Re: [PATCH v2] HID: cp2112: support large i2c transfers in hid-cp2112

[Vaibhav Hiremath <vaibhav.hiremath-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org>]

On Wednesday 08 July 2015 03:55 PM, Ellen Wang wrote:
> cp2112_i2c_xfer() only reads up to 61 bytes, returning EIO
> on longers reads.  The fix is to wrap a loop around
> cp2112_read() to pick up all the returned data.
>
> Signed-off-by: Ellen Wang <ellen-qUQiAmfTcIp+XZJcv9eMoEEOCMrvLtNR@public.gmane.org>
> ---
> This is the updated patch with a check for 0 return from
> cp2112_read().  I tested it with a suitable delay in the loop
> to trigger the cp2112_raw_event() overrun bug, which must
> be fixed before this patch is applied.
> ---
>   drivers/hid/hid-cp2112.c | 33 ++++++++++++++++++++++++++-------
>   1 file changed, 26 insertions(+), 7 deletions(-)
>
> diff --git a/drivers/hid/hid-cp2112.c b/drivers/hid/hid-cp2112.c
> index 3318de6..e2ffac0 100644
> --- a/drivers/hid/hid-cp2112.c
> +++ b/drivers/hid/hid-cp2112.c
> @@ -509,13 +509,32 @@ static int cp2112_i2c_xfer(struct i2c_adapter *adap, struct i2c_msg *msgs,
>   	if (!(msgs->flags & I2C_M_RD))
>   		goto finish;
>
> -	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;
> +	for (count = 0; count < msgs->len;) {
> +		ret = cp2112_read(dev, msgs->buf + count, msgs->len - count);
> +		hid_warn(hdev, "read returned %d for %zd\n",
> +			 ret, msgs->len - count);

Do you always want to throw warning here, unconditionally ?

> +		if (ret < 0)
> +			goto power_normal;
> +		if (ret == 0) {
> +			hid_err(hdev, "read returned 0\n");
> +			ret = -EIO;
> +			goto power_normal;
> +		}

bit simplified, I guess :)

if (ret < 0 || ret == 0) {
	hid_err(hdev, "read returned %d", ret);
	ret = ret == 0 ? -EIO : ret;
	goto power_normal;
}


> +		count += ret;
> +		if (count > msgs->len) {
> +			/*
> +			 * The hardware returned too much data.
> +			 * This is mostly harmless because cp2112_read()
> +			 * has a limit check so didn't overrun our
> +			 * buffer.  Nevertheless, we return an error
> +			 * because something is seriously wrong and
> +			 * it shouldn't go unnoticed.
> +			 */
> +			hid_err(hdev, "long read: %d > %zd\n",
> +				ret, msgs->len - count + ret);

You may want to take another look here.
'ret' will be either,

	- ret = msgs->len
		Not applicable
	- ret > msgs->len
		(count > msgs->len) will happen in one single
		iteration, and will
	- ret < msgs->len
		(count > msgs->len) will happen in multiple iterations
		where count keeps incrementing based on ret

In the 2 scenarios above, I believe you would want to show,

	actual read bytes > requested read bytes


Am I missing something here?

Thanks,
Vaibhav