From 21fe5dd4ccc9389f3e0ed5d32ccf696b5e641b3b Mon Sep 17 00:00:00 2001
From: "rick.chan" <chenyang@autoai.com>
Date: Fri, 24 Jul 2020 15:29:27 +0800
Subject: [PATCH] =?UTF-8?q?=E5=A2=9E=E5=8A=A0=20Linux=20id=5Ftable=20?=
 =?UTF-8?q?=E4=B8=8E=20of=5Fmatch=5Ftable.?=
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Signed-off-by: rick.chan <chenyang@autoai.com>
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 .../Linux_id_table_与_of_match_table.md       | 55 +++++++++++++++++++
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 create mode 100644 Software/Development/OperatingSystem/Linux/Kernel/Modules/DeviceTree/Linux_id_table_与_of_match_table.md

diff --git a/Software/Development/OperatingSystem/Linux/Kernel/Modules/DeviceTree/Linux_id_table_与_of_match_table.md b/Software/Development/OperatingSystem/Linux/Kernel/Modules/DeviceTree/Linux_id_table_与_of_match_table.md
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+# Linux id_table 与 of_match_table
+
+I’m currently trying to understand how linux drivers work. As far as I know, A driver’s probe/init function is called when the kernel parses the corresponding .compatible string in the device tree. However, in the arizona-spi driver it looks like there are multiple compatible strings referenced in different members:
+
+```cpp
+static const struct spi_device_id arizona_spi_ids[] = {
+{ "wm5102", WM5102 },
+{ "wm5110", WM5110 },
+{ },
+};
+MODULE_DEVICE_TABLE(spi, arizona_spi_ids);
+
+static struct spi_driver arizona_spi_driver = {
+.driver = {
+    .name   = "arizona",
+    .owner  = THIS_MODULE,
+    .pm = &arizona_pm_ops,
+
+    // Contains e.g. "wlf,wm5102"
+    .of_match_table = of_match_ptr(arizona_of_match),
+
+},
+.probe      = arizona_spi_probe,
+.remove     = arizona_spi_remove,
+.id_table   = arizona_spi_ids,                  // Contains "wm5102" and "wm5110"
+};
+```
+
+So what is the difference between arizona_spi_driver.id_table and arizona_spi_driver.driver.of_match_table?
+
+There are several mechanism for driver matching. The id_table is intended to be used for finding a match from stripped device-tree entries (without vendor part), while of_match_table is used to find a match from full device-tree entries (the ones with vendor part).
+
+If you check, arizona_of_match is defined as this:
+
+```cpp
+const struct of_device_id arizona_of_match[] = {
+    { .compatible = "wlf,wm5102", .data = (void *)WM5102 },
+    { .compatible = "wlf,wm5110", .data = (void *)WM5110 },
+    { .compatible = "wlf,wm8280", .data = (void *)WM8280 },
+    { .compatible = "wlf,wm8997", .data = (void *)WM8997 },
+    {},
+};
+```
+
+'wlf' is the vendor part for this case, while arizona_spi_ids doesn’t contain the vendor part.
+
+Hence, if you have something like this in your device tree:
+
+```cpp
+compatible = "myvendor,wm5102"
+```
+
+Your device will match against id_table but not against of_match_table since the vendor is different.
+
+The kernel will do matching against of_match_table first before check id_table (seespi_get_device_id in here). The device matching priority is: of_match_table > acpi_driver > id_table.