From mboxrd@z Thu Jan 1 00:00:00 1970 From: Ellen Wang Subject: Re: [PATCH v2] HID: cp2112: support large i2c transfers in hid-cp2112 Date: Wed, 08 Jul 2015 11:08:56 -0700 Message-ID: <559D6738.1050003@cumulusnetworks.com> References: <1436351118-3360-1-git-send-email-ellen@cumulusnetworks.com> <559D126B.6050505@linaro.org> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <559D126B.6050505-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org> Sender: linux-i2c-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Vaibhav Hiremath , borneo.antonio-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org, dbarksdale-2SNLKkHU5xRBDgjK7y7TUQ@public.gmane.org, jkosina-AlSwsSmVLrQ@public.gmane.org, linux-input-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-i2c-u79uwXL29TY76Z2rM5mHXA@public.gmane.org List-Id: linux-i2c@vger.kernel.org On 07/08/2015 05:07 AM, Vaibhav Hiremath wrote: > > > 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 >> --- >> 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 ? Yeah. Sorry. I had debugging code in my workspace then ran git diff with the wrong options. I'll resend. >> + 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? (count > msgs->len) should never happen, so there's really no predicting it. Or do you mean something else? > Thanks, > Vaibhav Thank you.