+++ /dev/null
-From 28c2408f991d97de5e3d1da9711cf5486f411d02 Mon Sep 17 00:00:00 2001
-From: Phil Elwell <phil@raspberrypi.org>
-Date: Thu, 11 Jul 2019 13:13:39 +0100
-Subject: [PATCH] tty: amba-pl011: Make TX optimisation conditional
-
-pl011_tx_chars takes a "from_irq" parameter to reduce the number of
-register accesses. When from_irq is true the function assumes that the
-FIFO is half empty and writes up to half a FIFO's worth of bytes
-without polling the FIFO status register, the reasoning being that
-the function is being called as a result of the TX interrupt being
-raised. This logic would work were it not for the fact that
-pl011_rx_chars, called from pl011_int before pl011_tx_chars, releases
-the spinlock before calling tty_flip_buffer_push.
-
-A user thread writing to the UART claims the spinlock and ultimately
-calls pl011_tx_chars with from_irq set to false. This reverts to the
-older logic that polls the FIFO status register before sending every
-byte. If this happen on an SMP system during the section of the IRQ
-handler where the spinlock has been released, then by the time the TX
-interrupt handler is called, the FIFO may already be full, and any
-further writes are likely to be lost.
-
-The fix involves adding a per-port flag that is true iff running from
-within the interrupt handler and the spinlock has not yet been released.
-This flag is then used as the value for the from_irq parameter of
-pl011_tx_chars, causing polling to be used in the unsafe case.
-
-Fixes: 1e84d22322ce ("serial/amba-pl011: Refactor and simplify TX FIFO handling")
-
-Signed-off-by: Phil Elwell <phil@raspberrypi.org>
----
- drivers/tty/serial/amba-pl011.c | 7 ++++++-
- 1 file changed, 6 insertions(+), 1 deletion(-)
-
---- a/drivers/tty/serial/amba-pl011.c
-+++ b/drivers/tty/serial/amba-pl011.c
-@@ -265,6 +265,7 @@ struct uart_amba_port {
- unsigned int old_cr; /* state during shutdown */
- unsigned int fixed_baud; /* vendor-set fixed baud rate */
- char type[12];
-+ bool irq_locked; /* in irq, unreleased lock */
- #ifdef CONFIG_DMA_ENGINE
- /* DMA stuff */
- bool using_tx_dma;
-@@ -811,6 +812,7 @@ __acquires(&uap->port.lock)
- if (!uap->using_tx_dma)
- return;
-
-+ uap->irq_locked = 0;
- dmaengine_terminate_async(uap->dmatx.chan);
-
- if (uap->dmatx.queued) {
-@@ -937,6 +939,7 @@ static void pl011_dma_rx_chars(struct ua
- fifotaken = pl011_fifo_to_tty(uap);
- }
-
-+ uap->irq_locked = 0;
- spin_unlock(&uap->port.lock);
- dev_vdbg(uap->port.dev,
- "Took %d chars from DMA buffer and %d chars from the FIFO\n",
-@@ -1341,6 +1344,7 @@ __acquires(&uap->port.lock)
- {
- pl011_fifo_to_tty(uap);
-
-+ uap->irq_locked = 0;
- spin_unlock(&uap->port.lock);
- tty_flip_buffer_push(&uap->port.state->port);
- /*
-@@ -1474,6 +1478,7 @@ static irqreturn_t pl011_int(int irq, vo
- int handled = 0;
-
- spin_lock_irqsave(&uap->port.lock, flags);
-+ uap->irq_locked = 1;
- status = pl011_read(uap, REG_RIS) & uap->im;
- if (status) {
- do {
-@@ -1493,7 +1498,7 @@ static irqreturn_t pl011_int(int irq, vo
- UART011_CTSMIS|UART011_RIMIS))
- pl011_modem_status(uap);
- if (status & UART011_TXIS)
-- pl011_tx_chars(uap, true);
-+ pl011_tx_chars(uap, uap->irq_locked);
-
- if (pass_counter-- == 0)
- break;
projects / openwrt / staging / chunkeey.git / blobdiff