[PATCH 03/16] tty: serial: 8250_core: read only RX if there is something in the FIFO
From: Peter Hurley <hidden>
Date: 2015-02-12 19:55:44
Also in:
linux-omap, linux-serial, lkml
On 02/12/2015 02:23 PM, Sebastian Andrzej Siewior wrote:
* Peter Hurley | 2015-02-12 11:32:04 [-0500]:quoted
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.
Ok. FWIW,
quoted hunk ↗ jump to hunk
--- 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);
For omap this would just be: serial_out(up, UART_FCR, UART_FCR_CLEAR_RCVR | UART_FCR_CLEAR_XMIT); In any event, the fifo enable/disable is probably not happening since FIFO_EN is ignored unless the divisor == 0.
+ + /* + * 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;
omap doesn't really need the legacy irq chain handling; this could just be request_irq(). In the 8250 split I'll be posting soon, all the irq chaining and polling-via-timeout workarounds stays in the universal/legacy driver so other 8250 drivers can opt-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); +
None of this is required because there is no OUT2 on omap. ---------
--- >% ----+ /* + * 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);
None of this is required because none of the probing is taking place. ------------
+ 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