The flow for production supply is that you are supposed to create the Transfer order from TR (if you are using standard SAP storage type then system will propose to pick the stock from warehouse and drop to storage type 100)
once you confirm the transfer order in 100 then using Posting change functionality you can transfer the stock from storage location L001 to P001 (use MIGO --Transfer Posting / 311) or you can use the "storage location control" functionality to perform the posting change once you confirm the transfer order in storage type 100
to set up the storage location control you can refer the existing SCN thread