[PATCH 2/2] ns16550: add Exar dual PCIe UART card support

["Marek Marczykowski-Górecki" <marmarek@invisiblethingslab.com>]

Besides standard UART setup, this device needs enabling
(vendor-specific) "Enhanced Control Bits" - otherwise disabling hardware
control flow (MCR[2]) is ignored. Add appropriate quirk to the
ns16550_setup_preirq(), similar to the handle_dw_usr_busy_quirk(). The
new function act on Exar cards only (based on vendor ID).

Additionally, Exar card supports fractional divisor (DLD[3:0] register,
at 0x10). This part is not supported here yet, and seems to not
be required for working 115200bps at the very least.

Signed-off-by: Marek Marczykowski-Górecki <marmarek@invisiblethingslab.com>
---
 xen/drivers/char/ns16550.c  | 39 +++++++++++++++++++++++++++++++++++--
 xen/include/xen/8250-uart.h |  4 ++++
 xen/include/xen/pci_ids.h   |  2 ++
 3 files changed, 43 insertions(+), 2 deletions(-)

diff --git a/xen/drivers/char/ns16550.c b/xen/drivers/char/ns16550.c
index 97b85b0225cc..540124b198df 100644
--- a/xen/drivers/char/ns16550.c
+++ b/xen/drivers/char/ns16550.c
@@ -88,6 +88,7 @@ struct ns16550_config {
         param_pericom_2port,
         param_pericom_4port,
         param_pericom_8port,
+        param_exar_xr17v3521,
     } param;
 };
 
@@ -169,6 +170,21 @@ static void handle_dw_usr_busy_quirk(struct ns16550 *uart)
     }
 }
 
+static void enable_exar_enhanced_bits(struct ns16550 *uart)
+{
+#ifdef NS16550_PCI
+    if ( uart->bar &&
+         pci_conf_read16(PCI_SBDF(0, uart->ps_bdf[0], uart->ps_bdf[2],
+                         uart->ps_bdf[2]), PCI_VENDOR_ID) == PCI_VENDOR_ID_EXAR )
+    {
+        /* Exar cards ignores setting MCR[2] (hardware flow control) unless
+         * "Enhanced control bits" is enabled.
+         */
+        ns_write_reg(uart, UART_XR_EFR, UART_EFR_ECB);
+    }
+#endif
+}
+
 static void ns16550_interrupt(
     int irq, void *dev_id, struct cpu_user_regs *regs)
 {
@@ -303,6 +319,9 @@ static void ns16550_setup_preirq(struct ns16550 *uart)
     /* Handle the DesignWare 8250 'busy-detect' quirk. */
     handle_dw_usr_busy_quirk(uart);
 
+    /* Enable Exar "Enhanced function bits" */
+    enable_exar_enhanced_bits(uart);
+
     /* Line control and baud-rate generator. */
     ns_write_reg(uart, UART_LCR, lcr | UART_LCR_DLAB);
     if ( uart->baud != BAUD_AUTO )
@@ -781,7 +800,17 @@ static const struct ns16550_config_param __initconst uart_param[] = {
         .lsr_mask = UART_LSR_THRE,
         .bar0 = 1,
         .max_ports = 8,
-    }
+    },
+    [param_exar_xr17v3521] = {
+        .base_baud = 7812500,
+        .uart_offset = 0x400,
+        .reg_width = 1,
+        .fifo_size = 256,
+        .lsr_mask = UART_LSR_THRE,
+        .bar0 = 1,
+        .mmio = 1,
+        .max_ports = 2,
+    },
 };
 
 static const struct ns16550_config __initconst uart_config[] =
@@ -1007,7 +1036,13 @@ static const struct ns16550_config __initconst uart_config[] =
         .vendor_id = PCI_VENDOR_ID_PERICOM,
         .dev_id = 0x7958,
         .param = param_pericom_8port
-    }
+    },
+    /* Exar Corp. XR17V3521 Dual PCIe UART */
+    {
+        .vendor_id = PCI_VENDOR_ID_EXAR,
+        .dev_id = 0x0352,
+        .param = param_exar_xr17v3521
+    },
 };
 
 static int __init
diff --git a/xen/include/xen/8250-uart.h b/xen/include/xen/8250-uart.h
index 5c3bac33221e..8c12fbbb3d5a 100644
--- a/xen/include/xen/8250-uart.h
+++ b/xen/include/xen/8250-uart.h
@@ -121,6 +121,10 @@
 /* Frequency of external clock source. This definition assumes PC platform. */
 #define UART_CLOCK_HZ     1843200
 
+/* Exar specific */
+#define UART_XR_EFR       0x09
+#define UART_EFR_ECB      0x10
+
 /* Resume retry settings */
 #define RESUME_DELAY      MILLISECS(10)
 #define RESUME_RETRIES    100
diff --git a/xen/include/xen/pci_ids.h b/xen/include/xen/pci_ids.h
index 7788ba9d2f34..e798477a7e23 100644
--- a/xen/include/xen/pci_ids.h
+++ b/xen/include/xen/pci_ids.h
@@ -4,6 +4,8 @@
 
 #define PCI_VENDOR_ID_PERICOM            0x12d8
 
+#define PCI_VENDOR_ID_EXAR               0x13a8
+
 #define PCI_VENDOR_ID_OXSEMI             0x1415
 
 #define PCI_VENDOR_ID_BROADCOM           0x14e4
-- 
2.31.1