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Date: Thu, 9 May 2024 14:01:49 +0200
From: Christoph Hellwig <hch@lst.de>
To: Alexander Lobakin <aleksander.lobakin@intel.com>
Cc: Marek Szyprowski <m.szyprowski@samsung.com>,
	Christoph Hellwig <hch@lst.de>, Eric Dumazet <edumazet@google.com>,
	Jakub Kicinski <kuba@kernel.org>,
	Robin Murphy <robin.murphy@arm.com>, Joerg Roedel <joro@8bytes.org>,
	Will Deacon <will@kernel.org>,
	"Rafael J. Wysocki" <rafael@kernel.org>,
	Magnus Karlsson <magnus.karlsson@intel.com>,
	nex.sw.ncis.osdt.itp.upstreaming@intel.com, bpf@vger.kernel.org,
	netdev@vger.kernel.org, iommu@lists.linux.dev,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH v6 2/7] dma: avoid redundant calls for sync operations
Message-ID: <20240509120149.GA11327@lst.de>
References: <20240507112026.1803778-1-aleksander.lobakin@intel.com> <CGME20240507112115eucas1p117bc01652d4cdbe810de841830227f47@eucas1p1.samsung.com> <20240507112026.1803778-3-aleksander.lobakin@intel.com> <46160534-5003-4809-a408-6b3a3f4921e9@samsung.com> <b4632761-3ec6-4070-a60e-b74c1bfdd579@intel.com>
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User-Agent: Mutt/1.5.17 (2007-11-01)

On Thu, May 09, 2024 at 01:44:37PM +0200, Alexander Lobakin wrote:
> If I remember correctly, *all* device drivers which use DMA *must* call
> dma_set_*mask() on probe. That's why we added it there and didn't care.
> Alternatively, if it really breaks a lot of drivers, we can set
> dma_need_sync = true by default before the driver probing. I thought of
> this, but the correct approach would be to call dma_set_*mask() from the
> respective drivers.

No, we default to 32-bit DMA for a lot of busses for historical reasons,
especially platform devices.