Re: [PATCH 2/2 v5] tty/serial/8250: use mctrl_gpio helpers

[Stefan Roese]

On 11.06.19 14:44, Andy Shevchenko wrote:
On Tue, Jun 11, 2019 at 12:56:03PM +0200, Stefan Roese wrote:
From: Yegor Yefremov <yegorsli...@googlemail.com>
This patch permits the usage for GPIOs to control
the CTS/RTS/DTR/DSR/DCD/RI signals.

  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)?
 
+       if (up->gpios == 0)

This is type inconsistency with this check as far as I understand.
I guess you have to do either (up->gpios == NULL), or (!up->gpios).

Ah, right. Thanks for spotting.

Thanks,
Stefan