Pass a Multi-Value Parameter to Stored Procedure

[mynameant]

Hi all, I am using CRXI and have a report based on an Oracle based Stored procedure. I need to make the parameter on this report as multi- value parameter which I cannot directly. So, I am doing something like this using a sub-report.

Main Report:
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Empty report with a parameter TYPES. Made this parameter as multi value paramter and added few values. So user has option to select more than one value.
Sub Report:
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Now, I have created a sub report based on the stored procedure with one parameter p_types [Character data type].

If I Link main report and Sub report directly on this parameter value, I am not getting any values passed to sub-report. so, I tried to create a formula to make all the values in this parmeter from main report as a comma seperated string nad trying to link sub-report based on this formula. But I am not able to get it work.
I am using something like this in my formula:
join({?TYPES},",")

and it shows all the values in the formula as expected. but when I link this to sub -report it doesn't work.
Any other ideas? Anyone faced this before?

Thanks for all the help you can provide.