Re: [TECH TOPIC] Reaching consensus on CONFIG_HIGHMEM phaseout

Arnd Bergmann
2025-09-19T14:22:54Z

On Fri, Sep 19, 2025, at 09:17, Geert Uytterhoeven wrote:
> On Thu, 18 Sept 2025 at 15:13, Arnd Bergmann <arnd@arndb.de> wrote:
>> On Wed, Sep 17, 2025, at 14:59, Jason Gunthorpe wrote:
>> > On Tue, Sep 09, 2025 at 11:23:37PM +0200, Arnd Bergmann wrote:
>
>> * Microchip SAM9x7 is the newest ARMv5 chip, clearly does
>> get kernel updates, and the only one I can think of with
>> DDR3 support, but seems to be limited to 256MB total memory.
>
> Are they limited to DDR3?
>
> IIRC, someone (you? ;-) told me at ELCE that Microchip keeps on spinning
> new variants of old SoCs, to accommodate the changing DDR landscape
> and market. So perhaps they also accept larger RAM sizes?

Yes, that was me. The previous SAM9x60 was released in 2020
and I think that one was an upgrade to a smaller process node,
raising the clock frequency to 600MHz and adding more modern
peripherals, but I see now that this used the same SDRAM/LPDDR/DDR2
memory controller as previous chips, with a limit of 128MB
total DRAM.

SAM9X7 in 2023 added DDR3 mode with up to 256MB according to
the datasheet, no idea why they chose not to support more,
since a 32-bit wide DDR3 bus should allow up to 1GB with two
256Mbit x16 chips that are widely available, or even more using
expensive 512Mbit x16 or 1Gbit x8 chips.

Arnd