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[Qemu-devel] [PULL 46/52] char/cadence_uart: Implement Tx flow control
From: |
Peter Maydell |
Subject: |
[Qemu-devel] [PULL 46/52] char/cadence_uart: Implement Tx flow control |
Date: |
Mon, 6 Jan 2014 11:30:51 +0000 |
From: Peter Crosthwaite <address@hidden>
If the UART back-end blocks, buffer in the Tx FIFO to try again later.
This stops the IO-thread busy waiting on char back-ends (which causes
all sorts of performance problems).
Signed-off-by: Peter Crosthwaite <address@hidden>
Message-id: address@hidden
Signed-off-by: Peter Maydell <address@hidden>
---
hw/char/cadence_uart.c | 31 +++++++++++++++++++++++++++++--
1 file changed, 29 insertions(+), 2 deletions(-)
diff --git a/hw/char/cadence_uart.c b/hw/char/cadence_uart.c
index 8a9ef81..1012f1a 100644
--- a/hw/char/cadence_uart.c
+++ b/hw/char/cadence_uart.c
@@ -286,6 +286,34 @@ static void uart_write_rx_fifo(void *opaque, const uint8_t
*buf, int size)
uart_update_status(s);
}
+static gboolean cadence_uart_xmit(GIOChannel *chan, GIOCondition cond,
+ void *opaque)
+{
+ UartState *s = opaque;
+ int ret;
+
+ /* instant drain the fifo when there's no back-end */
+ if (!s->chr) {
+ s->tx_count = 0;
+ }
+
+ if (!s->tx_count) {
+ return FALSE;
+ }
+
+ ret = qemu_chr_fe_write(s->chr, s->tx_fifo, s->tx_count);
+ s->tx_count -= ret;
+ memmove(s->tx_fifo, s->tx_fifo + ret, s->tx_count);
+
+ if (s->tx_count) {
+ int r = qemu_chr_fe_add_watch(s->chr, G_IO_OUT, cadence_uart_xmit, s);
+ assert(r);
+ }
+
+ uart_update_status(s);
+ return FALSE;
+}
+
static void uart_write_tx_fifo(UartState *s, const uint8_t *buf, int size)
{
if ((s->r[R_CR] & UART_CR_TX_DIS) || !(s->r[R_CR] & UART_CR_TX_EN)) {
@@ -306,8 +334,7 @@ static void uart_write_tx_fifo(UartState *s, const uint8_t
*buf, int size)
memcpy(s->tx_fifo + s->tx_count, buf, size);
s->tx_count += size;
- qemu_chr_fe_write_all(s->chr, s->tx_fifo, s->tx_count);
- s->tx_count = 0;
+ cadence_uart_xmit(NULL, G_IO_OUT, s);
}
static void uart_receive(void *opaque, const uint8_t *buf, int size)
--
1.8.5
- [Qemu-devel] [PULL 15/52] target-arm: A64: Implement minimal set of EL0-visible sysregs, (continued)
- [Qemu-devel] [PULL 15/52] target-arm: A64: Implement minimal set of EL0-visible sysregs, Peter Maydell, 2014/01/06
- [Qemu-devel] [PULL 18/52] target-arm: A64: add support for conditional compare insns, Peter Maydell, 2014/01/06
- [Qemu-devel] [PULL 17/52] target-arm: A64: add support for add/sub with carry, Peter Maydell, 2014/01/06
- [Qemu-devel] [PULL 10/52] target-arm: A64: implement FMOV, Peter Maydell, 2014/01/06
- [Qemu-devel] [PULL 52/52] hw: arm_gic: Introduce gic_set_priority function, Peter Maydell, 2014/01/06
- [Qemu-devel] [PULL 51/52] arm_gic: Rename GIC_X_TRIGGER to GIC_X_EDGE_TRIGGER, Peter Maydell, 2014/01/06
- [Qemu-devel] [PULL 16/52] target-arm: Widen thread-local register state fields to 64 bits, Peter Maydell, 2014/01/06
- [Qemu-devel] [PULL 49/52] arm/xilinx_zynq: Always instantiate the GEMs, Peter Maydell, 2014/01/06
- [Qemu-devel] [PULL 48/52] target-arm: remove raw_read|write duplication, Peter Maydell, 2014/01/06
- [Qemu-devel] [PULL 50/52] target-arm: fix build with gcc 4.8.2, Peter Maydell, 2014/01/06
- [Qemu-devel] [PULL 46/52] char/cadence_uart: Implement Tx flow control,
Peter Maydell <=
- [Qemu-devel] [PULL 43/52] char/cadence_uart: Fix can_receive logic, Peter Maydell, 2014/01/06
- [Qemu-devel] [PULL 44/52] char/cadence_uart: Use the TX fifo for transmission, Peter Maydell, 2014/01/06
- [Qemu-devel] [PULL 41/52] char/cadence_uart: Define Missing SR/ISR fields, Peter Maydell, 2014/01/06
- [Qemu-devel] [PULL 40/52] char/cadence_uart: Simplify status generation, Peter Maydell, 2014/01/06
- [Qemu-devel] [PULL 39/52] char/cadence_uart: s/r_fifo/rx_fifo, Peter Maydell, 2014/01/06
- [Qemu-devel] [PULL 38/52] char/cadence_uart: Fix reset., Peter Maydell, 2014/01/06
- [Qemu-devel] [PULL 37/52] char/cadence_uart: Add missing uart_update_state, Peter Maydell, 2014/01/06
- [Qemu-devel] [PULL 47/52] target-arm: use c13_context field for CONTEXTIDR, Peter Maydell, 2014/01/06
- [Qemu-devel] [PULL 36/52] char/cadence_uart: Mark struct fields as public/private, Peter Maydell, 2014/01/06
- [Qemu-devel] [PULL 35/52] target-arm: Give the FPSCR rounding modes names, Peter Maydell, 2014/01/06