linux-kernel - Re: [EXT] Re: [PATCH RESEND 3/5] USB: serial: cp210x: Added comments to CRTSCT flag code.

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Date:	Tue, 26 Apr 2016 09:26:29 +0200
From:	Johan Hovold <johan@...nel.org>
To:	Konstantin Shkolnyy <Konstantin.Shkolnyy@...abs.com>
Cc:	Johan Hovold <johan@...nel.org>,
	Konstantin Shkolnyy <konstantin.shkolnyy@...il.com>,
	"linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [EXT] Re: [PATCH RESEND 3/5] USB: serial: cp210x: Added comments
 to CRTSCT flag code.

On Mon, Apr 25, 2016 at 06:09:01PM +0000, Konstantin Shkolnyy wrote:
> I was planning to define all these bits in a separate future patch.
> Would you rather prefer the magic numbers defined before fixing the bugs?

Fixing the RTS bug (patch 1), which is the only "real" bug, should be
done before adding defines, and fixing and cleaning up the rest.

> I guess I can do that. Is something like this acceptable?
> 
> /* CP210X_GET_FLOW/CP210X_SET_FLOW read/write these 0x10 bytes */
> struct cp210x_flow_ctl {
> 	u8	SERIAL_DTR_MASK        : 2; /* byte 0 */
> 	u8	                       : 1;
> 	u8	SERIAL_CTS_HANDSHAKE   : 1;
> 	u8	SERIAL_DSR_HANDSHAKE   : 1;
> 	u8	SERIAL_DCD_HANDSHAKE   : 1;
> 	u8	SERIAL_DSR_SENSITIVITY : 1;
> 	u8	                       : 1;
> 	u8; /* byte 1 */
> 	u8; /* byte 2 */
> 	u8; /* byte 3 */
> 	u8	SERIAL_AUTO_TRANSMIT   : 1; /* byte 4 */
> 	u8	SERIAL_AUTO_RECEIVE    : 1;
> 	u8	SERIAL_ERROR_CHAR      : 1;
> 	u8	SERIAL_NULL_STRIPPING  : 1;
> 	u8	SERIAL_BREAK_CHAR      : 1;
> 	u8	                       : 1;
> 	u8	SERIAL_RTS_MASK        : 2;
> 	u8; /* byte 5 */
> 	u8; /* byte 6 */
> 	u8	                       : 7; /* byte 7 */
> 	u8	SERIAL_XOFF_CONTINUE   : 1;
> 	__le32	ulXonLimit;
> 	__le32	ulXoffLimit;
> } __packed;

No, shouldn't rely on the layout of bitfields. Define masks and shifts
as needed and the message structure as

struct cp210x_flow_ctl {
	__le32	ulControlHandshake;
	__le32	ulFlowReplace;
 	__le32	ulXonLimit;
 	__le32	ulXoffLimit;
};

that is, as per AN571.

Thanks,
Johan