[Xen-devel] [PATCH RFC 1/6] xen/arm: platforms: Add earlyprintk and serial support for Tegra boards.

[Kyle Temkin <kyle@xxxxxxxxxxx>]

From: "Kyle J. Temkin" <temkink@xxxxxxxxxxxx>

Tegra boards feature a NS16550-compatible serial mapped into the MMIO
space. Add support for its use both as a full-featured serial port and
as an earlyprintk driver.

Adds a new "needs_rtoie" (requires Rx Timeout Interrupt) quirk, as some
platforms-- including Tegra-- require the NS16550 Rx timeout interrupt
to be enabled for receive to function properly. The same quirk is
applied in the eqvuialent Linux driver [1].

[1] 
https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=4539c24fe4f92c09ee668ef959d3e8180df619b9

Signed-off-by: Kyle Temkin <temkink@xxxxxxxxxxxx>
---
 xen/arch/arm/Rules.mk       |  1 +
 xen/drivers/char/ns16550.c  | 16 +++++++++++++++-
 xen/include/xen/8250-uart.h |  1 +
 3 files changed, 17 insertions(+), 1 deletion(-)

diff --git a/xen/arch/arm/Rules.mk b/xen/arch/arm/Rules.mk
index 93304be..2a1473a 100644
--- a/xen/arch/arm/Rules.mk
+++ b/xen/arch/arm/Rules.mk
@@ -44,6 +44,7 @@ EARLY_PRINTK_vexpress       := pl011,0x1c090000
 EARLY_PRINTK_xgene-mcdivitt := 8250,0x1c021000,2
 EARLY_PRINTK_xgene-storm    := 8250,0x1c020000,2
 EARLY_PRINTK_zynqmp         := cadence,0xff000000
+EARLY_PRINTK_tegra          := 8250,0x70006000,2
 
 ifneq ($(EARLY_PRINTK_$(CONFIG_EARLY_PRINTK)),)
 EARLY_PRINTK_CFG := $(subst $(comma), ,$(EARLY_PRINTK_$(CONFIG_EARLY_PRINTK)))
diff --git a/xen/drivers/char/ns16550.c b/xen/drivers/char/ns16550.c
index 1da103a..bffdb35 100644
--- a/xen/drivers/char/ns16550.c
+++ b/xen/drivers/char/ns16550.c
@@ -64,6 +64,7 @@ static struct ns16550 {
     unsigned int timeout_ms;
     bool_t intr_works;
     bool_t dw_usr_bsy;
+    bool_t needs_rtoie;
 #ifdef CONFIG_HAS_PCI
     /* PCI card parameters. */
     bool_t pb_bdf_enable;   /* if =1, pb-bdf effective, port behind bridge */
@@ -652,12 +653,23 @@ static void ns16550_setup_postirq(struct ns16550 *uart)
 {
     if ( uart->irq > 0 )
     {
+        u8 ier_value = 0;
+
         /* Master interrupt enable; also keep DTR/RTS asserted. */
         ns_write_reg(uart,
                      UART_MCR, UART_MCR_OUT2 | UART_MCR_DTR | UART_MCR_RTS);
 
         /* Enable receive interrupts. */
-        ns_write_reg(uart, UART_IER, UART_IER_ERDAI);
+        ier_value = UART_IER_ERDAI;
+
+        /*
+         * If we're on a platform that needs Rx timeouts enabled, also
+         * set Rx TimeOut Interrupt Enable (RTOIE).
+         */
+        if ( uart->needs_rtoie )
+          ier_value |= UART_IER_RTOIE;
+
+        ns_write_reg(uart, UART_IER, ier_value);
     }
 
     if ( uart->irq >= 0 )
@@ -1273,6 +1285,7 @@ static int __init ns16550_uart_dt_init(struct 
dt_device_node *dev,
     uart->irq = res;
 
     uart->dw_usr_bsy = dt_device_is_compatible(dev, "snps,dw-apb-uart");
+    uart->needs_rtoie = dt_device_is_compatible(dev, "nvidia,tegra20-uart");
 
     uart->vuart.base_addr = uart->io_base;
     uart->vuart.size = uart->io_size;
@@ -1293,6 +1306,7 @@ static const struct dt_device_match ns16550_dt_match[] 
__initconst =
     DT_MATCH_COMPATIBLE("ns16550"),
     DT_MATCH_COMPATIBLE("ns16550a"),
     DT_MATCH_COMPATIBLE("snps,dw-apb-uart"),
+    DT_MATCH_COMPATIBLE("nvidia,tegra20-uart"),
     { /* sentinel */ },
 };
 
diff --git a/xen/include/xen/8250-uart.h b/xen/include/xen/8250-uart.h
index c6b62c8..2ad0ee6 100644
--- a/xen/include/xen/8250-uart.h
+++ b/xen/include/xen/8250-uart.h
@@ -41,6 +41,7 @@
 #define UART_IER_ETHREI   0x02    /* tx reg. empty        */
 #define UART_IER_ELSI     0x04    /* rx line status       */
 #define UART_IER_EMSI     0x08    /* MODEM status         */
+#define UART_IER_RTOIE    0x10    /* rx timeout           */
 
 /* Interrupt Identificatiegister */
 #define UART_IIR_NOINT    0x01    /* no interrupt pending */
-- 
2.9.2


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