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

[Martyn Welch]

On 14/01/16 17:10, Konstantin Shkolnyy wrote:
> > -----Original Message-----
> > From: linux-usb-owner@xxxxxxxxxxxxxxx [mailto:linux-usb-
> > owner@xxxxxxxxxxxxxxx] On Behalf Of Martyn Welch
> > Sent: Thursday, January 14, 2016 10:31
> > To: Konstantin Shkolnyy; johan@xxxxxxxxxx
> > Cc: linux-usb@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx
> > 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@xxxxxxxxx>
> > > ---
> > >    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.

Ah, gotcha - conversion done in cp210x_read_u16_reg().

Martyn