[PATCH v2 16/16] serial: sc16is7xx: refactor EFR lock
From: Hugo Villeneuve
Date: Thu Dec 21 2023 - 18:22:55 EST
From: Hugo Villeneuve <hvilleneuve@xxxxxxxxxxxx>
Move common code for EFR lock/unlock of mutex into functions for code reuse
and clarity.
With the addition of old_lcr, move irda_mode within struct sc16is7xx_one to
reduce memory usage:
Before: /* size: 752, cachelines: 12, members: 10 */
After: /* size: 744, cachelines: 12, members: 10 */
Signed-off-by: Hugo Villeneuve <hvilleneuve@xxxxxxxxxxxx>
---
drivers/tty/serial/sc16is7xx.c | 106 ++++++++++++++++++---------------
1 file changed, 57 insertions(+), 49 deletions(-)
diff --git a/drivers/tty/serial/sc16is7xx.c b/drivers/tty/serial/sc16is7xx.c
index 15a46c164821..929206a9a6e1 100644
--- a/drivers/tty/serial/sc16is7xx.c
+++ b/drivers/tty/serial/sc16is7xx.c
@@ -330,8 +330,9 @@ struct sc16is7xx_one {
struct kthread_work reg_work;
struct kthread_delayed_work ms_work;
struct sc16is7xx_one_config config;
- bool irda_mode;
unsigned int old_mctrl;
+ u8 old_lcr; /* Value before EFR access. */
+ bool irda_mode;
};
struct sc16is7xx_port {
@@ -412,6 +413,49 @@ static void sc16is7xx_power(struct uart_port *port, int on)
on ? 0 : SC16IS7XX_IER_SLEEP_BIT);
}
+/*
+ * In an amazing feat of design, the Enhanced Features Register (EFR)
+ * shares the address of the Interrupt Identification Register (IIR).
+ * Access to EFR is switched on by writing a magic value (0xbf) to the
+ * Line Control Register (LCR). Any interrupt firing during this time will
+ * see the EFR where it expects the IIR to be, leading to
+ * "Unexpected interrupt" messages.
+ *
+ * Prevent this possibility by claiming a mutex while accessing the EFR,
+ * and claiming the same mutex from within the interrupt handler. This is
+ * similar to disabling the interrupt, but that doesn't work because the
+ * bulk of the interrupt processing is run as a workqueue job in thread
+ * context.
+ */
+static void sc16is7xx_efr_lock(struct uart_port *port)
+{
+ struct sc16is7xx_one *one = to_sc16is7xx_one(port, port);
+
+ mutex_lock(&one->efr_lock);
+
+ /* Backup content of LCR. */
+ one->old_lcr = sc16is7xx_port_read(port, SC16IS7XX_LCR_REG);
+
+ /* Enable access to Enhanced register set */
+ sc16is7xx_port_write(port, SC16IS7XX_LCR_REG, SC16IS7XX_LCR_CONF_MODE_B);
+
+ /* Disable cache updates when writing to EFR registers */
+ regcache_cache_bypass(one->regmap, true);
+}
+
+static void sc16is7xx_efr_unlock(struct uart_port *port)
+{
+ struct sc16is7xx_one *one = to_sc16is7xx_one(port, port);
+
+ /* Re-enable cache updates when writing to normal registers */
+ regcache_cache_bypass(one->regmap, false);
+
+ /* Restore original content of LCR */
+ sc16is7xx_port_write(port, SC16IS7XX_LCR_REG, one->old_lcr);
+
+ mutex_unlock(&one->efr_lock);
+}
+
static void sc16is7xx_ier_clear(struct uart_port *port, u8 bit)
{
struct sc16is7xx_port *s = dev_get_drvdata(port->dev);
@@ -522,45 +566,19 @@ static int sc16is7xx_set_baud(struct uart_port *port, int baud)
div /= 4;
}
- /* In an amazing feat of design, the Enhanced Features Register shares
- * the address of the Interrupt Identification Register, and is
- * switched in by writing a magic value (0xbf) to the Line Control
- * Register. Any interrupt firing during this time will see the EFR
- * where it expects the IIR to be, leading to "Unexpected interrupt"
- * messages.
- *
- * Prevent this possibility by claiming a mutex while accessing the
- * EFR, and claiming the same mutex from within the interrupt handler.
- * This is similar to disabling the interrupt, but that doesn't work
- * because the bulk of the interrupt processing is run as a workqueue
- * job in thread context.
- */
- mutex_lock(&one->efr_lock);
-
- lcr = sc16is7xx_port_read(port, SC16IS7XX_LCR_REG);
-
- /* Open the LCR divisors for configuration */
- sc16is7xx_port_write(port, SC16IS7XX_LCR_REG,
- SC16IS7XX_LCR_CONF_MODE_B);
-
/* Enable enhanced features */
- regcache_cache_bypass(one->regmap, true);
+ sc16is7xx_efr_lock(port);
sc16is7xx_port_update(port, SC16IS7XX_EFR_REG,
SC16IS7XX_EFR_ENABLE_BIT,
SC16IS7XX_EFR_ENABLE_BIT);
-
- regcache_cache_bypass(one->regmap, false);
-
- /* Put LCR back to the normal mode */
- sc16is7xx_port_write(port, SC16IS7XX_LCR_REG, lcr);
-
- mutex_unlock(&one->efr_lock);
+ sc16is7xx_efr_unlock(port);
sc16is7xx_port_update(port, SC16IS7XX_MCR_REG,
SC16IS7XX_MCR_CLKSEL_BIT,
prescaler);
- /* Open the LCR divisors for configuration */
+ /* Backup LCR and access special register set (DLL/DLH) */
+ lcr = sc16is7xx_port_read(port, SC16IS7XX_LCR_REG);
sc16is7xx_port_write(port, SC16IS7XX_LCR_REG,
SC16IS7XX_LCR_CONF_MODE_A);
@@ -570,7 +588,7 @@ static int sc16is7xx_set_baud(struct uart_port *port, int baud)
sc16is7xx_port_write(port, SC16IS7XX_DLL_REG, div % 256);
regcache_cache_bypass(one->regmap, false);
- /* Put LCR back to the normal mode */
+ /* Restore LCR and access to general register set */
sc16is7xx_port_write(port, SC16IS7XX_LCR_REG, lcr);
return DIV_ROUND_CLOSEST(clk / 16, div);
@@ -1049,17 +1067,7 @@ static void sc16is7xx_set_termios(struct uart_port *port,
if (!(termios->c_cflag & CREAD))
port->ignore_status_mask |= SC16IS7XX_LSR_BRK_ERROR_MASK;
- /* As above, claim the mutex while accessing the EFR. */
- mutex_lock(&one->efr_lock);
-
- sc16is7xx_port_write(port, SC16IS7XX_LCR_REG,
- SC16IS7XX_LCR_CONF_MODE_B);
-
/* Configure flow control */
- regcache_cache_bypass(one->regmap, true);
- sc16is7xx_port_write(port, SC16IS7XX_XON1_REG, termios->c_cc[VSTART]);
- sc16is7xx_port_write(port, SC16IS7XX_XOFF1_REG, termios->c_cc[VSTOP]);
-
port->status &= ~(UPSTAT_AUTOCTS | UPSTAT_AUTORTS);
if (termios->c_cflag & CRTSCTS) {
flow |= SC16IS7XX_EFR_AUTOCTS_BIT |
@@ -1071,16 +1079,16 @@ static void sc16is7xx_set_termios(struct uart_port *port,
if (termios->c_iflag & IXOFF)
flow |= SC16IS7XX_EFR_SWFLOW1_BIT;
- sc16is7xx_port_update(port,
- SC16IS7XX_EFR_REG,
- SC16IS7XX_EFR_FLOWCTRL_BITS,
- flow);
- regcache_cache_bypass(one->regmap, false);
-
/* Update LCR register */
sc16is7xx_port_write(port, SC16IS7XX_LCR_REG, lcr);
- mutex_unlock(&one->efr_lock);
+ /* Update EFR registers */
+ sc16is7xx_efr_lock(port);
+ sc16is7xx_port_write(port, SC16IS7XX_XON1_REG, termios->c_cc[VSTART]);
+ sc16is7xx_port_write(port, SC16IS7XX_XOFF1_REG, termios->c_cc[VSTOP]);
+ sc16is7xx_port_update(port, SC16IS7XX_EFR_REG,
+ SC16IS7XX_EFR_FLOWCTRL_BITS, flow);
+ sc16is7xx_efr_unlock(port);
/* Get baud rate generator configuration */
baud = uart_get_baud_rate(port, termios, old,
--
2.39.2