PREFERRED_PROVIDER and PREFERRED_VERSION in Yocto

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When we run "bitbake <target>", bitbake looks at the PROVIDES variable of each recipe to find out the recipe for the particular target. The Default value of PROVIDES is PN.

PN --> Name of the Recipe
PV --> Version of the Recipe
PR --> Revision of the Recipe

PREFERRED_PROVIDER: Sometimes a target can have multiple providers. PREFERRED_PROVIDER determines which recipe should be given preference when multiple recipes provide the same item.

E.g. virtual/kernel, u-boot will be provided by multiple recipes
PREFERRED_PROVIDER_virtual/kernel = "linux-imx"
PREFERRED_PROVIDER_u-boot = "uboot-imx"

This should be written in local.conf or machine.conf

PREFERRED_VERSION: When multiple versions of  a recipe are available, this variable determines which recipe should be given preference. If we don't state the version, bitbake will pick up the highest version.

E.g. PREFERRED_VERSION_linux-imx = "3.10.17-1.0.0"
PREFERRED_VERSION_u-boot-imx = "2013-04"



In the above screenshot, "linux-yocto" is selected as the provider for kernel.
You can also see there are multiple linux-yocto recipes. With PREFERRED_VERSION, version is set to 4.18%. The % matches any number of characters, useful when version numbers is long. 

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