[PULL 06/16] rust: pl011: Really use RX FIFO depth

[Paolo Bonzini]

While we model a 16-elements RX FIFO since the PL011 model was
introduced in commit cdbdb648b7c ("ARM Versatile Platform Baseboard
emulation"), we only read 1 char at a time!

Have can_receive() return how many elements are available, and use that
in receive().

This is the Rust version of commit 3e0f118f825 ("hw/char/pl011: Really
use RX FIFO depth"); but it also adds back a comment that is present
in commit f576e0733cc ("hw/char/pl011: Add support for loopback") and
absent in the Rust code.

Reviewed-by: Philippe Mathieu-Daudé <phi...@linaro.org>
Reviewed-by: Peter Maydell <peter.mayd...@linaro.org>
Signed-off-by: Paolo Bonzini <pbonz...@redhat.com>
---
 docs/devel/rust.rst              |  2 +-
 rust/hw/char/pl011/src/device.rs | 19 +++++++++++++------
 2 files changed, 14 insertions(+), 7 deletions(-)

diff --git a/docs/devel/rust.rst b/docs/devel/rust.rst
index 4de86375021..171d908e0b0 100644
--- a/docs/devel/rust.rst
+++ b/docs/devel/rust.rst
@@ -119,7 +119,7 @@ QEMU includes four crates:
   for the ``hw/char/pl011.c`` and ``hw/timer/hpet.c`` files.
 
 .. [#issues] The ``pl011`` crate is synchronized with ``hw/char/pl011.c``
-   as of commit 02b1f7f61928.  The ``hpet`` crate is synchronized as of
+   as of commit 3e0f118f82.  The ``hpet`` crate is synchronized as of
    commit 1433e38cc8.  Both are lacking tracing functionality.
 
 This section explains how to work with them.
diff --git a/rust/hw/char/pl011/src/device.rs b/rust/hw/char/pl011/src/device.rs
index 94b31659849..bde3be65c5b 100644
--- a/rust/hw/char/pl011/src/device.rs
+++ b/rust/hw/char/pl011/src/device.rs
@@ -580,19 +580,26 @@ fn write(&self, offset: hwaddr, value: u64, _size: u32) {
     fn can_receive(&self) -> u32 {
         let regs = self.regs.borrow();
         // trace_pl011_can_receive(s->lcr, s->read_count, r);
-        u32::from(regs.read_count < regs.fifo_depth())
+        regs.fifo_depth() - regs.read_count
     }
 
     fn receive(&self, buf: &[u8]) {
-        if buf.is_empty() {
+        let mut regs = self.regs.borrow_mut();
+        if regs.loopback_enabled() {
+            // In loopback mode, the RX input signal is internally disconnected
+            // from the entire receiving logics; thus, all inputs are ignored,
+            // and BREAK detection on RX input signal is also not performed.
             return;
         }
-        let mut regs = self.regs.borrow_mut();
-        let c: u32 = buf[0].into();
-        let update_irq = !regs.loopback_enabled() && 
regs.fifo_rx_put(c.into());
+
+        let mut update_irq = false;
+        for &c in buf {
+            let c: u32 = c.into();
+            update_irq |= regs.fifo_rx_put(c.into());
+        }
+
         // Release the BqlRefCell before calling self.update()
         drop(regs);
-
         if update_irq {
             self.update();
         }
-- 
2.49.0