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Platform Device Model
Purpose
Explain the Linux driver model for platform (and similar) buses: struct device, device_driver, probe/remove, resource acquisition, sysfs, and deferred probe — the glue between device tree and driver code.
When to Use
- Implementing or debugging
platform_driverlifecycle - Exposing driver state via sysfs
- Understanding uevent /
udevdevice node creation - Before
skills/kernel-dev/writing-char-drivers
Workflow
1. Object hierarchy
bus_type (platform, amba, pci, i2c, spi)
├── struct device — hardware instance
└── struct device_driver — driver logic
└── probe(dev) / remove(dev)Platform devices often come from DT (of_platform) or legacy board files.
2. Platform driver skeleton
c
static int my_probe(struct platform_device *pdev)
{
struct resource *res;
void __iomem *base;
res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
base = devm_ioremap_resource(&pdev->dev, res);
if (IS_ERR(base))
return PTR_ERR(base);
platform_set_drvdata(pdev, priv);
return 0;
}
static void my_remove(struct platform_device *pdev)
{
/* devm_* auto-cleanup on remove */
}
static struct platform_driver my_pdrv = {
.probe = my_probe,
.remove = my_remove,
.driver = {
.name = "my-dev",
.of_match_table = my_of_match,
},
};
module_platform_driver(my_pdrv);Prefer devm_* helpers for automatic unwind.
3. Device properties (DT / ACPI)
c
u32 speed;
device_property_read_u32(&pdev->dev, "clock-speed", &speed);
bool flag = device_property_present(&pdev->dev, "feature-x");4. Sysfs (driver visibility)
c
static ssize_t status_show(struct device *dev,
struct device_attribute *attr, char *buf)
{
return sysfs_emit(buf, "ok\n");
}
static DEVICE_ATTR_RO(status);
/* in probe */
device_create_file(&pdev->dev, &dev_attr_status);5. Deferred probe
Return -EPROBE_DEFER when a clock, regulator, or bus is not ready — core retries later.
6. Debug
bash
ls /sys/bus/platform/devices/
ls /sys/bus/platform/drivers/
cat /sys/kernel/debug/devices_deferred # if debugfs enabled
udevadm monitor7. Agent usage
/platform-device-model Convert legacy board file driver to DT platform_driver with devm_ioremapCommon Problems
| Symptom | Cause | Fix |
|---|---|---|
-EBUSY on probe | Resource claimed twice | Check status / duplicate nodes |
No /dev node | Char device not registered | See writing-char-drivers |
| Deferred forever | Supplier driver missing | Fix DT dependency chain |
| Remove crash | Manual free vs devm mismatch | Use devm consistently |
| Name mismatch | .name vs compatible | OF uses of_match_table |
Related Skills
skills/kernel-dev/device-tree— hardware descriptionskills/kernel/device-drivers— IRQ, DMA, regmap depthskills/kernel-dev/writing-char-drivers— userspace interfaceskills/kernel-dev/bus-drivers-i2c-spi— other bus typesskills/low-level-programming/linux-kernel-modules— module loading
