[PATCH v3 1/8] serial: fake IRQ-regs context in poll handlers

[Jan Beulich <jbeulich@xxxxxxxx>]

In preparation of dropping the register parameters from
serial_[rt]x_interrupt() and in turn from IRQ handler functions,
register state needs making available another way for the few key
handlers which need it. Fake IRQ-like state.

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
---
The use of guest_cpu_user_regs() in dbc_uart_poll() is inconsistent with
other console poll functions we have, and it's unclear whether that's
actually generally correct.

Andrew suggested to move set_irq_regs() to BUGFRAME_run_fn handling;
it's not clear to me whether that would be (a) correct from an abstract
pov (that's exception, not interrupt context after all) and (b) really
beneficial.
---
v2: New.

--- a/xen/drivers/char/ehci-dbgp.c
+++ b/xen/drivers/char/ehci-dbgp.c
@@ -1253,6 +1253,7 @@ static void cf_check _ehci_dbgp_poll(str
     unsigned long flags;
     unsigned int timeout = MICROSECS(DBGP_CHECK_INTERVAL);
     bool empty = false;
+    struct cpu_user_regs *old_regs;
 
     if ( !dbgp->ehci_debug )
         return;
@@ -1268,12 +1269,17 @@ static void cf_check _ehci_dbgp_poll(str
         spin_unlock_irqrestore(&port->tx_lock, flags);
     }
 
+    /* Mimic interrupt context. */
+    old_regs = set_irq_regs(regs);
+
     if ( dbgp->in.chunk )
         serial_rx_interrupt(port, regs);
 
     if ( empty )
         serial_tx_interrupt(port, regs);
 
+    set_irq_regs(old_regs);
+
     if ( spin_trylock_irqsave(&port->tx_lock, flags) )
     {
         if ( dbgp->state == dbgp_idle && !dbgp->in.chunk &&
--- a/xen/drivers/char/ns16550.c
+++ b/xen/drivers/char/ns16550.c
@@ -211,10 +211,14 @@ static void cf_check __ns16550_poll(stru
 {
     struct serial_port *port = this_cpu(poll_port);
     struct ns16550 *uart = port->uart;
+    struct cpu_user_regs *old_regs;
 
     if ( uart->intr_works )
         return; /* Interrupts work - no more polling */
 
+    /* Mimic interrupt context. */
+    old_regs = set_irq_regs(regs);
+
     while ( ns_read_reg(uart, UART_LSR) & UART_LSR_DR )
     {
         if ( ns16550_ioport_invalid(uart) )
@@ -227,6 +231,7 @@ static void cf_check __ns16550_poll(stru
         serial_tx_interrupt(port, regs);
 
 out:
+    set_irq_regs(old_regs);
     set_timer(&uart->timer, NOW() + MILLISECS(uart->timeout_ms));
 }
 
--- a/xen/drivers/char/xhci-dbc.c
+++ b/xen/drivers/char/xhci-dbc.c
@@ -1164,6 +1164,7 @@ static void cf_check dbc_uart_poll(void
     struct dbc_uart *uart = port->uart;
     struct dbc *dbc = &uart->dbc;
     unsigned long flags = 0;
+    struct cpu_user_regs *old_regs;
 
     if ( spin_trylock_irqsave(&port->tx_lock, flags) )
     {
@@ -1175,10 +1176,15 @@ static void cf_check dbc_uart_poll(void
         spin_unlock_irqrestore(&port->tx_lock, flags);
     }
 
+    /* Mimic interrupt context. */
+    old_regs = set_irq_regs(guest_cpu_user_regs());
+
     while ( dbc_work_ring_size(&dbc->dbc_iwork) )
         serial_rx_interrupt(port, guest_cpu_user_regs());
 
     serial_tx_interrupt(port, guest_cpu_user_regs());
+
+    set_irq_regs(old_regs);
     set_timer(&uart->timer, NOW() + MICROSECS(DBC_POLL_INTERVAL));
 }