Asahi Creator: 1 monitor support is because of hardware limitation

[karen999]

Apple Silicon is a generational leap in terms of power and efficiency and yet people still saying "it's a low end chip". M1 MBA has been making all kinds of headlines of beating Mac Pros just several years ago. Are you not expecting technology to pushing forward? and making excuse for Apple going backwards on one of the crucial capabilities of a computer?

 

[leman]

That's amazing.

GPUs have been doing this for very long time. Nvidia is probably the most advanced in this regard. Apple is a relative newcomer but they have a bunch of interesting patents etc.

I think GPU. There's a probably a transformation matrix to describe scaling and also rotation. A texture from the source framebuffer is transformed by the matrix to an output framebuffer. Or maybe there's a more efficient way to do this. The output framebuffer also needs to be setup to include black bars or pillars when the aspect ratio of the source doesn't match the aspect ratio of the output.

Textures are not transformed with matrices. Nor does it make any sense to use such a heavy-weight tool in this context. Pixel data (scanout) is sent to the display sequentially, row by row. It would actually makes sense to use specialized display output hardware that performs texture resampling during the scan-out. I’m sure it can be made much more efficient than using GPU compute for this purpose.

 

[joevt]

Textures are not transformed with matrices. Nor does it make any sense to use such a heavy-weight tool in this context. Pixel data (scanout) is sent to the display sequentially, row by row. It would actually makes sense to use specialized display output hardware that performs texture resampling during the scan-out. I’m sure it can be made much more efficient than using GPU compute for this purpose.

Ok. Sounds like Tcon with scaling capability? Tcon = display timing controller.
Apple Intel GPU drivers mention Tcon for scaling. There's multiple instances with different code names Camellia and Banksia. I don't know what kind of scaling they do or if they do all kinds of scaling.

 

[senttoschool]

That doesn't make any sense because MacBook Air 2018-2020 supports 2 external displays.

MacBook Air 2017 and older supported one external display even though the Intel CPU supports two. Clearly, Apple thought it was important to add the supporting hardware for dual display in 2018.

Nothing will ever get past the fact that Apple supported one external display, then two, then back to one.

It makes perfect sense. M2 is also used on iPads which has just as much volume or maybe even more volume than low end Macs. Think of the M2 as more of an iPad SoC than Mac and it makes perfect sense.

 

[Romain_H]

It makes perfect sense. M2 is also used on iPads

Is that actually a thing?

 

[theluggage]

MacBook Air 2017 and older supported one external display even though the Intel CPU supports two. Clearly, Apple thought it was important to add the supporting hardware for dual display in 2018.

One physical display per port (even if it's a dual stream 5k) is a limitation of Thunderbolt 2 - the ability to support 2 up-to-4k displays on a single port is a Thunderbolt 3 feature.

MBA 2017 had a single Thunderbolt 2 port. Apple would have had to re-design the MacBook Air chassis to accommodate a second TB2, DisplayPort or HDMI port to support the extra display.

MBA 2018 used Thunderbolt 3 ports which solved the problem. Apple would have had to go out of their way to disable the extra display.

Having the display controllers on the processor able to support 3 displays, and choosing the tradeoffs with power/heat/transitor count/ vs. features was an Intel decision, and Intel were designing chips to satisfy a wide range of PC makers making widely different machines (if you dig around on ark.intel.com you'll see that it was up to PC makers whether to configure all of the display outputs). It's only with Apple Silicon that Apple had the opportunity to decide on their own "trade offs".

 

[joevt]

One physical display per port (even if it's a dual stream 5k) is a limitation of Thunderbolt 2 - the ability to support 2 up-to-4k displays on a single port is a Thunderbolt 3 feature.

Thunderbolt 1/2 always allowed two displays per port. Remember that you can chain two Apple Thunderbolt Displays (which are Thunderbolt 1) together to a Thunderbolt 1 or Thunderbolt 2 Mac.

Thunderbolt 1 and Thunderbolt 2 have the same bandwidth - 20Gbps - except Thunderbolt 2 combines the two 10 Gbps channels into a single 20 Gbps link.

A 2560x1600 display is only 8 Gbps, so a Thunderbolt 1 or Thunderbolt 2 cable can carry two of those (HBR link rate = 8.64 Gbps).

Thunderbolt 1 and Thunderbolt 2 docks have a limit of supporting 1 display, but you can chain docks together to support 2 displays. Or you can connect a Thunderbolt 3 dock to a Thunderbolt 1/2 Mac to connect two displays to the same Thunderbolt 3 dock. A Thunderbolt 3 to Dual DisplayPort Adapter can also work. The only one with a female connector that can be used with the Apple Thunderbolt 3 to Thunderbolt 2 Adapter is the OWC Thunderbolt 3 to Dual DisplayPort Adapter but I don't know if there's enough power from the Apple Adapter to make that work. In any case, you can connect the adapter to a Thunderbolt 3 dock which has its own power.

The 10 Gbps channels of Thunderbolt 1 don't have enough bandwidth for 4K60 (16 Gbps). Thunderbolt 2 can connect one 4K60 display. Thunderbolt 3/4 can connect two 4K60 displays.

MBA 2017 had a single Thunderbolt 2 port. Apple would have had to re-design the MacBook Air chassis to accommodate a second TB2, DisplayPort or HDMI port to support the extra display.

Thunderbolt 2 can support two displays like I said above, but maybe the Intel HD Graphics 6000 can't support three displays (including the built-in)?

MBA 2018 used Thunderbolt 3 ports which solved the problem. Apple would have had to go out of their way to disable the extra display.

Intel UHD Graphics 617 can support three displays (including the built-in).

 

[Amethyst1]

One physical display per port (even if it's a dual stream 5k) is a limitation of Thunderbolt 2 [...]

Thunderbolt 1 and Thunderbolt 2 can run two displays per port. I've done it.

MBA 2017 had a single Thunderbolt 2 port. [...]

2012 and later MBAs can all run two external displays using their single Thunderbolt 1/2 port. You just need two Thunderbolt displays, two TB1/TB2 docks or a single TB3 dock as @joevt explained.

The 2011 MBA is the exception: it can only run one external display because it's using a cut-down (Intel DSL2310) Thunderbolt controller (cf.: "DP 1.1a 1x Sink").

[...] maybe the Intel HD Graphics 6000 can't support three displays (including the built-in)?

The Intel HD Graphics 4000 (2012) and newer Intel iGPUs can run three displays. "Xe" can run four. I don't have a system with the HD Graphics 6000 but I have one with the Iris Pro 6200 (same generation) and it runs three displays just fine.

 

[theluggage]

2012 and later MBAs can all run two external displays using their single Thunderbolt 1/2 port. You just need two Thunderbolt displays, two TB1/TB2 docks or a single TB3 dock as @joevt explained.

I stand corrected - YMMV as to whether chaining multiple TB1/2 docks or expensive TB displays (you can't chain a DisplayPort display to the TB1 Thunderbolt display) to a MBA with Intel HD6000 integrated graphics is something that Apple would advertise as "supported". I don't think TB3 docks with multiple display support were even available when those machines launched.

However, if you're right about 2012> MBAs supporting 2 external displays, then the post by @JPack I was responding to claiming that Apple added the hardware for 2 ext displays in 2018 was wrong too, so it's all a bit moot.

 

[Amethyst1]

I stand corrected - YMMV as to whether chaining multiple TB1/2 docks or expensive TB displays (you can't chain a DisplayPort display to the TB1 Thunderbolt display) to a MBA with Intel HD6000 integrated graphics is something that Apple would advertise as "supported".

Daisy-chaining two 27” Thunderbolt Displays has been an officially supported setup since day one, even on a 2011 13” MBP’s truly sh**ty Intel HD 3000, which a HD 6000 runs circles around — unless you had the 2011 MBA with its “crippled” Thunderbolt controller.

 

[theluggage]

Daisy-chaining two 27” Thunderbolt Displays has been an officially supported setup since day one, even on a 2011 13” MBP’s truly sh**ty Intel HD 3000, which a HD 6000 runs circles around — unless you had the 2011 MBA with its “crippled” Thunderbolt controller.

I'm still standing corrected on the only-1-display-per-port thing (although pedantically true), but otherwise works is not the same thing as supported. For most of the pre-2018 MacBook Air models, Apple only lists one external display in their specs.

EG:

MacBook Air (13-inch, 2017) - Technical Specifications – Apple Support (UK)

support.apple.com

 

[Amethyst1]

I'm still standing corrected on the only-1-display-per-port thing (although pedantically true), but otherwise works is not the same thing as supported.

I totally agree, but was the original question whether it is supported or whether it works?

 

[JPack]

If the question was simply whether it works, then end of discussion. M1/M2 works if you buy a DisplayLink dock. Clearly, this thread is focused on Apple's efforts on supporting dual external displays.

• MacBook Air pre-2018 supports 1 external display
• MacBook Air 2018-2020 supports 2 external displays
• MacBook Air M1/M2 supports 1 external display

It's clear Apple found dual-display support important. There are many entry level notebooks that do not support dual-external displays even if the Intel/AMD silicon does. So the idea that MacBook Air is some low end device not deserving Apple sanctioned dual external display support is ridiculous.

 

[jdb8167]

Sure, but I think the question is, "Did Apple make the right trade off?"

With M2 vs. M1, there are 25% more transistors and floor area is 30% larger. Are there more people editing in ProRes rather driving two FHD monitors? Regular iPhone 13 can't even record ProRes.

Which is why I mentioned ProRes. I don't value ProRes at all but obviously Apple thinks that many will. Is that a correct decision? Not for me but I suppose Apple knows its market. I have no use for dual monitor support on a MacBook Air either but given the choice between ProRes or dual displays, I would take dual displays every time.

Apple makes decisions like this on every product they make. They are going to choose where to expend their transistors. If you find the decision lacking, the obvious thing to do is not buy the product. If enough people do the same, Apple will make a different decision next time. Unfortunately for the many tech-addicts in these forums that desperately want dual displays, the majority of MacBook Air users almost certainly don't use dual displays. I suspect that many MBA users don't even use one external display.

Luckily Apple does make notebooks that support more than one external display. It is a bigger and heavier notebook but those are just more tradeoffs.

 

[JPack]

It makes perfect sense. M2 is also used on iPads which has just as much volume or maybe even more volume than low end Macs. Think of the M2 as more of an iPad SoC than Mac and it makes perfect sense.

That logic probably only makes sense to you. 😄

Look at the product revenue breakdown Apple provides each quarter. Count the number of Mac products powered by M1/M2.

When Johny Srouji says the M1 and M2 are designed specifically for Mac, he's lying, right? When Apple launches M-series chips on Macs a full 6 months before it gets trickled down to high-end iPads is merely a coincidence, right?

I wouldn't be surprised if you thought A12 is an Apple TV SoC and the S5 is actually designed for the HomePod mini.

 

[jdb8167]

Is that actually a thing?

Not yet. The expectation is that the M2 is going to go into the next iPad Pro/Air but it is just an educated guess. It's entirely possible that Apple skips the bigger and hotter M2 and waits for the M3 for the next iPad Pro. I do expect a down clocked M2 iPad Pro though.

 

[JPack]

Which is why I mentioned ProRes. I don't value ProRes at all but obviously Apple thinks that many will. Is that a correct decision? Not for me but I suppose Apple knows its market. I have no use for dual monitor support on a MacBook Air either but given the choice between ProRes or dual displays, I would take dual displays every time.

Apple makes decisions like this on every product they make. They are going to choose where to expend their transistors. If you find the decision lacking, the obvious thing to do is not buy the product. If enough people do the same, Apple will make a different decision next time. Unfortunately for the many tech-addicts in these forums that desperately want dual displays, the majority of MacBook Air users almost certainly don't use dual displays. I suspect that many MBA users don't even use one external display.

Luckily Apple does make notebooks that support more than one external display. It is a bigger and heavier notebook but those are just more tradeoffs.

The available evidence suggests Apple believes many MacBook Air owners do use dual external displays. That's why Apple added the feature in 2018 to MacBook Air when it was lacking before.

This is not a technical limitation about transistor budget or power consumption, but rather a marketing decision to segment the product from the start.

 

[jdb8167]

The available evidence suggests Apple believes many MacBook Air owners do use dual external displays. That's why Apple added the feature in 2018 to MacBook Air when it was lacking before.

This is not a technical limitation about transistor budget or power consumption, but rather a marketing decision to segment the product from the start.

Apple didn't add it, Intel did. It was a feature of the Intel CPU that they used. Or are you claiming that a second display controller doesn't use any transistors? In which case, you are wrong.

 

[JPack]

Apple didn't add it, Intel did. It was a feature of the Intel CPU that they used. Or are you claiming that a second display controller doesn't use any transistors? In which case, you are wrong.

Apple added hardware/software to support a second external display. Already explained above.

 

[jdb8167]

Apple added hardware/software to support a second external display. Already explained above.

Huh? What hardware/software? Daisy chaining Thunderbolt displays is part of the Intel CPU and chipset. As said above, all MacBook Airs since 2012 could run multiple displays.

2012 and later MBAs can all run two external displays using their single Thunderbolt 1/2 port. You just need two Thunderbolt displays, two TB1/TB2 docks or a single TB3 dock as @joevt explained.

And you didn't answer my question. Do you somehow believe that a second display controller doesn't use any transistors? Because if you admit that it does use transistors, then Apple used those potential display controller transistors for something else.

 

[hans1972]

Snapdragon 8c supports dual 4K external monitors. Does Qualcomm not care about power consumption?

It also has half the transistors compared to M2.

These guys are just working backwards to come up with an excuse for Apple.

Apple needed to support 5K/6K for at least one monitor or else you Apple would be selling monitors which couldn't be used to the full extent with the MacBook Air.

Qualcomm did the correct trade-off for them. No Windows for Arm users are going to connect anything more than 4K monitors since Windows (for Arm) users don't really care about high-resolution screens.

Apple chose a trade-off which didn't suit them and so you don't have any choice to 1) stop using one monitor, 2) buying a more expensive Mac or 3) use a Windows for Arm PC with Qualcomm's Snapdragon 8C SoC.

 

[joevt]

you can't chain a DisplayPort display to the TB1 Thunderbolt display

True. The TB1 Thunderbolt Display is like a Thunderbolt 1 dock with a display connected to the dock. Thunderbolt 1 docks only support one display. Therefore, to connect a DisplayPort display to the TB1 Thunderbolt Display, you need another Thunderbolt dock.

I don't think TB3 docks with multiple display support were even available when those machines launched.

Yet TB3 docks are perfectly compatible with TB1/TB2 Macs using the Apple Thunderbolt 3 to Thunderbolt 2 Adapter (the adapter works in both directions). A Thunderbolt 3 dock can connect two displays.

TB4 docks don't work well with TB1/TB2 Macs probably because Apple won't update the TB1/TB2 drivers. Actually, the EFI of TB1/TB2 Macs supports TB4 docks better than macOS such that you might be able to connect it before boot for it to work, but you can't hot plug it after macOS boots.

 

[theluggage]

Yet TB3 docks are perfectly compatible with TB1/TB2 Macs using the Apple Thunderbolt 3 to Thunderbolt 2 Adapter (the adapter works in both directions). A Thunderbolt 3 dock can connect two displays.

Sure, but the discussion was about why Apple chose not to officially support (even if it worked unofficially) two external displays on pre-2018 MBAs. TB3 docks were new & rare in 2017 and didn't exist in 2015 - and I think it's understandable why Apple didn't say "Supports 2 external displays (small print: only by daisy-chaining a second expensive Thunderbolt 1/2 device to your entry-level laptop)".

Bottom line: The 2018 MBA had two TB3 ports so - since the Intel CPU supported it - connecting 2 displays "just works". Prior to that it would have come with a list of ifs, buts and expensive pre-requisites.

 

[livmatus]

to all who think people don't use dual external monitors with a $999 machine ... we use $600 Dell laptops in a company where there are 800+ desks with ... you guessed what ... a dual monitor setup!

still I think when Asahi creators get the Display Port to work, it will drive two separate external monitors using DP MST

 

[MrGunny94]

to all who think people don't use dual external monitors with a $999 machine ... we use $600 Dell laptops in a company where there are 800+ desks with ... you guessed what ... a dual monitor setup!

still I think when Asahi creators get the Display Port to work, it will drive two separate external monitors using DP MST

Same.. The main reason I go the M1 Pro was because it supported dual displays at high refresh rate / high resolution.

Good luck getting anything productive done on a single monitor when you are working with multiple stacks, spreadsheets and browser tabs.