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

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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




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