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SubjectRe: [PATCH 2/2 v5] tty/serial/8250: use mctrl_gpio helpers
On Tue, Jun 11, 2019 at 04:02:54PM +0200, Stefan Roese wrote:
> On 11.06.19 14:44, Andy Shevchenko wrote:
> > On Tue, Jun 11, 2019 at 12:56:03PM +0200, Stefan Roese wrote:

> > > static inline void serial8250_out_MCR(struct uart_8250_port *up, int value)
> > > {
> > > serial_out(up, UART_MCR, value);
> > > +
> > > + if (up->gpios) {
> > > + int mctrl_gpio = 0;
> > > +
> > > + if (value & UART_MCR_RTS)
> > > + mctrl_gpio |= TIOCM_RTS;
> > > + if (value & UART_MCR_DTR)
> > > + mctrl_gpio |= TIOCM_DTR;
> > > +
> > > + mctrl_gpio_set(up->gpios, mctrl_gpio);
> > > + }
> > > }

> > > static inline int serial8250_in_MCR(struct uart_8250_port *up)
> > > {
> > > - return serial_in(up, UART_MCR);
> > > + int mctrl;
> > > +
> > > + mctrl = serial_in(up, UART_MCR);
> > > +
> > > + if (up->gpios) {
> > > + int mctrl_gpio = 0;
> > > +
> > > + /* save current MCR values */
> > > + if (mctrl & UART_MCR_RTS)
> > > + mctrl_gpio |= TIOCM_RTS;
> > > + if (mctrl & UART_MCR_DTR)
> > > + mctrl_gpio |= TIOCM_DTR;
> > > +
> > > + mctrl_gpio = mctrl_gpio_get_outputs(up->gpios, &mctrl_gpio);
> > > + if (mctrl_gpio & TIOCM_RTS)
> > > + mctrl |= UART_MCR_RTS;
> > > + else
> > > + mctrl &= ~UART_MCR_RTS;
> > > +
> > > + if (mctrl_gpio & TIOCM_DTR)
> > > + mctrl |= UART_MCR_DTR;
> > > + else
> > > + mctrl &= ~UART_MCR_DTR;
> > > + }
> > > +
> > > + return mctrl;
> > > }
> >
> > These are using OR logic with potentially volatile data. Shouldn't we mask
> > unused bits in UART_MCR in case of up->gpios != NULL?
>
> Sorry, I don't see, which bits you are referring to? Could you please be
> a bit more specific with the variable / macro meant (example)?

I meant that we double write values in the out() which might have some
consequences, though I hope nothing wrong with it happens.

In the in() we read the all bits in the register.

As now I look at the implementation of mctrl_gpio_get_outputs(),
I think we rather get helpers for conversion between TIOCM and UART_MCR values,
so, they can be used in get_mctrl() / set_mctrl() and above.

The logic now is understandable to me (I was confused by the conversions here
and there).

--
With Best Regards,
Andy Shevchenko


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