Hi, On 04/10/22 7:15 pm, Bin Liu wrote: > Hi, > > On Mon, Oct 03, 2022 at 09:42:24PM +0200, Lukas Wunner wrote: >> On Mon, Oct 03, 2022 at 10:10:59AM -0500, Bin Liu wrote: >>> On Tue, Sep 27, 2022 at 02:10:01PM +0200, Lukas Wunner wrote: >>>> 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 >> [...] >>>> - if (up->port.rs485.flags & SER_RS485_ENABLED) >>>> + if (priv->habit & UART_HAS_NATIVE_RS485) >>>> + serial_out(up, UART_OMAP_MDR3, priv->mdr3); >>> >>> This makes the NATIVE_RS485 always used if the SoC supports it, but >>> >>>> + else if (up->port.rs485.flags & SER_RS485_ENABLED) >>>> serial8250_em485_stop_tx(up); >>> >>> there are cases em485 should be used even if SoC supports NATIVE_RS485. >>> For example: >>> - the design has pinmux conflict and the RTS pin has to be used for >>> something else. Then a GPIO pin would be used for RS485 DE control; >>> - the design requires customized delay_rts_before_send or >>> delay_rts_after_send which NATIVE_RS485 doesn't support; >>> >>> So we might need an option for such usecases. A device tree flag? >> >> I expect those cases to be rare, hence do not see the need to > > Maybe rare, but I know some projects use GPIO for DE control. > >> address them right from the start. Support for falling back > > So I think missing it is a regression, because this patch forces to > use the RTS pin for DE control, this breaks the existing projects which > use GPIO for RTS/DE or have customized delay_rts_{before,after}_send. I agree with Bin. This patch as such can break DTs which intend to use GPIO based DE. Quick fix would be to simply look for presence of rts-gpios property in DT, if so fallback to registering serial8250_em485_*. This should avoid regressing DTs using GPIO for DE control. Regards Vignesh
