Re: [PATCH v3 2/2] serial: 8250_of: add Microchip Core16550

[sashiko-bot@kernel.org]

> From: Kohei Otsuka <kohei@spacemachines.com>
> 
> Core16550, a 16550-compatible UART for Microchip FPGAs, interrupts on
> THRE but not on TEMT. When the last character moves from the FIFO into
> the shift register, the THRE interrupt calls __stop_tx(), which finds
> TEMT clear and, without UART_CAP_NOTEMT, returns to wait for a TEMT
> interrupt that never comes. RTS, and with it the RS-485 driver enable,
> then stays asserted after the frame, and receive interrupts, disabled
> for the half-duplex transmission, stay off.
> 
> Match "microchip,core16550-rtl-v3" as a PORT_16550A, and set
> UART_CAP_NOTEMT for it, so em485 drops RTS from its stop timer one
> frame time (plus 1/7) after THRE, as it does for DesignWare UARTs.
> 
> Set UART_CAP_FIFO as well: with the capabilities already non-zero,
> serial8250_do_startup() no longer fills in the PORT_16550A default,
> and without UART_CAP_FIFO serial8250_clear_fifos() does nothing, so
> the RX FIFO is not flushed at the end of a half-duplex transmission.
> 
> Link: https://github.com/linux4microchip/meta-mchp/issues/5
> Signed-off-by: Kohei Otsuka <kohei@spacemachines.com>

Sashiko has reviewed this patch and found no issues.

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Sashiko AI review · https://sashiko.dev/#/patchset/20261110-core16550-rs485-v3-0-4294334243fa@spacemachines.com?part=2