linux-kernel - Re: [PATCH v3 0/5] enhance DMA CMA on x86

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Message-ID: <542B5DC2.8020806@hurleysoftware.com>
Date:	Tue, 30 Sep 2014 21:49:54 -0400
From:	Peter Hurley <peter@...leysoftware.com>
To:	Thomas Gleixner <tglx@...utronix.de>
CC:	Akinobu Mita <akinobu.mita@...il.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Marek Szyprowski <m.szyprowski@...sung.com>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	David Woodhouse <dwmw2@...radead.org>,
	Don Dutile <ddutile@...hat.com>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>, Andi Kleen <andi@...stfloor.org>,
	x86@...nel.org, iommu@...ts.linux-foundation.org,
	Greg KH <greg@...ah.com>
Subject: Re: [PATCH v3 0/5] enhance DMA CMA on x86

On 09/30/2014 07:45 PM, Thomas Gleixner wrote:
> Whether the proposed patchset is the correct solution to support it is
> a completely different question.

This patchset has been in mainline since 3.16 and has already caused
regressions, so the question of whether this is the correct solution has
already been answered.

> So either you stop this right now and help Akinobu to find the proper
> solution 

If this is only a test platform for ARM parts then I don't think it
unreasonable to suggest forking x86 swiotlb support into a iommu=cma
selector that gets DMA mapping working for this test platform and doesn't
cause a bunch of breakage.

Which is different than if the plan is to ship production units for x86;
then a general purpose solution will be required.

As to the good design of a general purpose solution for allocating and
mapping huge order pages, you are certainly more qualified to help Akinobu
than I am.

Regards,
Peter Hurley

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