linux-sg2042/Documentation/driver-api/firmware/lookup-order.rst

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Firmware lookup order
=====================
Different functionality is available to enable firmware to be found.
Below is chronological order of how firmware will be looked for once
a driver issues a firmware API call.
* The ''Built-in firmware'' is checked first, if the firmware is present we
return it immediately
* The ''Firmware cache'' is looked at next. If the firmware is found we
return it immediately
* The ''Direct filesystem lookup'' is performed next, if found we
return it immediately
* If no firmware has been found and the fallback mechanism was enabled
the sysfs interface is created. After this either a kobject uevent
is issued or the custom firmware loading is relied upon for firmware
loading up to the timeout value.