linux-kernel - Re: [PATCH 03/16] tty: serial: 8250_core: read only RX if there is something in the FIFO

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Message-ID: <20150212192333.GA18882@linutronix.de>
Date:	Thu, 12 Feb 2015 20:23:33 +0100
From:	Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To:	Peter Hurley <peter@...leysoftware.com>
Cc:	Tony Lindgren <tony@...mide.com>,
	Nicolas Schichan <nschichan@...ebox.fr>,
	gregkh@...uxfoundation.org, linux-serial@...r.kernel.org,
	linux-kernel@...r.kernel.org, balbi@...com,
	linux-omap@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH 03/16] tty: serial: 8250_core: read only RX if there is
 something in the FIFO

* Peter Hurley | 2015-02-12 11:32:04 [-0500]:

>That said, I don't think serial8250_do_startup() is really doing that much
>for OMAP h/w startup; open-coding what omap_8250 really needs is probably
>< 10 loc.

10 loc? I have a few more. serial8250_clear_fifos(),
serial_link_irq_chain() aren't exported. serial8250_set_mctrl() can
maybe accessed via uart_ops->set_mctrl(). Maybe I'm not removing the
obvious not required code but here it looks better to just a BUG flag for
the Omap.

--- a/drivers/tty/serial/8250/8250_omap.c
+++ b/drivers/tty/serial/8250/8250_omap.c
@@ -557,9 +557,74 @@ static int omap_8250_startup(struct uart_port *port)
 
 	pm_runtime_get_sync(port->dev);
 
-	ret = serial8250_do_startup(port);
-	if (ret)
-		goto err;
+	up->mcr = 0;
+
+	/*
+	 * Clear the FIFO buffers and disable them.
+	 * (they will be reenabled in set_termios())
+	 */
+	serial8250_clear_fifos(up);
+
+	/*
+	 * Clear the interrupt registers.
+	 */
+	if (serial_port_in(port, UART_LSR) & UART_LSR_DR)
+		serial_port_in(port, UART_RX);
+	serial_port_in(port, UART_IIR);
+	serial_port_in(port, UART_MSR);
+
+	retval = serial_link_irq_chain(up);
+	if (retval)
+		goto out;
+
+	/*
+	 * Now, initialize the UART
+	 */
+	serial_port_out(port, UART_LCR, UART_LCR_WLEN8);
+
+	spin_lock_irqsave(&port->lock, flags);
+	/*
+	 * Most PC uarts need OUT2 raised to enable interrupts.
+	 */
+	if (port->irq)
+		up->port.mctrl |= TIOCM_OUT2;
+
+	serial8250_set_mctrl(port, port->mctrl);
+
+	spin_unlock_irqrestore(&port->lock, flags);
+
+	/*
+	 * Clear the interrupt registers again for luck, and clear the
+	 * saved flags to avoid getting false values from polling
+	 * routines or the previous session.
+	 */
+	if (serial_port_in(port, UART_LSR) & UART_LSR_DR)
+		serial_port_in(port, UART_RX);
+	serial_port_in(port, UART_IIR);
+	serial_port_in(port, UART_MSR);
+	up->lsr_saved_flags = 0;
+	up->msr_saved_flags = 0;
+
+	/*
+	 * Request DMA channels for both RX and TX.
+	 */
+	if (up->dma) {
+		retval = serial8250_request_dma(up);
+		if (retval) {
+			pr_warn_ratelimited("ttyS%d - failed to request DMA\n",
+					    serial_index(port));
+			up->dma = NULL;
+		}
+	}
+
+	/*
+	 * Finally, enable interrupts.  Note: Modem status interrupts
+	 * are set via set_termios(), which will be occurring imminently
+	 * anyway, so we don't enable them here.
+	 */
+	up->ier = UART_IER_RLSI | UART_IER_RDI;
+	serial_port_out(port, UART_IER, up->ier);
+
 
 #ifdef CONFIG_PM
 	up->capabilities |= UART_CAP_RPM;

Sebastian
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