ns16550: add Exar PCIe UART cards support

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 2-, 4-, and 8- port cards only. I have tested
the functionality on 2-port card but based on the Linux driver, the same
applies to other models too.

Additionally, Exar card supports fractional divisor (DLD[3:0] register,
at 0x02). This part is not supported here yet, and seems to not
be required for working 115200bps at the very least.

The specification for the 2-port card is available at:
https://www.maxlinear.com/product/interface/uarts/pcie-uarts/xr17v352

Signed-off-by: Marek Marczykowski-Górecki <marmarek@invisiblethingslab.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>

xen/drivers/char/ns16550.c

@@ -88,6 +88,9 @@ struct ns16550_config {
         param_pericom_2port,
         param_pericom_4port,
         param_pericom_8port,
+        param_exar_xr17v352,
+        param_exar_xr17v354,
+        param_exar_xr17v358,
     } param;
 };
 
@@ -104,6 +107,8 @@ struct ns16550_config_param {
     unsigned int uart_offset;
     unsigned int first_offset;
 };
+
+static void enable_exar_enhanced_bits(const struct ns16550 *uart);
 #endif
 
 static void ns16550_delayed_resume(void *data);
@@ -303,6 +308,11 @@ static void ns16550_setup_preirq(struct ns16550 *uart)
     /* Handle the DesignWare 8250 'busy-detect' quirk. */
     handle_dw_usr_busy_quirk(uart);
 
+#ifdef CONFIG_HAS_PCI
+    /* Enable Exar "Enhanced function bits" */
+    enable_exar_enhanced_bits(uart);
+#endif
+
     /* Line control and baud-rate generator. */
     ns_write_reg(uart, UART_LCR, lcr | UART_LCR_DLAB);
     if ( uart->baud != BAUD_AUTO )
@@ -781,7 +791,37 @@ static const struct ns16550_config_param __initconst uart_param[] = {
         .lsr_mask = UART_LSR_THRE,
         .bar0 = 1,
         .max_ports = 8,
-    }
+    },
+    [param_exar_xr17v352] = {
+        .base_baud = 7812500,
+        .uart_offset = 0x400,
+        .reg_width = 1,
+        .fifo_size = 256,
+        .lsr_mask = UART_LSR_THRE,
+        .bar0 = 1,
+        .mmio = 1,
+        .max_ports = 2,
+    },
+    [param_exar_xr17v354] = {
+        .base_baud = 7812500,
+        .uart_offset = 0x400,
+        .reg_width = 1,
+        .fifo_size = 256,
+        .lsr_mask = UART_LSR_THRE,
+        .bar0 = 1,
+        .mmio = 1,
+        .max_ports = 4,
+    },
+    [param_exar_xr17v358] = {
+        .base_baud = 7812500,
+        .uart_offset = 0x400,
+        .reg_width = 1,
+        .fifo_size = 256,
+        .lsr_mask = UART_LSR_THRE,
+        .bar0 = 1,
+        .mmio = 1,
+        .max_ports = 8,
+    },
 };
 
 static const struct ns16550_config __initconst uart_config[] =
@@ -1007,7 +1047,25 @@ static const struct ns16550_config __initconst uart_config[] =
         .vendor_id = PCI_VENDOR_ID_PERICOM,
         .dev_id = 0x7958,
         .param = param_pericom_8port
-    }
+    },
+    /* Exar Corp. XR17V352 Dual PCIe UART */
+    {
+        .vendor_id = PCI_VENDOR_ID_EXAR,
+        .dev_id = 0x0352,
+        .param = param_exar_xr17v352
+    },
+    /* Exar Corp. XR17V354 Quad PCIe UART */
+    {
+        .vendor_id = PCI_VENDOR_ID_EXAR,
+        .dev_id = 0x0354,
+        .param = param_exar_xr17v354
+    },
+    /* Exar Corp. XR17V358 Octal PCIe UART */
+    {
+        .vendor_id = PCI_VENDOR_ID_EXAR,
+        .dev_id = 0x0358,
+        .param = param_exar_xr17v358
+    },
 };
 
 static int __init
@@ -1177,6 +1235,27 @@ pci_uart_config(struct ns16550 *uart, bool_t skip_amt, unsigned int idx)
     return 0;
 }
 
+static void enable_exar_enhanced_bits(const struct ns16550 *uart)
+{
+    uint8_t efr;
+
+    switch ( uart->param - uart_param )
+    {
+    case param_exar_xr17v352:
+    case param_exar_xr17v354:
+    case param_exar_xr17v358:
+        /*
+         * Exar XR17V35x cards ignore setting MCR[2] (hardware flow control)
+         * unless "Enhanced control bits" is enabled.
+         * The below checks for a 2, 4 or 8 port UART, following Linux driver.
+         */
+        efr = ns_read_reg(uart, UART_XR_EFR);
+        efr |= UART_EFR_ECB;
+        ns_write_reg(uart, UART_XR_EFR, efr);
+        break;
+    }
+}
+
 #endif /* CONFIG_HAS_PCI */
 
 /*

xen/include/xen/8250-uart.h

@@ -35,6 +35,7 @@
 #define UART_USR          0x1f    /* Status register (DW) */
 #define UART_DLL          0x00    /* divisor latch (ls) (DLAB=1) */
 #define UART_DLM          0x01    /* divisor latch (ms) (DLAB=1) */
+#define UART_XR_EFR       0x09    /* Enhanced function register (Exar) */
 
 /* Interrupt Enable Register */
 #define UART_IER_ERDAI    0x01    /* rx data recv'd       */
@@ -121,6 +122,9 @@
 /* Frequency of external clock source. This definition assumes PC platform. */
 #define UART_CLOCK_HZ     1843200
 
+/* Bits in Exar specific UART_XR_EFR register */
+#define UART_EFR_ECB      0x10
+
 /* Resume retry settings */
 #define RESUME_DELAY      MILLISECS(10)
 #define RESUME_RETRIES    100

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