linux-kernel - Re: [PATCH 34/35] tty: make tty_get_byte

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Date:   Thu, 06 May 2021 00:16:08 -0700
From:   Joe Perches <joe@...ches.com>
To:     Jiri Slaby <jslaby@...e.cz>, gregkh@...uxfoundation.org
Cc:     linux-serial@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 34/35] tty: make tty_get_byte_size available

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.

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;
}