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Date:   Mon, 11 Jul 2022 09:09:55 -0700
From:   Christoph Hellwig <hch@infradead.org>
To:     Li Chen <me@linux.beauty>
Cc:     Christoph Hellwig <hch@infradead.org>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Will Deacon <will@kernel.org>,
        Rob Herring <robh+dt@kernel.org>,
        Frank Rowand <frowand.list@gmail.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        linux-arm-kernel <linux-arm-kernel@lists.infradead.org>,
        linux-kernel <linux-kernel@vger.kernel.org>,
        devicetree <devicetree@vger.kernel.org>,
        linux-mm <linux-mm@kvack.org>
Subject: Re: [PATCH 0/4] add struct page and Direct I/O support to reserved
 memory
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 <181ee01d384.b809bd01412268.496620746959082770@linux.beauty>
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On Tue, Jul 12, 2022 at 12:05:06AM +0800, Li Chen wrote:
> My use case has been stated in the cover letter, but our driver is not ready for upstream yet.

Which means we can't review the use case.  I'd suggest you come back
when you submit your driver.

> With DMA allocator, we can access buffer in kernel space, not userspace, however, this patch

Take a look at dma_mmap_* on how to map DMA coherent allocations to
usersapce.  This is of course easily possible.