tty: rp2: Fix reset with non forgiving PCIe host bridges

commit f16dd10ba342c429b1e36ada545fb36d4d1f0e63 upstream.

The write to RP2_GLOBAL_CMD followed by an immediate read of
RP2_GLOBAL_CMD in rp2_reset_asic() is intented to flush out the write,
however by then the device is already in reset and cannot respond to a
memory cycle access.

On platforms such as the Raspberry Pi 4 and others using the
pcie-brcmstb.c driver, any memory access to a device that cannot respond
is met with a fatal system error, rather than being substituted with all
1s as is usually the case on PC platforms.

Swapping the delay and the read ensures that the device has finished
resetting before we attempt to read from it.

Fixes: 7d9f49afa451 ("serial: rp2: New driver for Comtrol RocketPort 2 cards")
Cc: stable <stable@kernel.org>
Suggested-by: Jim Quinlan <james.quinlan@broadcom.com>
Signed-off-by: Florian Fainelli <florian.fainelli@broadcom.com>
Link: https://lore.kernel.org/r/20240906225435.707837-1-florian.fainelli@broadcom.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/tty/serial/rp2.c b/drivers/tty/serial/rp2.c
index de220ac8ca549420df1470ad4361557176357f9a..5a1de6044b38cc300140627acc6c9e7998977017 100644 (file)
--- a/drivers/tty/serial/rp2.c
+++ b/drivers/tty/serial/rp2.c
@@ -578,8 +578,8 @@ static void rp2_reset_asic(struct rp2_card *card, unsigned int asic_id)
        u32 clk_cfg;
 
        writew(1, base + RP2_GLOBAL_CMD);
-       readw(base + RP2_GLOBAL_CMD);
        msleep(100);
+       readw(base + RP2_GLOBAL_CMD);
        writel(0, base + RP2_CLK_PRESCALER);
 
        /* TDM clock configuration */