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    Subject[PATCH AUTOSEL 5.12 066/160] pinctrl: mcp23s08: fix race condition in irq handler
    Date
    From: Radim Pavlik <radim.pavlik@tbs-biometrics.com>

    [ Upstream commit 897120d41e7afd9da435cb00041a142aeeb53c07 ]

    Checking value of MCP_INTF in mcp23s08_irq suggests that the handler may be
    called even when there is no interrupt pending.

    But the actual interrupt could happened between reading MCP_INTF and MCP_GPIO.
    In this situation we got nothing from MCP_INTF, but the event gets acknowledged
    on the expander by reading MCP_GPIO. This leads to losing events.

    Fix the problem by not reading any register until we see something in MCP_INTF.

    The error was reproduced and fix tested on MCP23017.

    Signed-off-by: Radim Pavlik <radim.pavlik@tbs-biometrics.com>
    Link: https://lore.kernel.org/r/AM7PR06MB6769E1183F68DEBB252F665ABA3E9@AM7PR06MB6769.eurprd06.prod.outlook.com
    Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    drivers/pinctrl/pinctrl-mcp23s08.c | 10 +++++-----
    1 file changed, 5 insertions(+), 5 deletions(-)

    diff --git a/drivers/pinctrl/pinctrl-mcp23s08.c b/drivers/pinctrl/pinctrl-mcp23s08.c
    index ce2d8014b7e0..799d596a1a4b 100644
    --- a/drivers/pinctrl/pinctrl-mcp23s08.c
    +++ b/drivers/pinctrl/pinctrl-mcp23s08.c
    @@ -351,6 +351,11 @@ static irqreturn_t mcp23s08_irq(int irq, void *data)
    if (mcp_read(mcp, MCP_INTF, &intf))
    goto unlock;

    + if (intf == 0) {
    + /* There is no interrupt pending */
    + return IRQ_HANDLED;
    + }
    +
    if (mcp_read(mcp, MCP_INTCAP, &intcap))
    goto unlock;

    @@ -368,11 +373,6 @@ static irqreturn_t mcp23s08_irq(int irq, void *data)
    mcp->cached_gpio = gpio;
    mutex_unlock(&mcp->lock);

    - if (intf == 0) {
    - /* There is no interrupt pending */
    - return IRQ_HANDLED;
    - }
    -
    dev_dbg(mcp->chip.parent,
    "intcap 0x%04X intf 0x%04X gpio_orig 0x%04X gpio 0x%04X\n",
    intcap, intf, gpio_orig, gpio);
    --
    2.30.2
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