linux-kernel - Re: [PATCH 4/4] arm64: gicv3: its: Increase FORCE_MAX

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Message-ID: <20150520164858.GD29424@e104818-lin.cambridge.arm.com>
Date:	Wed, 20 May 2015 17:48:59 +0100
From:	Catalin Marinas <catalin.marinas@....com>
To:	Robert Richter <robert.richter@...iumnetworks.com>
Cc:	Marc Zyngier <marc.zyngier@....com>,
	Robert Richter <rric@...nel.org>,
	Will Deacon <will.deacon@....com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Tirumalesh Chalamarla <tchalamarla@...ium.com>,
	Radha Mohan Chintakuntla <rchintakuntla@...ium.com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH 4/4] arm64: gicv3: its: Increase FORCE_MAX_ZONEORDER for
 Cavium ThunderX

On Wed, May 20, 2015 at 02:31:59PM +0200, Robert Richter wrote:
> On 20.05.15 13:22:13, Marc Zyngier wrote:
> > On Tue, 12 May 2015 18:24:16 +0100
> > Will Deacon <will.deacon@....com> wrote:
> > > On Tue, May 12, 2015 at 05:20:49PM +0100, Robert Richter wrote:
> > > > On 12.05.15 13:30:57, Will Deacon wrote:
> 
> > > > For allocation of 16MB cont. phys mem of a defconfig kernel (4KB
> > > > default pagesize) I see this different approaches:
> > > 
> > > 16MB sounds like an awful lot. Is this because you have tonnes of MSIs or
> > > a sparse DeviceID space or both?
> > 
> > That's probably due to the sparseness of the DeviceID space. With some
> > form of bridge number encoded on top of the BFD number, the device
> > table is enormous, and I don't see a nice way to avoid it...
> 
> Right. At the momement out of 21 bits (16MB) we currently have 2 spare
> bits, which reduces the actually size used to 4MB. Though, for the
> current cpu model we can reduce it at least to 8MB total.
> 
> I will come up with an additional patch setting this to 8MB.
> 
> As said before, I also write on a patch to use CMA.

Can we not reserve a chunk of memory and pass the information to the
kernel via DT (/memreserve/ and a new GIC-specific binding)?

-- 
Catalin
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