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SubjectRe: [PATCH 1/2] serial: sh-sci: Fix early deassertion of dedicated RTS
Hi Geert,

On Monday 09 Jan 2017 10:53:55 Geert Uytterhoeven wrote:
> On Fri, Jan 6, 2017 at 1:30 PM, Laurent Pinchart wrote:
> > On Friday 02 Dec 2016 13:35:10 Geert Uytterhoeven wrote:
> >> If a UART has dedicated RTS/CTS pins, there are some issues:
> >> 1. When changing hardware control flow, the new AUTORTS state is not
> >> immediately reflected in the hardware, but only when RTS is raised.
> >> However, the serial core doesn't call .set_mctrl() after
> >> .set_termios(), hence AUTORTS may only become effective when the port
> >> is closed, and reopened later.
> >> Note that this problem does not happen when manually using stty to
> >> change CRTSCTS, as AUTORTS will work fine on next open.
> >>
> >> 2. When hardware control flow is disabled (or AUTORTS is not yet
> >> effective), changing any serial port configuration deasserts RTS, as
> >> .set_termios() calls sci_init_pins().
> >
> > Isn't this still a problem with this patch applied ? Calling
> > sci_set_mctrl() should reconfigure the pins properly, but won't there be
> > a short window during which the configuration will be wrong ?
> You mean in between the calls to sci_init_pins() and sci_set_mctrl()?

That's what I mean, yes.

> I don't think _de_asserting RTS for a few microseconds matters much, would
> it? Asserting RTS wrongly would be worse.

It's not the end of the world, but as you're trying to fix this issue, maybe
it would be a good time to refactor the code properly and fix the core problem
(.set_termios() calling sci_init_pins()) rather than working around it :-)


Laurent Pinchart

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