Commit 13977091 authored by Magnus Damm's avatar Magnus Damm Committed by Greg Kroah-Hartman

Driver Core: early platform driver

V3 of the early platform driver implementation.

Platform drivers are great for embedded platforms because we can separate
driver configuration from the actual driver.  So base addresses,
interrupts and other configuration can be kept with the processor or board
code, and the platform driver can be reused by many different platforms.

For early devices we have nothing today.  For instance, to configure early
timers and early serial ports we cannot use platform devices.  This
because the setup order during boot.  Timers are needed before the
platform driver core code is available.  The same goes for early printk
support.  Early in this case means before initcalls.

These early drivers today have their configuration either hard coded or
they receive it using some special configuration method.  This is working
quite well, but if we want to support both regular kernel modules and
early devices then we need to have two ways of configuring the same
driver.  A single way would be better.

The early platform driver patch is basically a set of functions that allow
drivers to register themselves and architecture code to locate them and
probe.  Registration happens through early_param().  The time for the
probe is decided by the architecture code.

See Documentation/driver-model/platform.txt for more details.

[ coding-style fixes]
Signed-off-by: default avatarMagnus Damm <>
Cc: Paul Mundt <>
Cc: Kay Sievers <>
Cc: David Brownell <>
Cc: Tejun Heo <>
Signed-off-by: default avatarAndrew Morton <>
Signed-off-by: default avatarGreg Kroah-Hartman <>
parent 31b07093
......@@ -169,3 +169,62 @@ three different ways to find such a match:
be probed later if another device registers. (Which is OK, since
this interface is only for use with non-hotpluggable devices.)
Early Platform Devices and Drivers
The early platform interfaces provide platform data to platform device
drivers early on during the system boot. The code is built on top of the
early_param() command line parsing and can be executed very early on.
Example: "earlyprintk" class early serial console in 6 steps
1. Registering early platform device data
The architecture code registers platform device data using the function
early_platform_add_devices(). In the case of early serial console this
should be hardware configuration for the serial port. Devices registered
at this point will later on be matched against early platform drivers.
2. Parsing kernel command line
The architecture code calls parse_early_param() to parse the kernel
command line. This will execute all matching early_param() callbacks.
User specified early platform devices will be registered at this point.
For the early serial console case the user can specify port on the
kernel command line as "earlyprintk=serial.0" where "earlyprintk" is
the class string, "serial" is the name of the platfrom driver and
0 is the platform device id. If the id is -1 then the dot and the
id can be omitted.
3. Installing early platform drivers belonging to a certain class
The architecture code may optionally force registration of all early
platform drivers belonging to a certain class using the function
early_platform_driver_register_all(). User specified devices from
step 2 have priority over these. This step is omitted by the serial
driver example since the early serial driver code should be disabled
unless the user has specified port on the kernel command line.
4. Early platform driver registration
Compiled-in platform drivers making use of early_platform_init() are
automatically registered during step 2 or 3. The serial driver example
should use early_platform_init("earlyprintk", &platform_driver).
5. Probing of early platform drivers belonging to a certain class
The architecture code calls early_platform_driver_probe() to match
registered early platform devices associated with a certain class with
registered early platform drivers. Matched devices will get probed().
This step can be executed at any point during the early boot. As soon
as possible may be good for the serial port case.
6. Inside the early platform driver probe()
The driver code needs to take special care during early boot, especially
when it comes to memory allocation and interrupt registration. The code
in the probe() function can use is_early_platform_device() to check if
it is called at early platform device or at the regular platform device
time. The early serial driver performs register_console() at this point.
For further information, see <linux/platform_device.h>.
......@@ -990,6 +990,8 @@ int __init platform_bus_init(void)
int error;
error = device_register(&platform_bus);
if (error)
return error;
......@@ -1020,3 +1022,240 @@ u64 dma_get_required_mask(struct device *dev)
static __initdata LIST_HEAD(early_platform_driver_list);
static __initdata LIST_HEAD(early_platform_device_list);
* early_platform_driver_register
* @edrv: early_platform driver structure
* @buf: string passed from early_param()
int __init early_platform_driver_register(struct early_platform_driver *epdrv,
char *buf)
unsigned long index;
int n;
/* Simply add the driver to the end of the global list.
* Drivers will by default be put on the list in compiled-in order.
if (!epdrv-> {
list_add_tail(&epdrv->list, &early_platform_driver_list);
/* If the user has specified device then make sure the driver
* gets prioritized. The driver of the last device specified on
* command line will be put first on the list.
n = strlen(epdrv->pdrv->;
if (buf && !strncmp(buf, epdrv->pdrv->, n)) {
list_move(&epdrv->list, &early_platform_driver_list);
if (!strcmp(buf, epdrv->pdrv->
epdrv->requested_id = -1;
else if (buf[n] == '.' && strict_strtoul(&buf[n + 1], 10,
&index) == 0)
epdrv->requested_id = index;
epdrv->requested_id = EARLY_PLATFORM_ID_ERROR;
return 0;
* early_platform_add_devices - add a numbers of early platform devices
* @devs: array of early platform devices to add
* @num: number of early platform devices in array
void __init early_platform_add_devices(struct platform_device **devs, int num)
struct device *dev;
int i;
/* simply add the devices to list */
for (i = 0; i < num; i++) {
dev = &devs[i]->dev;
if (!dev-> {
* early_platform_driver_register_all
* @class_str: string to identify early platform driver class
void __init early_platform_driver_register_all(char *class_str)
/* The "class_str" parameter may or may not be present on the kernel
* command line. If it is present then there may be more than one
* matching parameter.
* Since we register our early platform drivers using early_param()
* we need to make sure that they also get registered in the case
* when the parameter is missing from the kernel command line.
* We use parse_early_options() to make sure the early_param() gets
* called at least once. The early_param() may be called more than
* once since the name of the preferred device may be specified on
* the kernel command line. early_platform_driver_register() handles
* this case for us.
* early_platform_match
* @edrv: early platform driver structure
* @id: id to match against
static __init struct platform_device *
early_platform_match(struct early_platform_driver *epdrv, int id)
struct platform_device *pd;
list_for_each_entry(pd, &early_platform_device_list, dev.devres_head)
if (platform_match(&pd->dev, &epdrv->pdrv->driver))
if (pd->id == id)
return pd;
return NULL;
* early_platform_left
* @edrv: early platform driver structure
* @id: return true if id or above exists
static __init int early_platform_left(struct early_platform_driver *epdrv,
int id)
struct platform_device *pd;
list_for_each_entry(pd, &early_platform_device_list, dev.devres_head)
if (platform_match(&pd->dev, &epdrv->pdrv->driver))
if (pd->id >= id)
return 1;
return 0;
* early_platform_driver_probe_id
* @class_str: string to identify early platform driver class
* @id: id to match against
* @nr_probe: number of platform devices to successfully probe before exiting
static int __init early_platform_driver_probe_id(char *class_str,
int id,
int nr_probe)
struct early_platform_driver *epdrv;
struct platform_device *match;
int match_id;
int n = 0;
int left = 0;
list_for_each_entry(epdrv, &early_platform_driver_list, list) {
/* only use drivers matching our class_str */
if (strcmp(class_str, epdrv->class_str))
if (id == -2) {
match_id = epdrv->requested_id;
left = 1;
} else {
match_id = id;
left += early_platform_left(epdrv, id);
/* skip requested id */
switch (epdrv->requested_id) {
if (epdrv->requested_id == id)
switch (match_id) {
pr_warning("%s: unable to parse %s parameter\n",
class_str, epdrv->pdrv->;
/* fall-through */
match = NULL;
match = early_platform_match(epdrv, match_id);
if (match) {
if (epdrv->pdrv->probe(match))
pr_warning("%s: unable to probe %s early.\n",
class_str, match->name);
if (n >= nr_probe)
if (left)
return n;
return -ENODEV;
* early_platform_driver_probe
* @class_str: string to identify early platform driver class
* @nr_probe: number of platform devices to successfully probe before exiting
* @user_only: only probe user specified early platform devices
int __init early_platform_driver_probe(char *class_str,
int nr_probe,
int user_only)
int k, n, i;
n = 0;
for (i = -2; n < nr_probe; i++) {
k = early_platform_driver_probe_id(class_str, i, nr_probe - n);
if (k < 0)
n += k;
if (user_only)
return n;
* early_platform_cleanup - clean up early platform code
void __init early_platform_cleanup(void)
struct platform_device *pd, *pd2;
/* clean up the devres list used to chain devices */
list_for_each_entry_safe(pd, pd2, &early_platform_device_list,
dev.devres_head) {
memset(&pd->dev.devres_head, 0, sizeof(pd->dev.devres_head));
......@@ -247,6 +247,7 @@ struct obs_kernel_param {
/* Relies on boot_command_line being set */
void __init parse_early_param(void);
void __init parse_early_options(char *cmdline);
#endif /* __ASSEMBLY__ */
......@@ -77,4 +77,46 @@ extern int platform_driver_probe(struct platform_driver *driver,
#define platform_get_drvdata(_dev) dev_get_drvdata(&(_dev)->dev)
#define platform_set_drvdata(_dev,data) dev_set_drvdata(&(_dev)->dev, (data))
/* early platform driver interface */
struct early_platform_driver {
const char *class_str;
struct platform_driver *pdrv;
struct list_head list;
int requested_id;
extern int early_platform_driver_register(struct early_platform_driver *epdrv,
char *buf);
extern void early_platform_add_devices(struct platform_device **devs, int num);
static inline int is_early_platform_device(struct platform_device *pdev)
return !pdev->dev.driver;
extern void early_platform_driver_register_all(char *class_str);
extern int early_platform_driver_probe(char *class_str,
int nr_probe, int user_only);
extern void early_platform_cleanup(void);
#ifndef MODULE
#define early_platform_init(class_string, platform_driver) \
static __initdata struct early_platform_driver early_driver = { \
.class_str = class_string, \
.pdrv = platform_driver, \
.requested_id = EARLY_PLATFORM_ID_UNSET, \
}; \
static int __init early_platform_driver_setup_func(char *buf) \
{ \
return early_platform_driver_register(&early_driver, buf); \
} \
early_param(class_string, early_platform_driver_setup_func)
#else /* MODULE */
#define early_platform_init(class_string, platform_driver)
#endif /* MODULE */
#endif /* _PLATFORM_DEVICE_H_ */
......@@ -492,6 +492,11 @@ static int __init do_early_param(char *param, char *val)
return 0;
void __init parse_early_options(char *cmdline)
parse_args("early options", cmdline, NULL, 0, do_early_param);
/* Arch code calls this early on, or if not, just before other parsing. */
void __init parse_early_param(void)
......@@ -503,7 +508,7 @@ void __init parse_early_param(void)
/* All fall through to do_early_param. */
strlcpy(tmp_cmdline, boot_command_line, COMMAND_LINE_SIZE);
parse_args("early options", tmp_cmdline, NULL, 0, do_early_param);
done = 1;
Markdown is supported
0% or
You are about to add 0 people to the discussion. Proceed with caution.
Finish editing this message first!
Please register or to comment