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It seems that when the transmit FIFO threshold is reached on OMAP UARTs, it does not result in a PRCM wakeup. This appears to be a silicon bug. This means that if the MPU powerdomain is in a low-power state, the MPU will not be awakened to refill the FIFO until the next interrupt from another device. The best solution, at least for the short term, would be for the OMAP serial driver to call a OMAP subarchitecture function to prevent the MPU powerdomain from entering a low power state while the FIFO has data to transmit. However, we no longer have a clean way to do this, since patches that add platform_data function pointers have been deprecated by the OMAP maintainer. So we attempt to work around this as well. The workarounds depend on the setting of CONFIG_CPU_IDLE. When CONFIG_CPU_IDLE=n, the driver will now only transmit one byte at a time. This causes the transmit FIFO threshold interrupt to stay active until there is no more data to be sent. Thus, the MPU powerdomain stays on during transmits. Aside from that energy consumption penalty, each transmitted byte results in a huge number of UART interrupts -- about five per byte. This wastes CPU time and is quite inefficient, but is probably the most expedient workaround in this case. When CONFIG_CPU_IDLE=y, there is a slightly more direct workaround: the PM QoS constraint can be abused to keep the MPU powerdomain on. This results in a normal number of interrupts, but, similar to the above workaround, wastes power by preventing the MPU from entering WFI. Future patches are planned for the 3.4 merge window to implement more efficient, but also more disruptive, workarounds to these problems. DMA operation is unaffected by this patch. Signed-off-by: Paul Walmsley <paul@pwsan.com> Cc: Tomi Valkeinen <tomi.valkeinen@ti.com> Cc: Govindraj Raja <govindraj.r@ti.com> Cc: Kevin Hilman <khilman@ti.com> Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de> |
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| .. | ||
| 8250 | ||
| cpm_uart | ||
| jsm | ||
| 21285.c | ||
| 68328serial.c | ||
| 68328serial.h | ||
| altera_jtaguart.c | ||
| altera_uart.c | ||
| amba-pl010.c | ||
| amba-pl011.c | ||
| apbuart.c | ||
| apbuart.h | ||
| ar933x_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 | ||
| dz.c | ||
| dz.h | ||
| icom.c | ||
| icom.h | ||
| ifx6x60.c | ||
| ifx6x60.h | ||
| imx.c | ||
| ioc3_serial.c | ||
| ioc4_serial.c | ||
| ip22zilog.c | ||
| ip22zilog.h | ||
| Kconfig | ||
| kgdboc.c | ||
| lantiq.c | ||
| Makefile | ||
| max3100.c | ||
| max3107-aava.c | ||
| max3107.c | ||
| max3107.h | ||
| mcf.c | ||
| mfd.c | ||
| mpc52xx_uart.c | ||
| mpsc.c | ||
| mrst_max3110.c | ||
| mrst_max3110.h | ||
| msm_serial_hs.c | ||
| msm_serial.c | ||
| msm_serial.h | ||
| msm_smd_tty.c | ||
| mux.c | ||
| mxs-auart.c | ||
| netx-serial.c | ||
| nwpserial.c | ||
| of_serial.c | ||
| omap-serial.c | ||
| pch_uart.c | ||
| pmac_zilog.c | ||
| pmac_zilog.h | ||
| pnx8xxx_uart.c | ||
| pxa.c | ||
| sa1100.c | ||
| samsung.c | ||
| samsung.h | ||
| sb1250-duart.c | ||
| sc26xx.c | ||
| serial_core.c | ||
| serial_ks8695.c | ||
| serial_txx9.c | ||
| sh-sci.c | ||
| sh-sci.h | ||
| sirfsoc_uart.c | ||
| sirfsoc_uart.h | ||
| sn_console.c | ||
| suncore.c | ||
| suncore.h | ||
| sunhv.c | ||
| sunsab.c | ||
| sunsab.h | ||
| sunsu.c | ||
| sunzilog.c | ||
| sunzilog.h | ||
| timbuart.c | ||
| timbuart.h | ||
| uartlite.c | ||
| ucc_uart.c | ||
| vr41xx_siu.c | ||
| vt8500_serial.c | ||
| xilinx_uartps.c | ||
| zs.c | ||
| zs.h | ||