diff options
Diffstat (limited to 'target/linux/bcm27xx/patches-5.4/950-0266-tty-amba-pl011-Make-TX-optimisation-conditional.patch')
| -rw-r--r-- | target/linux/bcm27xx/patches-5.4/950-0266-tty-amba-pl011-Make-TX-optimisation-conditional.patch | 85 |
1 files changed, 85 insertions, 0 deletions
diff --git a/target/linux/bcm27xx/patches-5.4/950-0266-tty-amba-pl011-Make-TX-optimisation-conditional.patch b/target/linux/bcm27xx/patches-5.4/950-0266-tty-amba-pl011-Make-TX-optimisation-conditional.patch new file mode 100644 index 0000000000..9214bda206 --- /dev/null +++ b/target/linux/bcm27xx/patches-5.4/950-0266-tty-amba-pl011-Make-TX-optimisation-conditional.patch @@ -0,0 +1,85 @@ +From 76e24a2218069fadb28c0c2f5d813302ad5f85a3 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 +@@ -270,6 +270,7 @@ 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; +@@ -813,6 +814,7 @@ __acquires(&uap->port.lock) + if (!uap->using_tx_dma) + return; + ++ uap->irq_locked = 0; + dmaengine_terminate_async(uap->dmatx.chan); + + if (uap->dmatx.queued) { +@@ -939,6 +941,7 @@ 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", +@@ -1347,6 +1350,7 @@ __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); + /* +@@ -1482,6 +1486,7 @@ 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 { +@@ -1501,7 +1506,7 @@ 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; |