Commit 883c5a2b authored by Ilpo Järvinen's avatar Ilpo Järvinen Committed by Greg Kroah-Hartman
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serial: 8250_dw: Rework dw8250_handle_irq() locking and IIR handling 



dw8250_handle_irq() takes port's lock multiple times with no good
reason to release it in between and calls serial8250_handle_irq()
that also takes port's lock.

Take port's lock only once in dw8250_handle_irq() and use
serial8250_handle_irq_locked() to avoid releasing port's lock in
between.

As IIR_NO_INT check in serial8250_handle_irq() was outside of port's
lock, it has to be done already in dw8250_handle_irq().

DW UART can, in addition to IIR_NO_INT, report BUSY_DETECT (0x7) which
collided with the IIR_NO_INT (0x1) check in serial8250_handle_irq()
(because & is used instead of ==) meaning that no other work is done by
serial8250_handle_irq() during an BUSY_DETECT interrupt.

This allows reorganizing code in dw8250_handle_irq() to do both
IIR_NO_INT and BUSY_DETECT handling right at the start simplifying
the logic.

Tested-by: default avatarBandal, Shankar <shankar.bandal@intel.com>
Tested-by: default avatarMurthy, Shanth <shanth.murthy@intel.com>
Cc: stable <stable@kernel.org>
Reviewed-by: default avatarAndy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: default avatarIlpo Järvinen <ilpo.jarvinen@linux.intel.com>
Link: https://patch.msgid.link/20260203171049.4353-5-ilpo.jarvinen@linux.intel.com


Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent 8324a54f

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

+21 −16
Original line number Diff line number Diff line
@@ -9,6 +9,9 @@ 
 * LCR is written whilst busy.  If it is, then a busy detect interrupt is

 * raised, the LCR needs to be rewritten and the uart status register read.

 */

#include <linux/bitfield.h>

#include <linux/bits.h>

#include <linux/cleanup.h>

#include <linux/clk.h>

#include <linux/delay.h>

#include <linux/device.h>
@@ -40,6 +43,8 @@ 
#define RZN1_UART_RDMACR 0x110 /* DMA Control Register Receive Mode */



/* DesignWare specific register fields */

#define DW_UART_IIR_IID			GENMASK(3, 0)



#define DW_UART_MCR_SIRE		BIT(6)



/* Renesas specific register fields */
@@ -312,7 +317,19 @@ static int dw8250_handle_irq(struct uart_port *p) 
	bool rx_timeout = (iir & 0x3f) == UART_IIR_RX_TIMEOUT;

	unsigned int quirks = d->pdata->quirks;

	unsigned int status;

	unsigned long flags;



	switch (FIELD_GET(DW_UART_IIR_IID, iir)) {

	case UART_IIR_NO_INT:

		return 0;



	case UART_IIR_BUSY:

		/* Clear the USR */

		serial_port_in(p, d->pdata->usr_reg);



		return 1;

	}



	guard(uart_port_lock_irqsave)(p);



	/*

	 * There are ways to get Designware-based UARTs into a state where
@@ -325,20 +342,15 @@ static int dw8250_handle_irq(struct uart_port *p) 
	 * so we limit the workaround only to non-DMA mode.

	 */

	if (!up->dma && rx_timeout) {

		uart_port_lock_irqsave(p, &flags);

		status = serial_lsr_in(up);



		if (!(status & (UART_LSR_DR | UART_LSR_BI)))

			serial_port_in(p, UART_RX);



		uart_port_unlock_irqrestore(p, flags);

	}



	/* Manually stop the Rx DMA transfer when acting as flow controller */

	if (quirks & DW_UART_QUIRK_IS_DMA_FC && up->dma && up->dma->rx_running && rx_timeout) {

		uart_port_lock_irqsave(p, &flags);

		status = serial_lsr_in(up);

		uart_port_unlock_irqrestore(p, flags);



		if (status & (UART_LSR_DR | UART_LSR_BI)) {

			dw8250_writel_ext(p, RZN1_UART_RDMACR, 0);
@@ -346,19 +358,11 @@ static int dw8250_handle_irq(struct uart_port *p) 
		}

	}



	if (serial8250_handle_irq(p, iir))

		return 1;



	if ((iir & UART_IIR_BUSY) == UART_IIR_BUSY) {

		/* Clear the USR */

		serial_port_in(p, d->pdata->usr_reg);

	serial8250_handle_irq_locked(p, iir);



	return 1;

}



	return 0;

}



static void dw8250_clk_work_cb(struct work_struct *work)

{

	struct dw8250_data *d = work_to_dw8250_data(work);
@@ -867,6 +871,7 @@ static struct platform_driver dw8250_platform_driver = { 


module_platform_driver(dw8250_platform_driver);



MODULE_IMPORT_NS("SERIAL_8250");

MODULE_AUTHOR("Jamie Iles");

MODULE_LICENSE("GPL");

MODULE_DESCRIPTION("Synopsys DesignWare 8250 serial port driver");