On Fri, Apr 24, 2015 at 5:49 AM, Ellen Wang <ellen@xxxxxxxxxxxxxxxxxxx> wrote:
> cp2112_i2c_xfer() only supports a single i2c_msg and only
> reads up to 61 bytes. More than one message at a time
> and longers reads just return errors.
>
> This is a serious limitation. For example, the at24 eeprom driver
> generates paired write and read messages (for eeprom address and data).
> And the reads can be quite large. The fix consists of a loop
> to go through all the messages, and a loop around cp2112_read()
> to pick up all the returned data. For extra credit, it now also
> supports write-read pairs and implements them as
> CP2112_DATA_WRITE_READ_REQUEST.
>
> Signed-off-by: Ellen Wang <ellen@xxxxxxxxxxxxxxxxxxx>
Hi Ellen,
the patch is partially wrong. See below.
I added Wolfram, I2C subsystem maintainer, in copy.
> ---
> drivers/hid/hid-cp2112.c | 136 +++++++++++++++++++++++++++++-----------------
> 1 file changed, 87 insertions(+), 49 deletions(-)
>
> diff --git a/drivers/hid/hid-cp2112.c b/drivers/hid/hid-cp2112.c
> index 3318de6..e7e72a4 100644
> --- a/drivers/hid/hid-cp2112.c
> +++ b/drivers/hid/hid-cp2112.c
> @@ -444,11 +444,30 @@ static int cp2112_i2c_write_req(void *buf, u8 slave_address, u8 *data,
> return data_length + 3;
> }
>
> +static int cp2112_i2c_write_read_req(void *buf, u8 slave_address,
> + u8 *addr, int addr_length,
> + int read_length)
> +{
> + struct cp2112_write_read_req_report *report = buf;
> +
> + if (read_length < 1 || read_length > 512 ||
> + addr_length > sizeof(report->target_address))
> + return -EINVAL;
> +
> + report->report = CP2112_DATA_WRITE_READ_REQUEST;
> + report->slave_address = slave_address << 1;
> + report->length = cpu_to_be16(read_length);
> + report->target_address_length = addr_length;
> + memcpy(report->target_address, addr, addr_length);
> + return addr_length + 5;
> +}
> +
> static int cp2112_i2c_xfer(struct i2c_adapter *adap, struct i2c_msg *msgs,
> int num)
> {
> struct cp2112_device *dev = (struct cp2112_device *)adap->algo_data;
> struct hid_device *hdev = dev->hdev;
> + struct i2c_msg *m;
> u8 buf[64];
> ssize_t count;
> unsigned int retries;
> @@ -456,71 +475,90 @@ static int cp2112_i2c_xfer(struct i2c_adapter *adap, struct i2c_msg *msgs,
>
> hid_dbg(hdev, "I2C %d messages\n", num);
>
> - if (num != 1) {
> - hid_err(hdev,
> - "Multi-message I2C transactions not supported\n");
> - return -EOPNOTSUPP;
> - }
> -
> - if (msgs->flags & I2C_M_RD)
> - count = cp2112_read_req(buf, msgs->addr, msgs->len);
> - else
> - count = cp2112_i2c_write_req(buf, msgs->addr, msgs->buf,
> - msgs->len);
> -
> - if (count < 0)
> - return count;
> -
> ret = hid_hw_power(hdev, PM_HINT_FULLON);
> if (ret < 0) {
> hid_err(hdev, "power management error: %d\n", ret);
> return ret;
> }
>
> - ret = cp2112_hid_output(hdev, buf, count, HID_OUTPUT_REPORT);
> - if (ret < 0) {
> - hid_warn(hdev, "Error starting transaction: %d\n", ret);
> - goto power_normal;
> - }
> + for (m = msgs; m < msgs + num; m++) {
CP2112 is not able to combine messages since unable to repeat the start bits.
It can only send simple transfers or a combined read-after-write.
Here you cannot simply loop on all the messages and send them one by
one because there is no way to force the repeated start bit in
between.
You can find more details in this thread about CP2112
https://lkml.org/lkml/2015/3/15/64
and here info about the repeated start bit under "Combined transactions"
Documentation/i2c/i2c-protocol
Anyway your idea to introduce read-after-write is valid.
I suggest you to check the drivers i2c-opal.c and i2c-pmcmsp.c ; at a
quick check I think they have similar limitation as CP2112.
You could replicate the same check, supporting only num==1 (always)
and num==2 (only if msg[0] is write and msg[1] is read).
Best Regards,
Antonio
> + /*
> + * If the top two messages are a write followed by a read,
> + * then we do them together as CP2112_DATA_WRITE_READ_REQUEST.
> + * Otherwise, process one message.
> + */
> +
> + if (m + 1 < msgs + num && m[0].addr == m[1].addr &&
> + !(m[0].flags & I2C_M_RD) && (m[1].flags & I2C_M_RD)) {
> + hid_dbg(hdev, "I2C msg %zd write-read %#04x wlen %d rlen %d\n",
> + m - msgs, m[0].addr, m[0].len, m[1].len);
> + count = cp2112_i2c_write_read_req(buf, m[0].addr,
> + m[0].buf, m[0].len, m[1].len);
> + m++;
> + } else if (m->flags & I2C_M_RD) {
> + hid_dbg(hdev, "I2C msg %zd read %#04x len %d\n",
> + m - msgs, m->addr, m->len);
> + count = cp2112_read_req(buf, m->addr, m->len);
> + } else {
> + hid_dbg(hdev, "I2C msg %zd write %#04x len %d\n",
> + m - msgs, m->addr, m->len);
> + count = cp2112_i2c_write_req(buf, m->addr, m->buf,
> + m->len);
> + }
>
> - for (retries = 0; retries < XFER_STATUS_RETRIES; ++retries) {
> - ret = cp2112_xfer_status(dev);
> - if (-EBUSY == ret)
> - continue;
> - if (ret < 0)
> + if (count < 0) {
> + ret = count;
> goto power_normal;
> - break;
> - }
> + }
>
> - if (XFER_STATUS_RETRIES <= retries) {
> - hid_warn(hdev, "Transfer timed out, cancelling.\n");
> - buf[0] = CP2112_CANCEL_TRANSFER;
> - buf[1] = 0x01;
> + ret = cp2112_hid_output(hdev, buf, count, HID_OUTPUT_REPORT);
> + if (ret < 0) {
> + hid_warn(hdev, "Error starting transaction: %d\n", ret);
> + goto power_normal;
> + }
>
> - ret = cp2112_hid_output(hdev, buf, 2, HID_OUTPUT_REPORT);
> - if (ret < 0)
> - hid_warn(hdev, "Error cancelling transaction: %d\n",
> - ret);
> + for (retries = 0; retries < XFER_STATUS_RETRIES; ++retries) {
> + ret = cp2112_xfer_status(dev);
> + if (-EBUSY == ret)
> + continue;
> + if (ret < 0)
> + goto power_normal;
> + break;
> + }
>
> - ret = -ETIMEDOUT;
> - goto power_normal;
> - }
> + if (XFER_STATUS_RETRIES <= retries) {
> + hid_warn(hdev, "Transfer timed out, cancelling.\n");
> + buf[0] = CP2112_CANCEL_TRANSFER;
> + buf[1] = 0x01;
>
> - if (!(msgs->flags & I2C_M_RD))
> - goto finish;
> + ret = cp2112_hid_output(hdev, buf, 2,
> + HID_OUTPUT_REPORT);
> + if (ret < 0)
> + hid_warn(hdev,
> + "Error cancelling transaction: %d\n",
> + ret);
>
> - ret = cp2112_read(dev, msgs->buf, msgs->len);
> - if (ret < 0)
> - goto power_normal;
> - if (ret != msgs->len) {
> - hid_warn(hdev, "short read: %d < %d\n", ret, msgs->len);
> - ret = -EIO;
> - goto power_normal;
> + ret = -ETIMEDOUT;
> + goto power_normal;
> + }
> +
> + if (!(m->flags & I2C_M_RD))
> + continue;
> +
> + for (count = 0; count < m->len;) {
> + ret = cp2112_read(dev, m->buf + count, m->len - count);
> + if (ret < 0)
> + goto power_normal;
> + count += ret;
> + if (count > m->len) {
> + hid_warn(hdev, "long read: %d > %zd\n",
> + ret, m->len - count + ret);
> + }
> + }
> }
>
> -finish:
> /* return the number of transferred messages */
> - ret = 1;
> + ret = num;
>
> power_normal:
> hid_hw_power(hdev, PM_HINT_NORMAL);
> --
> 1.7.10.4
>
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