Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754476AbaDORkG (ORCPT ); Tue, 15 Apr 2014 13:40:06 -0400 Received: from avon.wwwdotorg.org ([70.85.31.133]:49093 "EHLO avon.wwwdotorg.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753569AbaDORkD (ORCPT ); Tue, 15 Apr 2014 13:40:03 -0400 Message-ID: <534D6EED.8000905@wwwdotorg.org> Date: Tue, 15 Apr 2014 11:39:57 -0600 From: Stephen Warren User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:24.0) Gecko/20100101 Thunderbird/24.2.0 MIME-Version: 1.0 To: Yoshihiro YUNOMAE , Greg Kroah-Hartman , Heikki Krogerus , Stephen Warren , Alan CC: Jingoo Han , linux-kernel@vger.kernel.org, Hidehiro Kawai , linux-serial@vger.kernel.org, yrl.pp-manager.tt@hitachi.com, Masami Hiramatsu , Aaron Sierra , Jiri Slaby Subject: Re: [PATCH V5.1] serial/uart/8250: Add tunable RX interrupt trigger I/F of FIFO buffers References: <20140415055216.14660.18270.stgit@yunodevel> <20140415080649.19209.60645.stgit@yunodevel> In-Reply-To: <20140415080649.19209.60645.stgit@yunodevel> X-Enigmail-Version: 1.5.2 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 04/15/2014 02:06 AM, Yoshihiro YUNOMAE wrote: > /* I found a bug in V5, so I resend this as V5.1. Please do not review V5. */ > > Add tunable RX interrupt trigger I/F of FIFO buffers. > Serial devices are used as not only message communication devices but control > or sending communication devices. For the latter uses, normally small data > will be exchanged, so user applications want to receive data unit as soon as > possible for real-time tendency. If we have a sensor which sends a 1 byte data > each time and must control a device based on the sensor feedback, the RX > interrupt should be triggered for each data. > > According to HW specification of serial UART devices, RX interrupt trigger > can be changed, but the trigger is hard-coded. For example, RX interrupt trigger > in 16550A can be set to 1, 4, 8, or 14 bytes for HW, but current driver sets > the trigger to only 8bytes. > diff --git a/drivers/tty/serial/8250/8250.h b/drivers/tty/serial/8250/8250.h > +#define FCR_RX_TRIG_OFFSET 6 Isn't "SHIFT" the usual term rather than "OFFSET". Why not add this define into include/uapi/linux/serial_reg.h, along with all the other UART_FCR_TRIGGER_* defines? > +#define FCR_RX_TRIG_BITS(x) (((x) >> FCR_RX_TRIG_OFFSET) & 0x3) Perhaps use UART_FCR_TRIGGER_MASK rather than a hard-coded "3" (and then you'd have to mask before shifting). > diff --git a/drivers/tty/serial/8250/8250_core.c b/drivers/tty/serial/8250/8250_core.c > @@ -2275,10 +2276,9 @@ serial8250_do_set_termios(struct uart_port *port, struct ktermios *termios, > if (up->capabilities & UART_CAP_FIFO && port->fifosize > 1) { > - fcr = uart_config[port->type].fcr; > - if ((baud < 2400 && !up->dma) || fifo_bug) { > - fcr &= ~UART_FCR_TRIGGER_MASK; > - fcr |= UART_FCR_TRIGGER_1; > + /* NOTE: If fifo_bug is not set, a uaser can set RX_trigger. */ > + if ((baud < 2400 && !up->dma && > + (up->fcr == uart_config[port->type].fcr)) || up->fifo_bug) { > + up->fcr &= ~UART_FCR_TRIGGER_MASK; > + up->fcr |= UART_FCR_TRIGGER_1; > } > } Does the "(up->fcr == uart_config[port->type].fcr)" term prevent the user from changing the trigger level multiple times? Perhaps this is intended? > +static int convert_fcr2val(struct uart_8250_port *up) "val" is rather generic here, and doesn't describe what the function is doing. What about fcr_get_rxtrig_bytes()? > +{ > + const struct serial8250_config *conf_type = &uart_config[up->port.type]; > + unsigned char rx_trig_raw = up->fcr & UART_FCR_TRIGGER_MASK; > + unsigned char val; > + > + val = conf_type->rx_trig_byte[FCR_RX_TRIG_BITS(rx_trig_raw)]; Given that FCR_RX_TRIG_BITS() does all the required shifting/masking, why not just: val = conf_type->rx_trig_byte[FCR_RX_TRIG_BITS(up->fcr)]; > +static int convert_val2rxtrig(struct uart_8250_port *up, unsigned char val) Perhaps name this bytes_to_fcr_txtrig()? > +static void register_dev_spec_attr_grp(struct uart_8250_port *up) > +{ > + switch (up->port.type) { > + case PORT_16550A: > + case PORT_16650V2: > + case PORT_16654: > + case PORT_16750: > + case PORT_TEGRA: Why not replace that with: const struct serial8250_config *conf_type = &uart_config[up->port.type]; if (conf_type->rx_trig_byte[0]) { (or something like that anyway) That means this switch statement doesn't need to be updated when new UART types are modified to set up the rx_trig_byte field. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/