request_firmware API¶

You would typically load firmware and then load it into your device somehow. The typical firmware work flow is reflected below:

if(request_firmware(&fw_entry, $FIRMWARE, device) == 0)
       copy_fw_to_device(fw_entry->data, fw_entry->size);
release_firmware(fw_entry);

Synchronous firmware requests¶

Synchronous firmware requests will wait until the firmware is found or until an error is returned.

request_firmware¶

int request_firmware(const struct firmware ** firmware_p, const char * name, struct device * device)¶: send firmware request and wait for it

Parameters

const struct firmware ** firmware_p: pointer to firmware image
const char * name: name of firmware file
struct device * device: device for which firmware is being loaded

Description

firmware_p will be used to return a firmware image by the name of name for device device.

Should be called from user context where sleeping is allowed.

name will be used as $FIRMWARE in the uevent environment and should be distinctive enough not to be confused with any other firmware image for this or any other device.

Caller must hold the reference count of device.

The function can be called safely inside device’s suspend and resume callback.

firmware_request_nowarn¶

int firmware_request_nowarn(const struct firmware ** firmware, const char * name, struct device * device)¶: request for an optional fw module

Parameters

const struct firmware ** firmware: pointer to firmware image
const char * name: name of firmware file
struct device * device: device for which firmware is being loaded

Description

This function is similar in behaviour to request_firmware(), except it doesn’t produce warning messages when the file is not found. The sysfs fallback mechanism is enabled if direct filesystem lookup fails, however, however failures to find the firmware file with it are still suppressed. It is therefore up to the driver to check for the return value of this call and to decide when to inform the users of errors.

request_firmware_direct¶

int request_firmware_direct(const struct firmware ** firmware_p, const char * name, struct device * device)¶: load firmware directly without usermode helper

Parameters

const struct firmware ** firmware_p: pointer to firmware image
const char * name: name of firmware file
struct device * device: device for which firmware is being loaded

Description

This function works pretty much like request_firmware(), but this doesn’t fall back to usermode helper even if the firmware couldn’t be loaded directly from fs. Hence it’s useful for loading optional firmwares, which aren’t always present, without extra long timeouts of udev.

request_firmware_into_buf¶

int request_firmware_into_buf(const struct firmware ** firmware_p, const char * name, struct device * device, void * buf, size_t size)¶: load firmware into a previously allocated buffer

Parameters

const struct firmware ** firmware_p: pointer to firmware image
const char * name: name of firmware file
struct device * device: device for which firmware is being loaded and DMA region allocated
void * buf: address of buffer to load firmware into
size_t size: size of buffer

Description

This function works pretty much like request_firmware(), but it doesn’t allocate a buffer to hold the firmware data. Instead, the firmware is loaded directly into the buffer pointed to by buf and the firmware_p data member is pointed at buf.

This function doesn’t cache firmware either.

Asynchronous firmware requests¶

Asynchronous firmware requests allow driver code to not have to wait until the firmware or an error is returned. Function callbacks are provided so that when the firmware or an error is found the driver is informed through the callback. request_firmware_nowait() cannot be called in atomic contexts.

request_firmware_nowait¶

int request_firmware_nowait(struct module * module, bool uevent, const char * name, struct device * device, gfp_t gfp, void * context, void (*cont) (const struct firmware *fw, void *context)¶: asynchronous version of request_firmware

Parameters

struct module * module: module requesting the firmware
bool uevent: sends uevent to copy the firmware image if this flag is non-zero else the firmware copy must be done manually.
const char * name: name of firmware file
struct device * device: device for which firmware is being loaded
gfp_t gfp: allocation flags
void * context: will be passed over to cont, and fw may be NULL if firmware request fails.
void (*)(const struct firmware *fw, void *context) cont: function will be called asynchronously when the firmware request is over.

Description

Caller must hold the reference count of device.

Asynchronous variant of request_firmware() for user contexts:

sleep for as small periods as possible since it may increase kernel boot time of built-in device drivers requesting firmware in their ->probe() methods, if gfp is GFP_KERNEL.

can’t sleep at all if gfp is GFP_ATOMIC.

Special optimizations on reboot¶

Some devices have an optimization in place to enable the firmware to be retained during system reboot. When such optimizations are used the driver author must ensure the firmware is still available on resume from suspend, this can be done with firmware_request_cache() instead of requesting for the firmware to be loaded.

firmware_request_cache()¶

int firmware_request_cache(struct device * device, const char * name)¶: cache firmware for suspend so resume can use it

Parameters

struct device * device: device for which firmware should be cached for
const char * name: name of firmware file

Description

There are some devices with an optimization that enables the device to not require loading firmware on system reboot. This optimization may still require the firmware present on resume from suspend. This routine can be used to ensure the firmware is present on resume from suspend in these situations. This helper is not compatible with drivers which use request_firmware_into_buf() or request_firmware_nowait() with no uevent set.

request firmware API expected driver use¶

Once an API call returns you process the firmware and then release the firmware. For example if you used request_firmware() and it returns, the driver has the firmware image accessible in fw_entry->{data,size}. If something went wrong request_firmware() returns non-zero and fw_entry is set to NULL. Once your driver is done with processing the firmware it can call call release_firmware(fw_entry) to release the firmware image and any related resource.