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

[Greg KH <gregkh@linuxfoundation.org>]

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@gmail.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@suse.de>
> + * Copyright (C) 2015 Dave Penkler <dpenkler@gmail.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?

thanks,

greg k-h