ARM and GPU extensibility


veloknight

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I recently found out that there are ARM SoCs that have some PCIe lanes, which surprised me. If that's true, I'm surprised nobody's tried to use this, especially in the hardcore Free Software spaces: For x86 PCs, we have good free GPU drivers for old Nvidia cards, but can't use modern CPUs due to Intel ME and AMD PSP - while for the ARM space, even new CPUs which can have the TrustZone stuff disabled. My first instinct was, "wow, you could sell a system with free drivers and still have modern CPU this way" - I'm sure the real reason nobody's tried this is because it's hard to avoid other blobbed areas in ARM, particularly the higher-power/performance ARM chips. Still, the idea of being able to combine an ARM device with off-the-shelf PC parts got me thinking about eGPUs, perhaps for a Pyra successor or dock.

On that note, does anyone know if there are any known ARM vendors that offer Thunderbolt or similar type functionality in their SoCs?
 

hns

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I recently found out that there are ARM SoCs that have some PCIe lanes
Interesting. Do you have some examples?

Intel seems to have an external Thunderbolt controller so it could work with other SoC: DSL3510L
 

Exophase

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Interesting. Do you have some examples?

There's a decent number, not so much in the mobile SoC space but in stuff targeting automotive it's more common. A few off the top of my head:

- nVidia Tegra X1 has PCIe gen2 up to x4 + x1, not sure about X2 but I'd guess it has at least as much
- Freescale QorIQ line has PCIe gen3 up to x8
- TI DRA74x (which is vaguely similar to OMAP5) has PCIe gen2 x1, probably not enough for any decent GPU

This is just recent stuff. All three companies have supported PCIe in various ARM SoCs going back many years. Marvell has also had support. And there are FPGAs with integrated ARM hard cores where you could implement PCIe lanes.

With the Tegra X1 or X2 you get an nVidia desktop-class GPU anyway so you don't exactly need to try to attach a discrete external GPU just to be able to use open source drivers.
 
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