I recently purchased a Precision 7540, and have had success tweaking the power settings of the processor using Brendan Greenley's guide:
Undervolting 2020 Dell Laptops
For anyone interested I've attached the BIOS dump from v1.24. I'm currently on BIOS v1.26.1, and can confirm that the same settings work.
In the GRUB terminal, the relevant commands are (the forum software changes all "x'es" to multiplication signs - not sure how to fix this?):
Overclocking Lock: setup_var Setup 0x789 0x1
CFG Lock: setup_var Setup 0x6ed 0x1
Overclocking Feature: setup_var Setup 0x856 0x1
With these changes, I was able to achieve a stable undervolt of -120 mV cache and -150 mV core on my i9-9980HK using Throttlestop. On stock cooling, the Cinebench R20 multicore score increased from 3550 to 4060.
However, Dell has appeared to limit the power limits to 75W for PL1, and 107W for PL2. Changes in Throttlestop beyond these limits do not take.
That's when I found this article about the ability of IMON Slope to effectively increase power limits by reporting only a percentage of the power draw to the controller: [GUIDE] Unlock the EC TDP limit of your low power U series Intel CPU
The Precision 7540 BIOS does have four IMON Slope variables, which are normally set to 0x0 (disabled / power reported = actual power). On the stock cooling, the processor already reaches thermal limits at 107W, but I wanted to increase the PL1 to improve sustained performance. I was able to successfully change the IMON Slope to 90, making the effective PL1 (75W / 0.9) = 83W. I also reduced the PL2 to 96W to maintain the same effective power limit. Here are the changes I made:
setup_var Setup 0x8ac 0x5A
setup_var Setup 0x8ae 0x5A
setup_var Setup 0x8b2 0x5A
setup_var Setup 0x8b4 0x5A
As a result, the processor sustained ~3850 mhz on all cores at 90-92 °C at PL1, resulting in a Cinebench R20 multicore score of 4279!
I have plans to upgrade the cooling solution by re-pasting with PTM7950, replacing thermal pads, and doing the Delta fan mod mentioned elsewhere in this thread. I have all the parts, but lack time - so I will report the improvements in a couple of months, after complete.
File_DXE_driver_Setup IFR.txt