msg->len;
+ idev->buf = msg->buf;
+ idev->msg_err = 0;
+ reinit_completion(&idev->msg_complete);
+ altr_i2c_core_enable(idev);
+
+ /* Make sure RX FIFO is empty */
+ do {
+ readl(idev->base + ALTR_I2C_RX_DATA);
+ } while (readl(idev->base + ALTR_I2C_RX_FIFO_LVL));
+
+ writel(ALTR_I2C_TFR_CMD_STA | addr, idev->base + ALTR_I2C_TFR_CMD);
+
+ if (i2c_m_rd(msg)) {
+ imask |= ALTR_I2C_ISER_RXOF_EN | ALTR_I2C_ISER_RXRDY_EN;
+ i2c_int_enable(idev, imask, true);
+ /* write the first byte to start the RX */
+ altr_i2c_transfer(idev, 0);
+ } else {
+ imask |= ALTR_I2C_ISR_TXRDY;
+ i2c_int_enable(idev, imask, true);
+ altr_i2c_fill_tx_fifo(idev);
+ }
+
+ time_left = wait_for_completion_timeout(&idev->msg_complete,
+ ALTR_I2C_XFER_TIMEOUT);
+ i2c_int_enable(idev, imask, false);
+
+ value = readl(idev->base + ALTR_I2C_STATUS) & ALTR_I2C_STAT_CORE;
+ if (value)
+ dev_err(idev->dev, "%s: Core Status not IDLE...\n", __func__);
__func__ with dev_* is 99,9% superfluous.
I will remove this and the other ones above. Andy indicated this as well.
+
+ if (time_left == 0) {
+ idev->msg_err = -ETIMEDOUT;
+ dev_err(idev->dev, "%s: Transaction timed out.\n", __func__);
No error message here. This can happen when an EEPROM is currently
erasing.
OK.
+ altr_i2c_recover(idev);
And no need to reset the bus! Only if SDA is stuck low.
OK. Unfortunately, we can't check the state of the SDA line so I was
being extra cautious. I will remove it.
+ }
+
+ if (unlikely(idev->msg_err) && idev->msg_err != -ENXIO)
+ altr_i2c_init(idev);
Why do you need to reinit on NACK?
OK. Thanks.
+
+ altr_i2c_core_disable(idev);
+
+ return idev->msg_err;
+}
+
+static int
+altr_i2c_xfer(struct i2c_adapter *adap, struct i2c_msg *msgs, int num)
+{
+ struct altr_i2c_dev *idev = i2c_get_adapdata(adap);
+ int i, ret;
+
+ for (i = 0; i < num; i++) {
+ ret = altr_i2c_xfer_msg(idev, msgs++);
+ if (ret)
+ return ret;
+ }
+ return num;
+}
+
+static u32 altr_i2c_func(struct i2c_adapter *adap)
+{
+ return I2C_FUNC_I2C;
+}
No emulated SMBUS?
I was focusing on I2C and wasn't sure about SMBus (particularly the
minimum clock speed). SMBus could be added later but would require some
IP changes.
<snip>