Commit bd8cad85 authored by Andy Shevchenko's avatar Andy Shevchenko Committed by Greg Kroah-Hartman
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serial: 8250_dw: Comment possible corner cases in serial_out() implementation 



8250 DesignWare driver uses a few custom implementations of the serial_out().
These implementations are carefully made to avoid infinite loops. But this is
not obvious from looking at the code. Comment the possible corner cases in
the respective functions.

Signed-off-by: default avatarAndy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://lore.kernel.org/r/20250317094021.1201512-1-andriy.shevchenko@linux.intel.com


Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent 067e9585

drivers/tty/serial/8250/8250_dw.c

+17 −0
Original line number Diff line number Diff line
@@ -107,11 +107,23 @@ static inline int dw8250_modify_msr(struct uart_port *p, int offset, int value) 
	return value;

}



/*

 * This function is being called as part of the uart_port::serial_out()

 * routine. Hence, it must not call serial_port_out() or serial_out()

 * against the modified registers here, i.e. LCR.

 */

static void dw8250_force_idle(struct uart_port *p)

{

	struct uart_8250_port *up = up_to_u8250p(p);

	unsigned int lsr;



	/*

	 * The following call currently performs serial_out()

	 * against the FCR register. Because it differs to LCR

	 * there will be no infinite loop, but if it ever gets

	 * modified, we might need a new custom version of it

	 * that avoids infinite recursion.

	 */

	serial8250_clear_and_reinit_fifos(up);



	/*
@@ -128,6 +140,11 @@ static void dw8250_force_idle(struct uart_port *p) 
	serial_port_in(p, UART_RX);

}



/*

 * This function is being called as part of the uart_port::serial_out()

 * routine. Hence, it must not call serial_port_out() or serial_out()

 * against the modified registers here, i.e. LCR.

 */

static void dw8250_check_lcr(struct uart_port *p, int offset, int value)

{

	struct dw8250_data *d = to_dw8250_data(p->private_data);