On Thu, Oct 06, 2022 at 12:37:43PM +0530, Vignesh Raghavendra wrote: > On 04/10/22 7:15 pm, Bin Liu wrote: > > 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. I've updated the patch to check for mctrl_gpio_to_gpiod(up->gpios, UART_GPIO_RTS) as well as user-requested delays that exceed the fixed hardware delays. The driver falls back to software emulation in that case. Updated patch is on this development branch and is currently being compile-tested by Intel's 0-day bot: https://github.com/l1k/linux/commits/rs485_sitara Thanks, Lukas
