Re: [PATCH v5 1/5] Implement an ioctl to support the USMTMC-USB488 READ_STATUS_BYTE operation.

Andy Shevchenko
2015-11-22T10:32:44Z

On Sun, Nov 22, 2015 at 11:19 AM, Dave Penkler <dpenkler@gmail.com> wrote:
> On Wed, Nov 18, 2015 at 11:55:27AM +0200, Andy Shevchenko wrote:
>> On Wed, Nov 18, 2015 at 10:37 AM, Dave Penkler <dpenkler@gmail.com> wrote:

>> > + switch (status) {
>> > + case 0: /* SUCCESS */
>> > + if (data->iin_buffer[0] & 0x80) {
>> > + /* check for valid STB notification */
>> > + if ((data->iin_buffer[0] & 0x7f) > 1) {
>>
>> Despite your answer to my comment code is quite understandable even with & 0x7e.
>> You already put comment line about this, you may add that you validate
>> the value to be 127 >= value >= 2.
>>
>
> Yes it is quite understandable but it is less clear. I repeat my comment here:
> When reading the spec and the code it is more obvious that here
> we are testing for the value in bits D6..D0 to be a valid iin_bTag return.
> (See Table 7 in the USBTMC-USB488 spec.)
>
> What is your motivation for
>
> if (data->iin_buffer[0] & 0x7e)
>
> ?

In non-optimized variant it will certainly generate less code. You may
have check assembly code with -O2 and compare. I don't know if
compiler is clever enough to do the same by itself.

>> > + /* urb terminated, clean up */
>> > + dev_dbg(&data->intf->dev,
>> > + "%s - urb terminated, status: %d\n",
>> > + __func__, status);
>>
>> No need to print function here explicitly. Check Dynamic Debug framework.
>
> I am not using dynamic debug but when I enable static debug I get:
>
> [ 1438.562458] usbtmc 1-1:1.0: Enter ioctl_read_stb iin_ep_present: 1
>
> on the console log for
>
> dev_dbg(dev, "Enter ioctl_read_stb iin_ep_present: %d\n",
> data->iin_ep_present);
>
> So if I don't print the function it does not appear on the log.

Whatever maintainers prefer, though I think there are quite rare cases
in USB when someone needs static debug. I'm pretty sure most of the
developers all in favour of dynamic debug.

>> > retcode = sysfs_create_group(&intf->dev.kobj, &data_attr_grp);
>> >
>> > retcode = usb_register_dev(intf, &usbtmc_class);
>>
>> Hmm??? Unrelated to this patch, but notice that retcode is overridden here.

--
With Best Regards,
Andy Shevchenko