The future of 32-bit Linux [LWN.net]

The future of 32-bit Linux

Posted Dec 8, 2020 10:42 UTC (Tue) by mzyngier (subscriber, #32898)
Parent article: The future of 32-bit Linux

Small correction:

> The latest generation of Armv8.2 cores have dropped hardware support for running 32-bit kernels completely. This includes the "little" Cortex-A55 [...]

A55 supports 32bit at all exception levels, and so does A75. Hopefully these are the last ARM 64bit cores to support 32bit at privileged exception levels.

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The future of 32-bit Linux

Posted Dec 8, 2020 15:34 UTC (Tue) by arnd (subscriber, #8866) [Link] (2 responses)

Thanks for the correction. I had actually looked it up but then forgot I already had the incorrect information in the article. I should have written "Most newer Armv8.2 cores starting with the Cortex-A76 ...".

I fear the Cortex-A53/A35/A55 cores are still going to be used in new SoCs for a while though. Maybe we can add a boot-time warning into the kernel to alert users that running 32-bit kernels is a bad idea and they should be using 64-bit kernels with 32-bit user space instead.

The future of 32-bit Linux

Posted Dec 8, 2020 17:17 UTC (Tue) by james (guest, #1325) [Link] (1 responses)

I suspect it's worse than that. There are a number of new phone SoCs with A73 and A53 (Snapdragon 662/665/460/439, Exynos 9610) that are going into fairly cheap phones (such as the £130 Nokia 5.3).

Which makes it look as though Arm are licensing the A73 core cheaply as an intermediate level between the in-order A55 and the high-end A76 and above, giving it a new lease of life.

The future of 32-bit Linux

Posted Dec 8, 2020 20:37 UTC (Tue) by arnd (subscriber, #8866) [Link]

I suspect it's more tied to the manufacturing process than with licensing: Cortex-A73/A53 based SoCs started out as high-end designs on 14nm, which can be refreshed into a 12nm or 11nm product without doing a complete redesign.

Cortex-A75/A55 usually started out on 10nm, with a possible shrink to 8nm. It appears that this generation is not economical yet for a small low-end to mid-range chip like the Snapdragon 66x, and the Snapdragon 460 looks like a co-design of that, if not the same chip in a lower bin.

I would not expect the Cortex-A73/A53 generation to be nearly as long-lived as the pure A7 or A53 versions, but instead get replaced with A75/A55, A76/A55 etc as the respective designs make it from high-end to mid-range chips. There are already Snapdragon 690 and Exynos 800-series mid-range chips based on 8nm A77/A55 that fit this description, while Mediatek and Unisoc already tend to use newer cores on older processes.