src/sys/dev/uart/uart_dev_ns8250.c, branch release/12.3.0

ns8250: don't drop IER_TXRDY on bus_grab/ungrab

2021-03-16T17:56:03Z

It has been observed that some systems are often unable to resume from ddb after entering with debug.kdb.enter=1. Checking the status further shows the terminal is blocked waiting in tty_drain(), but it never makes progress in clearing the output queue, because sc->sc_txbusy is high. I noticed that when entering polling mode for the debugger, IER_TXRDY is set in the failure case. Since this bit is never tracked by the softc, it will not be restored by ns8250_bus_ungrab(). This creates a race in which a TX interrupt can be lost, creating the hang described above. Ensuring that this bit is restored is enough to prevent this, and resume from ddb as expected. The solution is to track this bit in the sc->ier field, for the same lifetime that TX interrupts are enabled. PR: 223917, 240122 Sponsored by: The FreeBSD Foundation (cherry picked from commit 7e7f7beee732810d3afcc83828341ac3e139b5bd)

MFC 359899: Correct baud rate error calculation.

2020-09-08T22:19:06Z

Shifting right by 1 is not the same as dividing by 2 for signed values. In particular, dividing a signed value by 2 gives the integer ceiling of the (e.g. -5 / 2 == -2) whereas shifting right by 1 always gives the floor (-5 >> 1 == -3). An embedded board with a 25 Mhz base clock results in an error of -30.5% when used with a baud rate of 115200. Using division, this truncates to -30% and is permitted. Using the shift, this fails and is rejected causing TIOCSETA requests to fail with EINVAL and breaking getty(8). Using division gives the same error range for both over and under baud rates and also makes the code match the behavior documented in the existing comment about supporting boards with 25 Mhz clocks.

MFC r352369: Relax TX draining in ns8250_bus_transmit().

2019-09-29T02:55:57Z

Since TX interrupt is generated when THRE is set, wait for TEMT set means wait for full character transmission time. At low speeds that may take awhile, burning CPU time while holding sc_hwmtx lock, also congested. This is partial revert of r317659.

add snps IP uart support / genaralize UART

2018-08-19T21:10:21Z

This is an amalgam of a patch by Doug Ambrisko to generalize uart_acpi_find_device, imp moving the ACPI table to uart_dev_ns8250.c and advice by jhb to work around a bug in the EPYC 3151 BIOS (the BIOS incorrectly marks the serial ports as disabled) Reviewed by: imp MFC after: 8 weeks Differential Revision: https://reviews.freebsd.org/D16432

Add busy detect quirk to list of console options

2018-07-22T23:32:21Z

This change allows one to set the busy_detect flag required by the synopsys UART at the loader prompt. This is needed by the EPYC 3000 SoC. This will give users a working console up to the point where getty is required: hw.uart.console="mm:0xfedc9000,rs:2,bd:1" Reviewed by: imp MFC after: 4 weeks Differential Revision: https://reviews.freebsd.org/D16399

sys/dev: further adoption of SPDX licensing ID tags.

2017-11-27T14:52:40Z

Mainly focus on files that use BSD 2-Clause license, however the tool I was using misidentified many licenses so this was mostly a manual - error prone - task. The Software Package Data Exchange (SPDX) group provides a specification to make it easier for automated tools to detect and summarize well known opensource licenses. We are gradually adopting the specification, noting that the tags are considered only advisory and do not, in any way, superceed or replace the license texts.

uart: detect 256-byte FIFOs

2017-10-10T20:08:30Z

Submitted by: Zakary Nafziger Sponsored by: The FreeBSD Foundation

Make some UART consoles to not spin wait for data to be sent.

2017-05-01T19:47:10Z

At least with Tx FIFO enabled it shows me ~10% reduction of verbose boot time with serial console at 115200 baud. Reviewed by: marcel MFC after: 2 weeks

Add support for UART found in the Ingenic XBurst system on chips.

2016-11-17T14:41:22Z

These CPUs has non-standard UART enable bit hidden in the UART FIFO Control Register. Sponsored by: DARPA, AFRL

sys/dev: minor spelling fixes.

2016-05-03T03:41:25Z

Most affect comments, very few have user-visible effects.