Re: [PATCH 34/35] tty: make tty_get_byte_size available

[Jiri Slaby]

On 06. 05. 21, 9:16, Joe Perches wrote:
> On Wed, 2021-05-05 at 11:19 +0200, Jiri Slaby wrote:
> > Many tty drivers contain code to compute bits count depending on termios
> > cflags. So extract this code from serial core to a separate tty helper
> > function called tty_get_byte_size.
> []
> > diff --git a/drivers/tty/tty_ioctl.c b/drivers/tty/tty_ioctl.c
> []
> > +/**
> > + *	tty_get_byte_size	-	get size of a byte
> > + *	@cflag: termios cflag value
> > + *	@account_flags: account for start and stop bits, second stop bit (if
> > + *			set), and parity (if set)
> > + *
> > + *	Get the size of a byte in bits depending on @cflag. Depending on
> > + *	@account_flags parameter, the result also accounts start and stop bits,
> > + *	the second stop bit, and parity bit.
> > + */
> > +unsigned char tty_get_byte_size(unsigned int cflag, bool account_flags)
> > +{
> > +	unsigned char bits = account_flags ? 2 : 0;
> > +
> > +	/* byte size and parity */
> > +	switch (cflag & CSIZE) {
> > +	case CS5:
> > +		bits += 5;
> > +		break;
> > +	case CS6:
> > +		bits += 6;
> > +		break;
> > +	case CS7:
> > +		bits += 7;
> > +		break;
> > +	case CS8:
> > +	default:
> > +		bits += 8;
> > +		break;
> > +	}
> > +
> > +	if (account_flags && (cflag & CSTOPB))
> > +		bits++;
> > +
> > +	if (account_flags && (cflag & PARENB))
> > +		bits++;
> > +
> > +	return bits;
> > +}
> > +EXPORT_SYMBOL_GPL(tty_get_byte_size);
>
> Perhaps clearer not testing account_flags multiple times.

Right. Originally, I had account_start_stop, account_stop, and 
account_parity parameters. But they were either all false or all true. 
So I unified them to account_flags, but the code remained overly complex.

> unsigned char tty_get_byte_size(unsigned int cflag, bool account_flags)
> {
> 	unsigned char bits;
>
> 	/* byte size and parity */
> 	switch (cflag & CSIZE) {
> 	case CS5:
> 		bits = 5;
> 		break;
> 	case CS6:
> 		bits = 6;
> 		break;
> 	case CS7:
> 		bits = 7;
> 		break;
> 	case CS8:
> 	default:
> 		bits = 8;
> 		break;
> 	}
>
> 	if (account_flags) {
> 		bits += 2;	/* start/stop bits */
>
> 		if (cflag & CSTOPB)
> 			bits++;
>
> 		if (cflag & PARENB)
> 			bits++;
> 	}
>
> 	return bits;
> }

thanks,
--
js
suse labs