linux-kernel - Re: [PATCH] riscv: make ZONE_DMA32 optional

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Message-ID: <37cfd941-f51d-44d8-8283-389ea8d53e69@codethink.co.uk>
Date: Mon, 7 Oct 2024 13:17:01 +0100
From: Ben Dooks <ben.dooks@...ethink.co.uk>
To: Vladimir Kondratiev <Vladimir.Kondratiev@...ileye.com>,
 Alexandre Ghiti <alex@...ti.fr>, Paul Walmsley <paul.walmsley@...ive.com>,
 Palmer Dabbelt <palmer@...belt.com>, Albert Ou <aou@...s.berkeley.edu>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
 "linux-riscv@...ts.infradead.org" <linux-riscv@...ts.infradead.org>,
 "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
 "linux-mm@...ck.org" <linux-mm@...ck.org>
Subject: Re: [PATCH] riscv: make ZONE_DMA32 optional

On 06/10/2024 11:44, Vladimir Kondratiev wrote:
>> I'm wondering how distro kernels will deal with that since some
>> platforms will need the ZONE_DMA32 and some others will break when
>> enabled as you have shown.
> 
> I agree platforms with no ZONE_DMA32 is non-portable,
> to address this I will add dependency on NONPORTABLE and re-submit
> shortly. Thanks for pointing that.

So the last time I got to looking at this, the SoC had no memory
in the 32bit space and all the on-chip IP blocks where all 64bit
DMA capable.

The only thing we didn't sort out was anything connected by the DW
PCIe core, but we think that could use an inbound  translation window.

However, software wise we didn't have the time to try and either
hack something into the kernel or write some form of IOMMU for the 
inbound translation unit. We just removed the warnings to get the
initial testing through.

>> Is there a way to make it optional at runtime instead?
> Unfortunately no, or at least I see no way to do so
> 
> Thanks, Vladimir
> _______________________________________________
> linux-riscv mailing list
> linux-riscv@...ts.infradead.org
> http://lists.infradead.org/mailman/listinfo/linux-riscv
> 

-- 
Ben Dooks				http://www.codethink.co.uk/
Senior Engineer				Codethink - Providing Genius

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