linux-kernel - Re: [RFC] ITS fails to allocate on rk3568/rk3566

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Date:   Tue, 13 Apr 2021 16:51:12 +0100
From:   Marc Zyngier <maz@...nel.org>
To:     Peter Geis <pgwipeout@...il.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        "open list:ARM/Rockchip SoC..." <linux-rockchip@...ts.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [RFC] ITS fails to allocate on rk3568/rk3566

On Tue, 13 Apr 2021 16:03:51 +0100,
Peter Geis <pgwipeout@...il.com> wrote:
> 
> On Tue, Apr 13, 2021 at 10:01 AM Marc Zyngier <maz@...nel.org> wrote:

[...]

> > What happens if you hack all the allocations to happen in the low 4GB
> > of the PA space?
> 
> It seems to work correctly.
> The downstream hacks used GFP_DMA32 which gets discarded by
> kmalloc_fix_flags on certain allocations.
> Switching to GFP_DMA seems to have satisfied it, but it feels wrong
> using this code.
> Need to check the corner cases to make sure I'm not missing something.

The problem is that GFP_DMA doesn't always mean the same thing.
Overall, we need to hear from Rockchip about the exact nature of the
problem, and then we *may* be able to work something out.

I'd also like to understand whether it is broken because you happen to
have pre-release silicon that will never make it into the wild, or if
this is the real thing that is going to ship on millions of devices.

Thanks,

	M.

-- 
Without deviation from the norm, progress is not possible.