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9d297239b8
The IMX UART has a 32 bytes HW buffer which can be filled up in
2777us at 115200 baud or 80us at 4Mbaud (supported by IMX53).
Taking this in consideration there is a good probability to lose
data because of the DMA startup latency.
Our tests (explained below) indicates a latency up to 4400us when
creating interrupt load and ~70us without. When creating interrupt
load I was able to see continuous overrun errors by checking serial
driver statistics using the command:
`cat /proc/tty/driver/IMX-uart`.
Replace manual restart of DMA with cyclic DMA to eliminate data loss
due to DMA engine startup latency (similar approch to atmel_serial.c
driver). As result the DMA engine will start on the first serial data
transfer and stops only when serial port is closed.
Tests environment:
Using the m53evk board I have used a GPIO for profiling the IMX
serial driver.
- The RX line and GPIO were connected to oscilloscope.
- Run a small test program on the m53evk board that will only open
and read data from ttymxc2 port.
- Connect the ttymxc2 port to my laptop using a USB serial converter
where another test program is running, able to send configurable
packet lengths and intervals.
- Serial ports configured at 115200 8N1.
- Interrupts load created by disconnecting/connecting (3s interval)
a USB hub, using a digital switch, with 4 USB devices (USB-Serial
converter, USB SD card, etc) connected.
(around 160 interrupts/second generated)
- The GPIO was toggled HI in the `imx_int` when USR1_RRDY or USR1_AGTIM
events are received and toggled back, once the DMA configuration
is finalized, at the end of `imx_dma_rxint`.
Measurements:
The measurements were done from the end of the last byte (RX line) until
the GPIO was toggled back LOW.
Note: The GPIO toggling was done using `gpiod_set_value` method.
Tests performed:
1. Sending 9 bytes packets at 8ms interval. Having the 9 bytes packets
will activate the RRDY threshold event and IMX serial interrupt
called.
Results:
- DMA start latency (interrupt start latency +
DMA configuration) consistently 70us when system not loaded.
- DMA start latency up to 4400us when system loaded.
2. Sending 40 bytes packet at 8mS interval.
Results with load:
- Able to observe overruns by running:
`watch -n1 cat /proc/tty/driver/IMX-uart`
Tested-by: Peter Senna Tschudin <peter.senna@collabora.com>
Acked-by: Peter Senna Tschudin <peter.senna@collabora.com>
Signed-off-by: Nandor Han <nandor.han@ge.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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| .. | ||
| 8250 | ||
| cpm_uart | ||
| jsm | ||
| 21285.c | ||
| altera_jtaguart.c | ||
| altera_uart.c | ||
| amba-pl010.c | ||
| amba-pl011.c | ||
| amba-pl011.h | ||
| apbuart.c | ||
| apbuart.h | ||
| ar933x_uart.c | ||
| arc_uart.c | ||
| atmel_serial.c | ||
| bcm63xx_uart.c | ||
| bfin_sport_uart.c | ||
| bfin_sport_uart.h | ||
| bfin_uart.c | ||
| clps711x.c | ||
| crisv10.c | ||
| crisv10.h | ||
| digicolor-usart.c | ||
| dz.c | ||
| dz.h | ||
| earlycon-arm-semihost.c | ||
| earlycon.c | ||
| efm32-uart.c | ||
| etraxfs-uart.c | ||
| fsl_lpuart.c | ||
| icom.c | ||
| icom.h | ||
| ifx6x60.c | ||
| ifx6x60.h | ||
| imx.c | ||
| ioc3_serial.c | ||
| ioc4_serial.c | ||
| ip22zilog.c | ||
| ip22zilog.h | ||
| Kconfig | ||
| kgdb_nmi.c | ||
| kgdboc.c | ||
| lantiq.c | ||
| lpc32xx_hs.c | ||
| m32r_sio_reg.h | ||
| m32r_sio.c | ||
| Makefile | ||
| max310x.c | ||
| max3100.c | ||
| mcf.c | ||
| men_z135_uart.c | ||
| meson_uart.c | ||
| mpc52xx_uart.c | ||
| mps2-uart.c | ||
| mpsc.c | ||
| msm_serial.c | ||
| mux.c | ||
| mvebu-uart.c | ||
| mxs-auart.c | ||
| netx-serial.c | ||
| omap-serial.c | ||
| pch_uart.c | ||
| pic32_uart.c | ||
| pic32_uart.h | ||
| pmac_zilog.c | ||
| pmac_zilog.h | ||
| pnx8xxx_uart.c | ||
| pxa.c | ||
| rp2.c | ||
| sa1100.c | ||
| samsung.c | ||
| samsung.h | ||
| sb1250-duart.c | ||
| sc16is7xx.c | ||
| sccnxp.c | ||
| serial_core.c | ||
| serial_ks8695.c | ||
| serial_mctrl_gpio.c | ||
| serial_mctrl_gpio.h | ||
| serial_txx9.c | ||
| serial-tegra.c | ||
| sh-sci.c | ||
| sh-sci.h | ||
| sirfsoc_uart.c | ||
| sirfsoc_uart.h | ||
| sn_console.c | ||
| sprd_serial.c | ||
| st-asc.c | ||
| stm32-usart.c | ||
| suncore.c | ||
| sunhv.c | ||
| sunsab.c | ||
| sunsab.h | ||
| sunsu.c | ||
| sunzilog.c | ||
| sunzilog.h | ||
| tilegx.c | ||
| timbuart.c | ||
| timbuart.h | ||
| uartlite.c | ||
| ucc_uart.c | ||
| vr41xx_siu.c | ||
| vt8500_serial.c | ||
| xilinx_uartps.c | ||
| zs.c | ||
| zs.h | ||