linux-kernel - RE: [PATCH v2 1/3 RESEND] USB: serial: cp210x: New 16-bit register access functions.

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Date:	Thu, 14 Jan 2016 17:10:00 +0000
From:	Konstantin Shkolnyy <Konstantin.Shkolnyy@...abs.com>
To:	Martyn Welch <martyn.welch@...labora.co.uk>,
	Konstantin Shkolnyy <konstantin.shkolnyy@...il.com>,
	"johan@...nel.org" <johan@...nel.org>
CC:	"linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH v2 1/3 RESEND] USB: serial: cp210x: New 16-bit register
 access functions.

> -----Original Message-----
> From: linux-usb-owner@...r.kernel.org [mailto:linux-usb-
> owner@...r.kernel.org] On Behalf Of Martyn Welch
> Sent: Thursday, January 14, 2016 10:31
> To: Konstantin Shkolnyy; johan@...nel.org
> Cc: linux-usb@...r.kernel.org; linux-kernel@...r.kernel.org
> Subject: Re: [PATCH v2 1/3 RESEND] USB: serial: cp210x: New 16-bit register
> access functions.
> 
> On 23/12/15 02:14, Konstantin Shkolnyy wrote:
> > cp210x_get_config and cp210x_set_config are cumbersome to use. This
> change
> > introduces new register access functions for 16-bit values, instead of
> > the above functions.
> >
> > Signed-off-by: Konstantin Shkolnyy <konstantin.shkolnyy@...il.com>
> > ---
> >   drivers/usb/serial/cp210x.c | 155
> +++++++++++++++++++++++++++++++-------------
> >   1 file changed, 111 insertions(+), 44 deletions(-)
> >
> > diff --git a/drivers/usb/serial/cp210x.c b/drivers/usb/serial/cp210x.c
> > index fd67958..fd7c4f4 100644
> > --- a/drivers/usb/serial/cp210x.c
> > +++ b/drivers/usb/serial/cp210x.c
> > @@ -422,14 +422,88 @@ static int cp210x_set_config(struct
> usb_serial_port *port, u8 request,
> >   }
> >
> >   /*
> > - * cp210x_set_config_single
> > - * Convenience function for calling cp210x_set_config on single data
> values
> > - * without requiring an integer pointer
> > + * Reads a variable-sized block of CP210X_ registers, identified by req.
> > + * Returns data into buf in native USB byte order.
> >    */
> > -static inline int cp210x_set_config_single(struct usb_serial_port *port,
> > -		u8 request, unsigned int data)
> > +static int cp210x_read_reg_block(struct usb_serial_port *port, u8 req,
> > +		void *buf, int bufsize)
> >   {
> > -	return cp210x_set_config(port, request, &data, 2);
> > +	struct usb_serial *serial = port->serial;
> > +	struct cp210x_port_private *port_priv =
> usb_get_serial_port_data(port);
> > +	void *dmabuf;
> > +	int result;
> > +
> > +	dmabuf = kmalloc(bufsize, GFP_KERNEL);
> > +	if (!dmabuf) {
> > +		/*
> > +		 * FIXME Some callers don't bother to check for error,
> > +		 * at least give them consistent junk until they are fixed
> > +		 */
> > +		memset(buf, 0, bufsize);
> > +		return -ENOMEM;
> > +	}
> > +
> > +	result = usb_control_msg(serial->dev, usb_rcvctrlpipe(serial->dev,
> 0),
> > +			req, REQTYPE_INTERFACE_TO_HOST, 0,
> > +			port_priv->bInterfaceNumber, dmabuf, bufsize,
> > +			USB_CTRL_SET_TIMEOUT);
> > +	if (result == bufsize) {
> > +		memcpy(buf, dmabuf, bufsize);
> > +		result = 0;
> 
> I could be wrong, but isn't dmabuf a little-endian stream (hence the
> byte order swapping in the existing set and get functions). Won't this
> break on big endian systems due to the lack of byte swapping?

This function is intended to not convert, as I tried to say in the header comment.