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With the latest PB, late yesterday came a new FW update.  It's now MP51.0084.B00.

Lou

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I can't remember which one it was, but Rominator ran into a Pascale nVidia GPU that essentially used virtually no power off of the PCIe bus whatsoever. It all really depends on how the card is designed. And the newer and more power hungry cards can cause problems if any other cards are in the machine because that 75w PCIe bus power is for all slots combined. It would actually make more sense to design a GPU to sip power from the PCIe bus (primarily for boot functionality) and draw the remaining power needed from the PCIe power connections directly from the PSU. PC mobo manufacturers get away with being able to SLI power hungry cards by using a PEG connector (SATA power connector directly on the mobo itself) to give the PCIe bus extra juice for stability. Mac Pros don't have that luxury, so if your GPU sucks down 75w of power, good luck powering that RAID card too if it doesn't have external power connections.

It's 75W per slot, 300W in total for all 4 slots.

Does anyone have a suggestion why the presence of the RX460 in a MacPro 5,1 with a stock Apple HD2600XT (as a helper card) prevents the machine booting with a spinner freeze about 1 cm from the right end of the boot progress bar (point where graphics driver loads)?  Without the RX460, the boot is normal.
Should the cards be in specific slots? I'd guess not but perhaps there is some voodoo....
My gut feeling is that Apple screwed the pooch with the AMDX4000driver bundle in some way.

I put up a webpage with nice big photos here http://www.hatsuon.net/cMP_5.0_MOD.html

Enjoy !

Thanks to the above hint from Rominator, SMIKX and myself were able to find the solder pads on the relatively ancient Sapphire Vapor-X HD5870 that control the PCIe Gen2 5 GT/s Link speed.
Looking at the back of this card with the Crossfire connector uppermost, you'll see a row of three vertical solder pads sitting in almost empty space below the left row of CF board edge connectors.  I soldered a chip resistor to bridge the two pads furthest from the CF connector and fired up the card (which is flashed with the Netkas rom—thanks Netkas). It shows the following (see screenshot).

SMIKX confirmed this with a 2B pencil using a graphite pencil line between the same two pads.  He has also confirmed the same pads on the HIS 5870.  (The photos of the two boards are from SMIKX.)

The solder job is relatively easy because there is plenty of space around the empty pads—just make sure to clean them first and use a very fine pair of chip tweezers to hold the chip resistor in place while tacking one side and then complete the solder.  Use a good electronics iron or soldering station too. Be sure there are no solder bridges.

It's a small improvement in speed for a little work.

Meanwhile, the search for a solution to why the RX460 does not boot in High Sierra continues.

[all]

I can't remember which one it was, but Rominator ran into a Pascale nVidia GPU that essentially used virtually no power off of the PCIe bus whatsoever. It all really depends on how the card is designed. And the newer and more power hungry cards can cause problems if any other cards are in the machine because that 75w PCIe bus power is for all slots combined. It would actually make more sense to design a GPU to sip power from the PCIe bus (primarily for boot functionality) and draw the remaining power needed from the PCIe power connections directly from the PSU. PC mobo manufacturers get away with being able to SLI power hungry cards by using a PEG connector (SATA power connector directly on the mobo itself) to give the PCIe bus extra juice for stability. Mac Pros don't have that luxury, so if your GPU sucks down 75w of power, good luck powering that RAID card too if it doesn't have external power connections.

Just run Luxmark then you will know if OpenCL is working or not.

I put up a ( HIS ) HD 7950 3Gb 5.0 GT/s mod tutorial

If there are only two revisions of the 7950 PCB's then this guide should probably be OK for all AMD reference 7950 3Gb cards.

HERE   https://forums.macrumors.com/threads/how-to-make-link-speed-2-5gt-s-to-5-0gt-s-on-ati-card-and-nvidia-card.1547340/page-8#post-24856990

Now I have to bone up on whether flashed 7950's need to have Open CL activated.

GPUz does not show OpenCL as being activated. Anyone have any information re this ?

kext edit ?

Some GPUs don't even make use of the PCIe bus power except for booting up. Granted AMDs aren't among them (they're power hungry), but don't count on that PCIe bus power limit being able to be counted toward the cap - it isn't always in use. The 225w level is the only truly "safe" power ceiling for the Mac Pros. Getting above that is a YMMV and will undoubtedly be case by case depending on the GPU in use. You can get 300w with the two mobo connectors + SATA to 8-pin connector, but for some reason the Mac Pros are super finnicky with regard to power under load. Just ask Rominator about those quirks. He's seen power draw that defied logic many times. Usually the problematic suspect is the motherboard PCIe power lines since mobo traces just weren't meant to transfer that kind of power. Apple chose unwisely back then. Entrepreneuring users can of course find ways around that.

Still, if it's a first gen Polaris GPU, I'd stay the hell away from those even though it looks like Apple's AMD drivers contain AMD's PCIe bus draw limit "fix" in them.

May I know which graphic card that has 6pins or even 8pins connectors but doesn't use PCIe slot power?

I know lots of card won't pull 75W from slot, may be just 25-35W even under stress, but really don't know a card that only pull power from slot during boot (but pulling zero under Furmark).

That 225W limit is definitely assuming we pull 75 from slot, 75 from 6pin A, and 75 from 6pin B.

Also, if we talking about 100% technically safe config, then we should not use SATA to 8pin, not even dual SATA to 8pin. A 8pin is rated up to 150W, a SATA port only rated up to ~55W, even dual SATA port's limit is nowhere near 150W.

In general, we don't really need to care the card's TDP, but only the config of the card. If it has a 6pin, then connect it to the mini 6pin. If it has a 8pin, connect it to 2x mini 6pin. If it has 6+8pin, then connect the 6pin to 2x SATA, and the 8pin to 2x mini 6pin.

If the card's TDP is 225, but only come with dual 6pin, then it is safe to run this card in a cMP with just the dual mini 6pin.

If the card's TDP is 375W, then connect it to 2x mini 6pin + 2x SATA is also safe. I can't see how a card that rated > 225W TDP is unsafe for cMP especially you mentioned about the SATA power.

Anyway, the mini 6pin on the cMP can practically deliver up to ~120W. 225W even zero power from slot is still OK for the cMP. And I really don't know any card that has 225W TDP, come with dual 6pin, but drawing zero power from slot, and natively draw way more than 75W from the 6pins.

But I totally agree that we should avoid the gen 1 RX480. I don't believe that MacOS's driver has the power draw fix. And I really don't want the card draw too much and kill the slot (or even the logic board).

Some GPUs don't even make use of the PCIe bus power except for booting up. Granted AMDs aren't among them (they're power hungry), but don't count on that PCIe bus power limit being able to be counted toward the cap - it isn't always in use. The 225w level is the only truly "safe" power ceiling for the Mac Pros. Getting above that is a YMMV and will undoubtedly be case by case depending on the GPU in use. You can get 300w with the two mobo connectors + SATA to 8-pin connector, but for some reason the Mac Pros are super finnicky with regard to power under load. Just ask Rominator about those quirks. He's seen power draw that defied logic many times. Usually the problematic suspect is the motherboard PCIe power lines since mobo traces just weren't meant to transfer that kind of power. Apple chose unwisely back then. Entrepreneuring users can of course find ways around that.

Still, if it's a first gen Polaris GPU, I'd stay the hell away from those even though it looks like Apple's AMD drivers contain AMD's PCIe bus draw limit "fix" in them.

The 6-pin connectors are 75watt each, the PCI bus another 75watt, so that's the 225watt you are talking about. A 5870 has a TDP of 188, 228 for the 2GB version. The 7950 has a TDP of 200watt. All supported in a standard Mac Pro.

Adding a SATA to 8-pin would raise your limit to 375watt, more then adequate for modern GPUs.

If you are concerned about pushing your PSU; my Mac Pro with a R9 290X (OC to 1100MHz), a W3690, 24GB, 2x PCIe M.2 SSDs, will draw just over 400watt max, measured at the wall, while playing games at 3440x1440@75Hz on max settings (Pixlas power mod). Idle it will sit around 90-140watt.

The PSU in a Mac Pro is rated at 980watt, the R9 290X has a TDP of 250watt (no OC, 1000MHz clock), the W3690 has a TDP of 130watt.
Yes, I removed all HDD and the DVD, never use the DVD anyway. For storage I use a NAS, or you could go eSATA.