Re: [PATCH v2 2/2] tty: imx serial: Implement support for reversing TX and RX polarity

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On Mon, Feb 10, 2020 at 2:50 PM Uwe Kleine-König
<u.kleine-koenig@xxxxxxxxxxxxxx> wrote:
>
> Hello George,
>
> On Mon, Feb 10, 2020 at 01:29:49PM -0600, George Hilliard wrote:
> > @@ -1390,6 +1392,8 @@ static int imx_uart_startup(struct uart_port *port)
> >       ucr4 = imx_uart_readl(sport, UCR4) & ~UCR4_OREN;
> >       if (!sport->dma_is_enabled)
> >               ucr4 |= UCR4_OREN;
> > +     if (sport->inverted_rx)
> > +             ucr4 |= UCR4_INVR;
>
> You fail to clear this bit if .inverted_rx is false.

I believe this is taken care of by the SRST asserted slightly above
this - UCR* is reset by this. I see that this reset is also done in the
imx_uart_flush_buffer() implementation, but as I understand it, this
is a cleanup method that doesn't reconfigure much of the peripheral.

> >       imx_uart_writel(sport, ucr4, UCR4);
> >
> >       ucr2 = imx_uart_readl(sport, UCR2) & ~UCR2_ATEN;
> > @@ -1404,19 +1408,17 @@ static int imx_uart_startup(struct uart_port *port)
> >               ucr2 &= ~UCR2_RTSEN;
> >       imx_uart_writel(sport, ucr2, UCR2);
> >
> > +     ucr3 = imx_uart_readl(sport, UCR3);
> > +     if (sport->inverted_tx)
> > +             ucr3 |= UCR3_INVT;
>
> Also I think setting this bit here is a bit late because UCR2_TXEN was
> already set so changing UCR3_INVT probably results in a spike?!

Good point here; this should indeed be done before TX start.

George




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