linux-kernel - Re: [PATCH v6 4/5] Add ioctl to retrieve USBTMC-USB488 capabilities

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Date:	Tue, 26 Jan 2016 19:15:23 +0100
From:	Dave Penkler <dpenkler@...il.com>
To:	Greg KH <gregkh@...uxfoundation.org>
Cc:	peter.chen@...escale.com, teuniz@...il.com,
	linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v6 4/5] Add ioctl to retrieve USBTMC-USB488 capabilities

On Sun, Jan 24, 2016 at 08:42:54PM -0800, Greg KH wrote:
> On Sun, Nov 29, 2015 at 01:35:51PM +0100, Dave Penkler wrote:
> > This is a convenience function to obtain an instrument's
> > capabilities from its file descriptor without having to access sysfs
> > from the user program.
> > 
> > Signed-off-by: Dave Penkler <dpenkler@...il.com>
> > ---
> >  drivers/usb/class/usbtmc.c   | 12 ++++++++++++
> >  include/uapi/linux/usb/tmc.h | 21 ++++++++++++++++++---
> >  2 files changed, 30 insertions(+), 3 deletions(-)
> > 
> > diff --git a/drivers/usb/class/usbtmc.c b/drivers/usb/class/usbtmc.c
> > index 3b85ef5..3a3264c 100644
> > --- a/drivers/usb/class/usbtmc.c
> > +++ b/drivers/usb/class/usbtmc.c
> > @@ -102,6 +102,9 @@ struct usbtmc_device_data {
> >  	u16            iin_wMaxPacketSize;
> >  	atomic_t       srq_asserted;
> >  
> > +	/* coalesced usb488_caps from usbtmc_dev_capabilities */
> > +	u8 usb488_caps;
> > +
> >  	u8 rigol_quirk;
> >  
> >  	/* attributes from the USB TMC spec for this device */
> > @@ -992,6 +995,7 @@ static int get_capabilities(struct usbtmc_device_data *data)
> >  	data->capabilities.device_capabilities = buffer[5];
> >  	data->capabilities.usb488_interface_capabilities = buffer[14];
> >  	data->capabilities.usb488_device_capabilities = buffer[15];
> > +	data->usb488_caps = (buffer[14] & 0x07) | ((buffer[15] & 0x0f) << 4);
> >  	rv = 0;
> >  
> >  err_out:
> > @@ -1167,6 +1171,14 @@ static long usbtmc_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
> >  		retval = usbtmc_ioctl_abort_bulk_in(data);
> >  		break;
> >  
> > +	case USBTMC488_IOCTL_GET_CAPS:
> > +		retval = copy_to_user((void __user *)arg,
> > +				&data->usb488_caps,
> > +				sizeof(data->usb488_caps));
> > +		if (retval)
> > +			retval = -EFAULT;
> > +		break;
> > +
> >  	case USBTMC488_IOCTL_READ_STB:
> >  		retval = usbtmc488_ioctl_read_stb(data, arg);
> >  		break;
> > diff --git a/include/uapi/linux/usb/tmc.h b/include/uapi/linux/usb/tmc.h
> > index 7e5ced8..1dc3af1 100644
> > --- a/include/uapi/linux/usb/tmc.h
> > +++ b/include/uapi/linux/usb/tmc.h
> > @@ -2,12 +2,14 @@
> >   * Copyright (C) 2007 Stefan Kopp, Gechingen, Germany
> >   * Copyright (C) 2008 Novell, Inc.
> >   * Copyright (C) 2008 Greg Kroah-Hartman <gregkh@...e.de>
> > + * Copyright (C) 2015 Dave Penkler <dpenkler@...il.com>
> >   *
> >   * This file holds USB constants defined by the USB Device Class
> > - * Definition for Test and Measurement devices published by the USB-IF.
> > + * and USB488 Subclass Definitions for Test and Measurement devices
> > + * published by the USB-IF.
> >   *
> > - * It also has the ioctl definitions for the usbtmc kernel driver that
> > - * userspace needs to know about.
> > + * It also has the ioctl and capability definitions for the
> > + * usbtmc kernel driver that userspace needs to know about.
> >   */
> >  
> >  #ifndef __LINUX_USB_TMC_H
> > @@ -40,6 +42,19 @@
> >  #define USBTMC_IOCTL_ABORT_BULK_IN	_IO(USBTMC_IOC_NR, 4)
> >  #define USBTMC_IOCTL_CLEAR_OUT_HALT	_IO(USBTMC_IOC_NR, 6)
> >  #define USBTMC_IOCTL_CLEAR_IN_HALT	_IO(USBTMC_IOC_NR, 7)
> > +#define USBTMC488_IOCTL_GET_CAPS	_IO(USBTMC_IOC_NR, 17)
> 
> Shouldn't there be a data structure mentioned here that gets passed back
> to userspace?  And are you sure the direction is correct as well?
> 

Oops, it should read:

#define USBTMC488_IOCTL_GET_CAPS   _IOR(USBTMC_IOC_NR, 17, unsigned char)

Thanks,
-dave

> thanks,
> 
> greg k-h