[PATCH 1/2] mfd: intel-lpss: fall back to polling when no usable IRQ

[Samuel Tirwa <samuel.tirwa@web.de>]

On platforms such as the HONOR MagicBook Pro 14 (2025) (Intel Core Ultra 9 285H)
the firmware ACPI tables report the Intel LPSS I2C controllers' PCI INTx line as
not connected (Interrupt Line = 0xff, GSI 255) and do not grant MSI control
through _OSC.  As a result acpi_pci_irq_enable() sets dev->irq to
IRQ_NOTCONNECTED and intel_lpss_probe() rejects it, so all three I2C
controllers (8086:7778/7779/777a) fail to probe with -ENOTCONN and the
touchpad/touchscreen are never exposed.

Treat IRQ_NOTCONNECTED as 'no interrupt available' and pass 0 as the IRQ base
to the child devices instead of failing.  The DesignWare I2C driver already
supports a polling mode when no IRQ resource is present, which keeps the
controllers functional on these firmwares.

Signed-off-by: Samuel Tirwa <samuel.tirwa@web.de>
---
 drivers/mfd/intel-lpss.c | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/drivers/mfd/intel-lpss.c b/drivers/mfd/intel-lpss.c
index f71e076..f785d5d 100644
--- a/drivers/mfd/intel-lpss.c
+++ b/drivers/mfd/intel-lpss.c
@@ -1,5 +1,6 @@
 #include <linux/mfd/core.h>
 #include <linux/module.h>
+#include <linux/interrupt.h>
 
 int intel_lpss_probe(struct device *dev,
                      const struct intel_lpss_platform_info *info)
@@ -7,10 +8,17 @@ int intel_lpss_probe(struct device *dev,
 	struct intel_lpss *lpss;
 	int ret;
 
-	if (!info || !info->mem || info->irq <= 0)
+	if (!info || !info->mem)
 		return -EINVAL;
 
-	if (info->irq < 0)
+	/*
+	 * Firmware on some platforms (e.g. HONOR MagicBook Pro 14 2025)
+	 * reports the LPSS PCI INTx line as not connected (IRQ_NOTCONNECTED).
+	 * Fall back to polling mode in that case instead of failing probe.
+	 */
+	if (info->irq == IRQ_NOTCONNECTED)
+		info->irq = 0;
+	else if (info->irq < 0)
 		return info->irq;
 
 	lpss = devm_kzalloc(dev, sizeof(*lpss), GFP_KERNEL);
-- 
2.56.0.windows.4