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The default polarity of RS485 DE signal is active high. This driver does
not handle such case properly. Currently, when a pin is multiplexed as a
UART CTS_B on boot, this pin is pulled HIGH by the i.MX UART CTS circuit,
which activates DE signal on the RS485 transceiver and thus behave as if
the RS485 was transmitting data, so the system blocks the RS485 bus when
it starts and until user application takes over. This behavior is not OK.
The problem consists of two separate parts.
First, the i.MX UART IP requires UCR1 UARTEN and UCR2 RXEN to be set for
UCR2 CTSC and CTS bits to have any effect. The UCR2 CTSC bit permits the
driver to set CTS (RTS_B or RS485 DE signal) to either level sychronous
to the internal UART IP clock. Compared to other options, like GPIO CTS
control, this has the benefit of being synchronous to the UART IP clock
and thus without glitches or bus delays. The reason for the CTS design
is likely because when the Receiver is disabled, the UART IP can never
indicate that it is ready to receive data by assering CTS signal, so
the CTS is always pulled HIGH by default.
When the port is closed by user space, imx_uart_stop_rx() clears UCR2
RXEN bit, and imx_uart_shutdown() clears UCR1 UARTEN bit. This disables
UART Receiver and UART itself, and forces CTS signal HIGH, which leads
to the RS485 bus being blocked because RS485 DE is incorrectly active.
The proposed solution for this problem is to keep the Receiver running
even after the port is closed, but in loopback mode. This disconnects
the RX FIFO input from the RXD external signal, and since UCR2 TXEN is
cleared, the UART Transmitter is disabled, so nothing can feed data in
the RX FIFO. Because the Receiver is still enabled, the UCR2 CTSC and
CTS bits still have effect and the CTS (RS485 DE) control is retained.
Note that in case of RS485 DE signal active low, there is no problem and
no special handling is necessary. The CTS signal defaults to HIGH, thus
the RS485 is by default set to Receive and the bus is not blocked.
Note that while there is the possibility to control CTS using GPIO with
either CTS polarity, this has the downside of not being synchronous to
the UART IP clock and thus glitchy and susceptible to slow DE switching.
Second, on boot, before the UART driver probe callback is called, the
driver core triggers pinctrl_init_done() and configures the IOMUXC to
default state. At this point, UCR1 UARTEN and UCR2 RXEN are both still
cleared, but UART CTS_B (RS485 DE) is configured as CTS function, thus
the RTS signal is pulled HIGH by the UART IP CTS circuit.
One part of the solution here is to enable UCR1 UARTEN and UCR2 RXEN and
UTS loopback in this driver probe callback, thus unblocking the CTSC and
CTS control early on. But this is still too late, since the pin control
is already configured and CTS has been pulled HIGH for a short period
of time.
When Linux kernel boots and this driver is bound, the pin control is set
to special "init" state if the state is available, and driver can switch
the "default" state afterward when ready. This state can be used to set
the CTS line as a GPIO in DT temporarily, and a GPIO hog can force such
GPIO to LOW, thus keeping the RS485 DE line LOW early on boot. Once the
driver takes over and UCR1 UARTEN and UCR2 RXEN and UTS loopback are all
enabled, the driver can switch to "default" pin control state and control
the CTS line as function instead. DT binding example is below:
"
&gpio6 {
rts-init-hog {
gpio-hog;
gpios = <5 0>;
output-low;
line-name = "rs485-de";
};
};
&uart5 { /* DHCOM UART2 */
pinctrl-0 = <&pinctrl_uart5>;
pinctrl-1 = <&pinctrl_uart5_init>;
pinctrl-names = "default", "init";
...
};
pinctrl_uart5_init: uart5-init-grp {
fsl,pins = <
...
MX6QDL_PAD_CSI0_DAT19__GPIO6_IO05 0x30b1
>;
};
pinctrl_uart5: uart5-grp {
fsl,pins = <
...
MX6QDL_PAD_CSI0_DAT19__UART5_CTS_B 0x30b1
>;
};
"
Tested-by: Christoph Niedermaier <cniedermaier@dh-electronics.com>
Reviewed-by: Fabio Estevam <festevam@denx.de>
Signed-off-by: Marek Vasut <marex@denx.de>
Link: https://lore.kernel.org/r/20220929144400.13571-1-marex@denx.de
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
JZ4750/55/60 (but not JZ4760b) have an optional /2 divider between the
EXT oscillator and some peripherals including UART, which will
be enabled if using a 24 MHz oscillator, and disabled when
using a 12 MHz oscillator.
This behavior relies on hardware differences: most boards (if not all)
with those SoCs have 12 or 24 MHz oscillators but many peripherals want
12Mhz to operate properly (AIC and USB-PHY at least).
The 16MHz threshold looks arbitrary but used in vendor's bootloader code
for enable the divider.
The patch doesn't affect JZ4760's behavior as it is subject for another
patchset with re-classification of all supported ingenic UARTs.
Link: https://github.com/carlos-wong/uboot_jz4755/blob/master/cpu/mips/jz_serial.c#L158
Signed-off-by: Siarhei Volkau <lis8215@gmail.com>
Link: https://lore.kernel.org/r/20221031184041.1338129-3-lis8215@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Read the DMA status before terminating the DMA, as doing so deletes
the DMA desc.
Also, to get the correct transfer status information, pause the DMA
using dmaengine_pause() before reading the DMA status.
Fixes: e9ea096dd225 ("serial: tegra: add serial driver")
Reviewed-by: Jon Hunter <jonathanh@nvidia.com>
Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Acked-by: Thierry Reding <treding@nvidia.com>
Signed-off-by: Akhil R <akhilrajeev@nvidia.com>
Signed-off-by: Kartik <kkartik@nvidia.com>
Link: https://lore.kernel.org/r/1666105086-17326-1-git-send-email-kkartik@nvidia.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Take advantage of the new uart_xmit_advance() helper.
Reviewed-by: Baolin Wang <baolin.wang@linux.alibaba.com>
Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Link: https://lore.kernel.org/r/20221019091151.6692-34-ilpo.jarvinen@linux.intel.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Take advantage of the new uart_xmit_advance() helper.
Reviewed-by: Sam Protsenko <semen.protsenko@linaro.org>
Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Link: https://lore.kernel.org/r/20221019091151.6692-29-ilpo.jarvinen@linux.intel.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Take advantage of the new uart_xmit_advance() helper.
Acked-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Acked-by: Neil Armstrong <neil.armstrong@linaro.org>
Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Link: https://lore.kernel.org/r/20221019091151.6692-23-ilpo.jarvinen@linux.intel.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Take advantage of the new uart_xmit_advance() helper.
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Link: https://lore.kernel.org/r/20221019091151.6692-22-ilpo.jarvinen@linux.intel.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Take advantage of the new uart_xmit_advance() helper.
Reviewed-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Link: https://lore.kernel.org/r/20221019091151.6692-18-ilpo.jarvinen@linux.intel.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Take advantage of the new uart_xmit_advance() helper.
Reviewed-by: Claudiu Beznea <claudiu.beznea@microchip.com>
Acked-By: Richard GENOUD <richard.genoud@gmail.com>
Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Link: https://lore.kernel.org/r/20221019091151.6692-12-ilpo.jarvinen@linux.intel.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Take advantage of the new uart_xmit_advance() helper.
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Link: https://lore.kernel.org/r/20221019091151.6692-8-ilpo.jarvinen@linux.intel.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Take advantage of the new uart_xmit_advance() helper.
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Link: https://lore.kernel.org/r/20221019091151.6692-6-ilpo.jarvinen@linux.intel.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Take advantage of the new uart_xmit_advance() helper.
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Link: https://lore.kernel.org/r/20221019091151.6692-5-ilpo.jarvinen@linux.intel.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Recent TI Sitara SoCs such as AM64/AM65 have gained the ability to
automatically assert RTS when data is transmitted, obviating the need
to emulate this functionality in software.
The feature is controlled through new DIR_EN and DIR_POL bits in the
Mode Definition Register 3. For details see page 8783 and 8890 of the
AM65 TRM: https://www.ti.com/lit/ug/spruid7e/spruid7e.pdf
Cc: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Cc: Su Bao Cheng <baocheng.su@siemens.com>
Cc: Vignesh Raghavendra <vigneshr@ti.com>
Cc: Jan Kiszka <jan.kiszka@siemens.com>
Cc: Bin Liu <b-liu@ti.com>
Tested-by: Zeng Chao <chao.zeng@siemens.com>
Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Signed-off-by: Lukas Wunner <lukas@wunner.de>
Link: https://lore.kernel.org/r/e9f25f5c9200a35d3162973c2b45d6b892cc9bf2.1665906869.git.lukas@wunner.de
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Added changes to support the hibernation feature for serial UART.
Added support for freeze, restore and thaw callbacks to put the
device into hibernation.
Signed-off-by: Aniket Randive <quic_arandive@quicinc.com>
Link: https://lore.kernel.org/r/1665123780-20557-1-git-send-email-quic_arandive@quicinc.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
uart_port_tx_limited() is a new helper to send characters to the device.
Use it in these drivers.
mux.c also needs to define tx_done(). But I'm not sure if the driver
really wants to wait for all the characters to dismiss from the HW fifo
at this code point. Hence I marked this as FIXME.
Cc: Russell King <linux@armlinux.org.uk>
Cc: Florian Fainelli <f.fainelli@gmail.com>
Cc: bcm-kernel-feedback-list@broadcom.com
Cc: "Pali Rohár" <pali@kernel.org>
Cc: Kevin Cernekee <cernekee@gmail.com>
Cc: Palmer Dabbelt <palmer@dabbelt.com>
Cc: Paul Walmsley <paul.walmsley@sifive.com>
Cc: Orson Zhai <orsonzhai@gmail.com>
Cc: Baolin Wang <baolin.wang7@gmail.com>
Cc: Chunyan Zhang <zhang.lyra@gmail.com>
Cc: Patrice Chotard <patrice.chotard@foss.st.com>
Cc: linux-riscv@lists.infradead.org
Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Signed-off-by: Jiri Slaby (SUSE) <jirislaby@kernel.org>
Link: https://lore.kernel.org/r/20221004104927.14361-4-jirislaby@kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
