linux-kernel - Re: [PATCH v6 2/7] dma: avoid redundant calls for sync operations

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Date: Thu, 9 May 2024 14:01:49 +0200
From: Christoph Hellwig <hch@....de>
To: Alexander Lobakin <aleksander.lobakin@...el.com>
Cc: Marek Szyprowski <m.szyprowski@...sung.com>,
	Christoph Hellwig <hch@....de>, Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>,
	Robin Murphy <robin.murphy@....com>, Joerg Roedel <joro@...tes.org>,
	Will Deacon <will@...nel.org>,
	"Rafael J. Wysocki" <rafael@...nel.org>,
	Magnus Karlsson <magnus.karlsson@...el.com>,
	nex.sw.ncis.osdt.itp.upstreaming@...el.com, bpf@...r.kernel.org,
	netdev@...r.kernel.org, iommu@...ts.linux.dev,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v6 2/7] dma: avoid redundant calls for sync operations

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.