linux-kernel - Re: [TECH TOPIC] Reaching consensus on CONFIG

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Message-ID: <cc027fae-8d34-41ca-bd35-569c415fc657@microchip.com>
Date: Fri, 19 Sep 2025 16:41:26 +0200
From: Nicolas Ferre <nicolas.ferre@...rochip.com>
To: Geert Uytterhoeven <geert@...ux-m68k.org>, Arnd Bergmann <arnd@...db.de>
CC: Jason Gunthorpe <jgg@...dia.com>, <ksummit@...ts.linux.dev>,
	<linux-kernel@...r.kernel.org>, <linux-arm-kernel@...ts.infradead.org>,
	<linuxppc-dev@...ts.ozlabs.org>, <linux-mips@...r.kernel.org>,
	<linux-mm@...ck.org>, <imx@...ts.linux.dev>, Christophe Leroy
	<christophe.leroy@...roup.eu>, Richard Weinberger <richard@....at>, Lucas
 Stach <l.stach@...gutronix.de>, Linus Walleij <linus.walleij@...aro.org>,
	Geert Uytterhoeven <geert+renesas@...der.be>, Ankur Arora
	<ankur.a.arora@...cle.com>, David Hildenbrand <david@...hat.com>, Mike
 Rapoport <rppt@...nel.org>, Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
	Matthew Wilcox <willy@...radead.org>, Andrew Morton
	<akpm@...ux-foundation.org>, "Liam R. Howlett" <Liam.Howlett@...cle.com>,
	Vlastimil Babka <vbabka@...e.cz>, Suren Baghdasaryan <surenb@...gle.com>, Ira
 Weiny <ira.weiny@...el.com>, Nishanth Menon <nm@...com>,
	Heiko Stübner <heiko@...ech.de>, Alexander Sverdlin
	<alexander.sverdlin@...il.com>, "Chester A. Unal"
	<chester.a.unal@...nc9.com>, Sergio Paracuellos
	<sergio.paracuellos@...il.com>, Andreas Larsson <andreas@...sler.com>
Subject: Re: [TECH TOPIC] Reaching consensus on CONFIG_HIGHMEM phaseout

Hi Geert,

On 19/09/2025 at 09:17, Geert Uytterhoeven wrote:
> Hi Arnd,
> 
> On Thu, 18 Sept 2025 at 15:13, Arnd Bergmann <arnd@...db.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:
>>>
>>>> I'm still collecting information about which of the remaining highmem
>>>> users plan to keep updating their kernels and for what reason.
>>>
>>> On this topic of removing some parts of highmem, can we say goodbye to
>>> kmap_high_get()? Only ARM uses it and only for
>>> !cache_is_vipt_nonaliasing() systems.
>>
>> Good idea. I think we are almost there, just need to verify that
>> there is actually no impact for existing users. I already knew
>> that there is very little highmem usage on ARMv6 and earlier, but
>> I tried to recheck all platforms that might be affected:
> 
>> * 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?

For sam9x75:
- DDR2
- DDR3  (DLL Off/On mode)
- DDR3L (DLL Off/On mode)

For (older) sam9x60:
- LPDDR1
- DDR2
- SDRAM & Mobile SDRAM
> 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?
No, in fact we address 256 M Bytes max on sam9x60 and sam9x75 as well.

Regards,
   Nicolas