linux-kernel - Re: [PATCH v5 1/5] Implement an ioctl to support the USMTMC-USB488 READ_STATUS

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Message-ID: <20151122091952.GB4581@slacky>
Date:	Sun, 22 Nov 2015 10:19:52 +0100
From:	Dave Penkler <dpenkler@...il.com>
To:	Andy Shevchenko <andy.shevchenko@...il.com>
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	peter.chen@...escale.com, teuniz@...il.com,
	USB <linux-usb@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v5 1/5] Implement an ioctl to support the USMTMC-USB488
 READ_STATUS_BYTE operation.

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@...il.com> wrote:
> > Background:
> > When performing a read on an instrument that is executing a function
> > that runs longer than the USB timeout the instrument may hang and
> > require a device reset to recover. The READ_STATUS_BYTE operation
> > always returns even when the instrument is busy permitting to poll
> > for the appropriate condition. This capability is referred to in
> > instrument application notes on synchronizing acquisitions for other
> > platforms.
> >
> 
> First of all, please be patient and do not send patches immediately
> when you answered to someone's review. It increases redundant noise
> and burden on reviewer. Wait at least for 24h especially if there are
> topics still to discuss.
> 

OK, apologies.

snip

> > +
> > +       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)

?

> > +                               data->bNotify1 = data->iin_buffer[0];
> > +                               data->bNotify2 = data->iin_buffer[1];
> > +                               atomic_set(&data->iin_data_valid, 1);
> > +                               wake_up_interruptible(&data->waitq);
> > +                               goto exit;
> > +                       }
> > +               }

snip

> > +               /* 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.

> 
> > +               return;
> > +       default:
> > +               dev_err(&data->intf->dev,
> > +                       "%s - unknown status received: %d\n",
> > +                       __func__, status);
> > +       }
> > +exit:
> > +       rv = usb_submit_urb(urb, GFP_ATOMIC);
> > +       if (rv) {
> > +               dev_err(&data->intf->dev, "%s - usb_submit_urb failed: %d\n",
> > +                       __func__, rv);
> > +       }
> > +}

snip

> > +
> > +               /* fill interrupt urb */
> > +               usb_fill_int_urb(data->iin_urb, data->usb_dev,
> > +                               usb_rcvintpipe(data->usb_dev, data->iin_ep),
> > +                               data->iin_buffer, data->iin_wMaxPacketSize,
> > +                               usbtmc_interrupt,
> > +                               data, data->iin_interval);
> > +
> > +               if (usb_submit_urb(data->iin_urb, GFP_KERNEL)) {
> 
> Does it return a proper error code?
> 

Yes, will propagate it.

> > +                       retcode = -EIO;
> > +                       dev_err(&intf->dev, "Failed to submit iin_urb\n");
> > +                       goto error_register;
> > +               }
> > +       }
> > +
> 
> >         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.
> 
> 
> > @@ -1185,6 +1395,7 @@ static int usbtmc_probe(struct usb_interface *intf,
> >  error_register:
> >         sysfs_remove_group(&intf->dev.kobj, &capability_attr_grp);
> >         sysfs_remove_group(&intf->dev.kobj, &data_attr_grp);
> > +       usbtmc_free_int(data);
> >         kref_put(&data->kref, usbtmc_delete);
> >         return retcode;
> >  }
> 
> 
> -- 
> With Best Regards,
> Andy Shevchenko
cheers,
-Dave
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