linux-kernel - Re: [PATCH 2/2] xen: swiotlb: Implement map

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Message-ID: <aBwvrLKD_VJapYkB@infradead.org>
Date: Wed, 7 May 2025 21:14:36 -0700
From: Christoph Hellwig <hch@...radead.org>
To: Stefano Stabellini <sstabellini@...nel.org>
Cc: John Ernberg <john.ernberg@...ia.se>, Juergen Gross <jgross@...e.com>,
	Oleksandr Tyshchenko <oleksandr_tyshchenko@...m.com>,
	Catalin Marinas <catalin.marinas@....com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"xen-devel@...ts.xenproject.org" <xen-devel@...ts.xenproject.org>,
	"iommu@...ts.linux.dev" <iommu@...ts.linux.dev>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"imx@...ts.linux.dev" <imx@...ts.linux.dev>,
	Christoph Hellwig <hch@...radead.org>
Subject: Re: [PATCH 2/2] xen: swiotlb: Implement map_resource callback

On Wed, May 07, 2025 at 04:09:15PM -0700, Stefano Stabellini wrote:
> > This mapping is not for a RAM backed address. In the eDMA case for the 
> > iMX8QXP the `phys` coming in here is the address of a register.
> 
> Ok, this information is important :-)
> 
> I am not certain whether the map_resource interface can only be called
> for MMIO addresses or if it can also be called for RAM-backed addresses
> with a size > PAGE_SIZE. In the latter case, we could run into the issue
> I was describing.

map_resource is intended for MMIO regions, although those could be >
PAGE_SIZE.  It must not be called on RAM.