Yes, both HSA contributions through your employer and directly to your HSA reduce your AGI and your MAGI.

Your MAGI (which determines your deductible IRA contribution limit) is determined by:

An individual's adjusted gross income  without taking into account any of the following amounts.

• IRA deduction.
• Student loan interest deduction.
• Tuition and fees deduction.
• Domestic production activities deduction.
• Foreign earned income exclusion.
• Foreign housing exclusion or deduction.
• Exclusion of qualified savings bond interest shown on Form 8815.
• Exclusion of employer-provided adoption benefits shown on Form 8839.

Note that neither type of HSA contribution appears here, so once the HSA information has been entered into TurboTax, you can apply the items above (if any) to add back to your AGI to determine your MAGI.