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Date: Thu, 19 Dec 2024 06:47:01 +0100
From: Christoph Hellwig <hch@lst.de>
To: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Cc: Damien Le Moal <dlemoal@kernel.org>, linux-nvme@lists.infradead.org,
	Christoph Hellwig <hch@lst.de>, Keith Busch <kbusch@kernel.org>,
	Sagi Grimberg <sagi@grimberg.me>, linux-pci@vger.kernel.org,
	Krzysztof =?utf-8?Q?Wilczy=C5=84ski?= <kw@linux.com>,
	Kishon Vijay Abraham I <kishon@kernel.org>,
	Bjorn Helgaas <bhelgaas@google.com>,
	Lorenzo Pieralisi <lpieralisi@kernel.org>,
	Rick Wertenbroek <rick.wertenbroek@gmail.com>,
	Niklas Cassel <cassel@kernel.org>
Subject: Re: [PATCH v4 17/18] nvmet: New NVMe PCI endpoint target driver
Message-ID: <20241219054701.GC18853@lst.de>
References: <20241212113440.352958-1-dlemoal@kernel.org> <20241212113440.352958-18-dlemoal@kernel.org> <20241217085355.y6bqqisqbr5kbxkl@thinkpad> <4015e54a-54a5-4ac7-ae1c-3d2fb935b20f@kernel.org> <20241217164149.vuqwtthlykn7bobj@thinkpad>
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User-Agent: Mutt/1.5.17 (2007-11-01)

On Tue, Dec 17, 2024 at 10:11:49PM +0530, Manivannan Sadhasivam wrote:
> 'iomem' is just a token that is used by sparse tool to verify correctness of
> MMIO address handling.

That is true, but we don't have the token just for fun, but because iomem
needs to be treated differently.

> I know that the memory here is returned by
> dma_alloc_coherent() and is not exactly a MMIO. But since you are using
> READ_ONCE() and le32_to_cpu() on these addresses, I thought about suggesting
> readl/writel that does exactly the same internally. If you do not need ordering,
> then you can use relaxed variants as well.

No, using readl/writel on dma_alloc_coherent buffers is simply wrong.