From mboxrd@z Thu Jan 1 00:00:00 1970 From: govindraj.ti@gmail.com (Govindraj) Date: Mon, 23 Jan 2012 14:20:34 +0530 Subject: [PATCH 2/2] tty: serial: OMAP: transmit FIFO threshold interrupts don't wake the chip In-Reply-To: <20120121072740.18707.87632.stgit@dusk> References: <20120121071934.18707.64258.stgit@dusk> <20120121072740.18707.87632.stgit@dusk> Message-ID: To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On Sat, Jan 21, 2012 at 12:57 PM, Paul Walmsley wrote: > 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. > With these two patches number of interrupts seems to increase by 24x after boot up. [...] / # cat /proc/interrupts | grep "UART2" 74: 3902 INTC OMAP UART2 / # [...] without these two patches + cpu_idle enabled [...] / # / # cat /proc/interrupts | grep "UART2" 74: 158 INTC OMAP UART2 / # [...] I am using beagle xm and 3.3rc1 Looks like there are far two many uart irqs which keeps the mpu busy and thus preventing uart sluggishness. -- Thanks, Govindraj.R > DMA operation is unaffected by this patch. > > Signed-off-by: Paul Walmsley > Cc: Tomi Valkeinen > Cc: Govindraj Raja > Cc: Kevin Hilman > --- > ?arch/arm/plat-omap/include/plat/omap-serial.h | ? ?1 > ?drivers/tty/serial/omap-serial.c ? ? ? ? ? ? ?| ? 51 +++++++++++++++++++++++++ > ?2 files changed, 51 insertions(+), 1 deletions(-) > > diff --git a/arch/arm/plat-omap/include/plat/omap-serial.h b/arch/arm/plat-omap/include/plat/omap-serial.h > index 9ff4444..12a64eb 100644 > --- a/arch/arm/plat-omap/include/plat/omap-serial.h > +++ b/arch/arm/plat-omap/include/plat/omap-serial.h > @@ -131,6 +131,7 @@ struct uart_omap_port { > ? ? ? ?u32 ? ? ? ? ? ? ? ? ? ? context_loss_cnt; > ? ? ? ?u32 ? ? ? ? ? ? ? ? ? ? errata; > ? ? ? ?u8 ? ? ? ? ? ? ? ? ? ? ?wakeups_enabled; > + ? ? ? u8 ? ? ? ? ? ? ? ? ? ? ?max_tx_count; > > ? ? ? ?struct pm_qos_request ? pm_qos_request; > ? ? ? ?u32 ? ? ? ? ? ? ? ? ? ? latency; > diff --git a/drivers/tty/serial/omap-serial.c b/drivers/tty/serial/omap-serial.c > index 9de7d71..621fde5 100644 > --- a/drivers/tty/serial/omap-serial.c > +++ b/drivers/tty/serial/omap-serial.c > @@ -88,6 +88,49 @@ static inline void serial_omap_clear_fifos(struct uart_omap_port *up) > ? ? ? ?serial_out(up, UART_FCR, 0); > ?} > > +/** > + * serial_omap_block_cpu_low_power_state - prevent MPU pwrdm from leaving ON > + * @up: struct uart_omap_port * > + * > + * Prevent the MPU powerdomain from entering a power state lower than > + * ON. ?(It should be sufficient to prevent it from entering INACTIVE, > + * but there is presently no easy way to do this.) ?This works around > + * a suspected silicon bug in the OMAP UART IP blocks. ?The UARTs should > + * wake the PRCM when the transmit FIFO threshold interrupt is raised, but > + * they do not. ? See also serial_omap_allow_cpu_low_power_state(). ?No > + * return value. > + */ > +static void serial_omap_block_cpu_low_power_state(struct uart_omap_port *up) > +{ > +#ifdef CONFIG_CPU_IDLE > + ? ? ? up->latency = 1; > + ? ? ? schedule_work(&up->qos_work); > +#else > + ? ? ? up->max_tx_count = 1; > +#endif > +} > + > +/** > + * serial_omap_allow_cpu_low_power_state - remove power state restriction on MPU > + * @up: struct uart_omap_port * > + * > + * Cancel the effects of serial_omap_block_cpu_low_power_state(). > + * This should allow the MPU powerdomain to enter a power state lower > + * than ON, assuming the rest of the kernel is not restricting it. > + * This works around a suspected silicon bug in the OMAP UART IP > + * blocks. ?The UARTs should wake the PRCM when the transmit FIFO > + * threshold interrupt is raised, but they do not. ?No return value. > + */ > +static void serial_omap_allow_cpu_low_power_state(struct uart_omap_port *up) > +{ > +#ifdef CONFIG_CPU_IDLE > + ? ? ? up->latency = up->calc_latency; > + ? ? ? schedule_work(&up->qos_work); > +#else > + ? ? ? up->max_tx_count = up->port.fifosize / 4; > +#endif > +} > + > ?/* > ?* serial_omap_get_divisor - calculate divisor value > ?* @port: uart port info > @@ -163,6 +206,9 @@ static void serial_omap_stop_tx(struct uart_port *port) > ? ? ? ? ? ? ? ?serial_out(up, UART_IER, up->ier); > ? ? ? ?} > > + ? ? ? if (!up->use_dma) > + ? ? ? ? ? ? ? serial_omap_allow_cpu_low_power_state(up); > + > ? ? ? ?pm_runtime_mark_last_busy(&up->pdev->dev); > ? ? ? ?pm_runtime_put_autosuspend(&up->pdev->dev); > ?} > @@ -264,7 +310,7 @@ static void transmit_chars(struct uart_omap_port *up) > ? ? ? ? ? ? ? ?serial_omap_stop_tx(&up->port); > ? ? ? ? ? ? ? ?return; > ? ? ? ?} > - ? ? ? count = up->port.fifosize / 4; > + ? ? ? count = up->max_tx_count; > ? ? ? ?do { > ? ? ? ? ? ? ? ?serial_out(up, UART_TX, xmit->buf[xmit->tail]); > ? ? ? ? ? ? ? ?xmit->tail = (xmit->tail + 1) & (UART_XMIT_SIZE - 1); > @@ -297,6 +343,7 @@ static void serial_omap_start_tx(struct uart_port *port) > > ? ? ? ?if (!up->use_dma) { > ? ? ? ? ? ? ? ?pm_runtime_get_sync(&up->pdev->dev); > + ? ? ? ? ? ? ? serial_omap_block_cpu_low_power_state(up); > ? ? ? ? ? ? ? ?serial_omap_enable_ier_thri(up); > ? ? ? ? ? ? ? ?pm_runtime_mark_last_busy(&up->pdev->dev); > ? ? ? ? ? ? ? ?pm_runtime_put_autosuspend(&up->pdev->dev); > @@ -1421,6 +1468,8 @@ static int serial_omap_probe(struct platform_device *pdev) > ? ? ? ?up->port.fifosize = 64; > ? ? ? ?up->port.ops = &serial_omap_pops; > > + ? ? ? up->max_tx_count = up->port.fifosize / 4; > + > ? ? ? ?if (pdev->dev.of_node) > ? ? ? ? ? ? ? ?up->port.line = of_alias_get_id(pdev->dev.of_node, "serial"); > ? ? ? ?else > > > -- > To unsubscribe from this list: send the line "unsubscribe linux-serial" in > the body of a message to majordomo at vger.kernel.org > More majordomo info at ?http://vger.kernel.org/majordomo-info.html