RISC-V doesn't support interrupts for the time being, so it would be nice to have polling mode.
The patch adds new option to console='...,polling' which forces driver to use polling mode. If there is no interrupt property in UART node, then polling will be used. According to 4.2.2 National Semiconductor 16450/16550 Compatible UART Requirements from The Devicetree Specification v0.4 ( https://www.devicetree.org/specifications/ ) the interrupt property is optional. Also, it is possible that interrupt '0' can be used for some architectures as an legal UART interrupt number ( according to dts files in Linux kernel ), so the check of the return value of platform_get_irq() was updated in case of when device tree is used for UART initialization. For example: https://github.com/torvalds/linux/blob/master/arch/powerpc/boot/dts/ebony.dts#L197 Signed-off-by: Oleksii Kurochko <oleksii.kuroc...@gmail.com> --- xen/drivers/char/console.c | 2 ++ xen/drivers/char/ns16550.c | 38 ++++++++++++++++++++++++++++---------- 2 files changed, 30 insertions(+), 10 deletions(-) diff --git a/xen/drivers/char/console.c b/xen/drivers/char/console.c index 0e410fa086..07e9610d77 100644 --- a/xen/drivers/char/console.c +++ b/xen/drivers/char/console.c @@ -993,6 +993,8 @@ void __init console_init_preirq(void) #endif else if ( !strncmp(p, "none", 4) ) continue; + else if ( !strncmp(p, "polling", 7 ) + continue; else if ( (sh = serial_parse_handle(p)) >= 0 ) { sercon_handle = sh; diff --git a/xen/drivers/char/ns16550.c b/xen/drivers/char/ns16550.c index 2aed6ec707..a6eb3b3997 100644 --- a/xen/drivers/char/ns16550.c +++ b/xen/drivers/char/ns16550.c @@ -58,7 +58,11 @@ static struct ns16550 { struct timer timer; struct timer resume_timer; unsigned int timeout_ms; - bool_t intr_works; + enum { + intr_off, + intr_on, + polling, + } intr_works; bool_t dw_usr_bsy; #ifdef NS16550_PCI /* PCI card parameters. */ @@ -181,7 +185,7 @@ static void cf_check ns16550_interrupt( struct serial_port *port = dev_id; struct ns16550 *uart = port->uart; - uart->intr_works = 1; + uart->intr_works = intr_on; while ( !(ns_read_reg(uart, UART_IIR) & UART_IIR_NOINT) ) { @@ -212,7 +216,7 @@ static void cf_check __ns16550_poll(struct cpu_user_regs *regs) struct serial_port *port = this_cpu(poll_port); struct ns16550 *uart = port->uart; - if ( uart->intr_works ) + if ( uart->intr_works == intr_on ) return; /* Interrupts work - no more polling */ while ( ns_read_reg(uart, UART_LSR) & UART_LSR_DR ) @@ -305,7 +309,8 @@ static void ns16550_setup_preirq(struct ns16550 *uart) unsigned char lcr; unsigned int divisor; - uart->intr_works = 0; + if ( uart->intr_works != polling ) + uart->intr_works = intr_off; pci_serial_early_init(uart); @@ -394,7 +399,7 @@ static void __init cf_check ns16550_init_irq(struct serial_port *port) static void ns16550_setup_postirq(struct ns16550 *uart) { - if ( uart->irq > 0 ) + if ( uart->intr_works != polling ) { /* Master interrupt enable; also keep DTR/RTS asserted. */ ns_write_reg(uart, @@ -473,6 +478,7 @@ static void __init cf_check ns16550_init_postirq(struct serial_port *port) if ( rc ) { uart->irq = 0; + uart->intr_works = polling; if ( msi_desc ) msi_free_irq(msi_desc); else @@ -488,7 +494,7 @@ static void __init cf_check ns16550_init_postirq(struct serial_port *port) } #endif - if ( uart->irq > 0 ) + if ( uart->intr_works != polling ) { uart->irqaction.handler = ns16550_interrupt; uart->irqaction.name = "ns16550"; @@ -595,7 +601,9 @@ static void __init cf_check ns16550_endboot(struct serial_port *port) static int __init cf_check ns16550_irq(struct serial_port *port) { struct ns16550 *uart = port->uart; - return ((uart->irq > 0) ? uart->irq : -1); + + return ( uart->intr_works != polling ) ? + uart->irq : -1; } static void cf_check ns16550_start_tx(struct serial_port *port) @@ -654,6 +662,9 @@ static void ns16550_init_common(struct ns16550 *uart) /* Default lsr_mask = UART_LSR_THRE */ uart->lsr_mask = UART_LSR_THRE; + + if ( console_has("polling") ) + uart->intr_works = polling; } #ifdef CONFIG_X86 @@ -1330,9 +1341,12 @@ pci_uart_config(struct ns16550 *uart, bool_t skip_amt, unsigned int idx) * as special only for X86. */ if ( uart->irq == 0xff ) + { uart->irq = 0; + uart->intr_works = polling; + } #endif - if ( !uart->irq ) + if ( !uart->irq || (uart->intr_works == polling) ) printk(XENLOG_INFO "ns16550: %pp: no legacy IRQ, using poll mode\n", &PCI_SBDF(0, b, d, f)); @@ -1552,6 +1566,7 @@ static bool __init parse_positional(struct ns16550 *uart, char **str) conf += 3; uart->msi = true; uart->irq = 0; + uart->intr_works = polling; } else #endif @@ -1791,8 +1806,11 @@ static int __init ns16550_uart_dt_init(struct dt_device_node *dev, } res = platform_get_irq(dev, 0); - if ( ! res ) - return -EINVAL; + if ( res < 0 ) + { + printk("there is no interrupt property, polling will be used\n"); + uart->intr_works = polling; + } uart->irq = res; uart->dw_usr_bsy = dt_device_is_compatible(dev, "snps,dw-apb-uart"); -- 2.41.0
