linux-kernel - Re: [PATCH v2 1/2] dt-bindings: google,cros-ec-keyb: Introduce switches only compatible

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Date:   Thu, 12 May 2022 13:11:39 -0700
From:   Stephen Boyd <swboyd@...omium.org>
To:     Dmitry Torokhov <dmitry.torokhov@...il.com>
Cc:     Doug Anderson <dianders@...omium.org>,
        LKML <linux-kernel@...r.kernel.org>, patches@...ts.linux.dev,
        chrome-platform@...ts.linux.dev,
        Krzysztof Kozlowski <krzk@...nel.org>,
        Rob Herring <robh+dt@...nel.org>, devicetree@...r.kernel.org,
        Benson Leung <bleung@...omium.org>,
        Guenter Roeck <groeck@...omium.org>,
        Hsin-Yi Wang <hsinyi@...omium.org>,
        "Joseph S. Barrera III" <joebar@...omium.org>
Subject: Re: [PATCH v2 1/2] dt-bindings: google,cros-ec-keyb: Introduce
 switches only compatible

Quoting Stephen Boyd (2022-05-12 11:58:02)
> Quoting Dmitry Torokhov (2022-05-12 03:22:30)
> >
> > Have we solved module loading in the presence of multiple compatibles?
> > IIRC we only ever try to load module on the first compatible, so you'd
> > be breaking autoloading cros-ec-keyb on these older kernels. I think the
> > cure that is being proposed is worse than the disease.
> >
>
> The first compatible is still cros-ec-keyb in the driver though? Or you
> mean the first compatible in the node? I'm not aware of this problem at
> all but I can certainly test out a fake node and module and see if it
> gets autoloaded.

I can't get this test module to fail to load no matter what I do. I
commented out the second match table entry, and kept it there and
removed 'vendor,switch-compat' from the DTS. Module still autoloads.

----8<----
diff --git a/arch/arm64/boot/dts/qcom/sc7180.dtsi
b/arch/arm64/boot/dts/qcom/sc7180.dtsi
index 42a87fa4976e..a6173b79ba67 100644
--- a/arch/arm64/boot/dts/qcom/sc7180.dtsi
+++ b/arch/arm64/boot/dts/qcom/sc7180.dtsi
@@ -54,6 +54,10 @@ aliases {
 		spi11 = &spi11;
 	};

+	mynode {
+		compatible = "vendor,switch-compat", "vendor,keyb-compat";
+	};
+
 	clocks {
 		xo_board: xo-board {
 			compatible = "fixed-clock";
diff --git a/lib/Makefile b/lib/Makefile
index a841be5244ac..0a784011feb5 100644
--- a/lib/Makefile
+++ b/lib/Makefile
@@ -74,6 +74,7 @@ UBSAN_SANITIZE_test_ubsan.o := y
 obj-$(CONFIG_TEST_KSTRTOX) += test-kstrtox.o
 obj-$(CONFIG_TEST_LIST_SORT) += test_list_sort.o
 obj-$(CONFIG_TEST_MIN_HEAP) += test_min_heap.o
+obj-m += dtmod.o
 obj-$(CONFIG_TEST_LKM) += test_module.o
 obj-$(CONFIG_TEST_VMALLOC) += test_vmalloc.o
 obj-$(CONFIG_TEST_OVERFLOW) += test_overflow.o
diff --git a/lib/dtmod.c b/lib/dtmod.c
new file mode 100644
index 000000000000..c34ae37b8ff0
--- /dev/null
+++ b/lib/dtmod.c
@@ -0,0 +1,44 @@
+// SPDX-License-Identifier: GPL-2.0-only
+
+#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
+
+#include <linux/init.h>
+#include <linux/module.h>
+#include <linux/mod_devicetable.h>
+#include <linux/platform_device.h>
+#include <linux/printk.h>
+
+static int test_probe(struct platform_device *pdev)
+{
+	dev_info(&pdev->dev, "I got probed\n");
+
+	return 0;
+}
+
+static int test_remove(struct platform_device *pdev)
+{
+	dev_info(&pdev->dev, "I got removed\n");
+
+	return 0;
+}
+
+static const struct of_device_id test_of_match[] = {
+	{ .compatible = "vendor,keyb-compat" },
+	{ .compatible = "vendor,switch-compat" }, // comment out
+	{}
+};
+MODULE_DEVICE_TABLE(of, test_of_match);
+
+static struct platform_driver test_keyb_driver = {
+	.probe = test_probe,
+	.remove = test_remove,
+	.driver = {
+		.name = "test-ec-keyb",
+		.of_match_table = test_of_match,
+	},
+};
+
+module_platform_driver(test_keyb_driver);
+
+MODULE_LICENSE("GPL v2");
+MODULE_ALIAS("platform:test-ec-keyb");