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Date: Mon, 29 Jan 2024 07:11:36 +0100
From: Christoph Hellwig <hch@lst.de>
To: Alexander Lobakin <aleksander.lobakin@intel.com>
Cc: "David S. Miller" <davem@davemloft.net>,
	Eric Dumazet <edumazet@google.com>,
	Jakub Kicinski <kuba@kernel.org>, Paolo Abeni <pabeni@redhat.com>,
	Christoph Hellwig <hch@lst.de>,
	Marek Szyprowski <m.szyprowski@samsung.com>,
	Robin Murphy <robin.murphy@arm.com>, Joerg Roedel <joro@8bytes.org>,
	Will Deacon <will@kernel.org>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	"Rafael J. Wysocki" <rafael@kernel.org>,
	Magnus Karlsson <magnus.karlsson@intel.com>,
	Maciej Fijalkowski <maciej.fijalkowski@intel.com>,
	Alexander Duyck <alexanderduyck@fb.com>, bpf@vger.kernel.org,
	netdev@vger.kernel.org, iommu@lists.linux.dev,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH net-next 1/7] dma: compile-out DMA sync op calls when
 not used
Message-ID: <20240129061136.GD19258@lst.de>
References: <20240126135456.704351-1-aleksander.lobakin@intel.com> <20240126135456.704351-2-aleksander.lobakin@intel.com>
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In-Reply-To: <20240126135456.704351-2-aleksander.lobakin@intel.com>
User-Agent: Mutt/1.5.17 (2007-11-01)

On Fri, Jan 26, 2024 at 02:54:50PM +0100, Alexander Lobakin wrote:
> Some platforms do have DMA, but DMA there is always direct and coherent.
> Currently, even on such platforms DMA sync operations are compiled and
> called.
> Add a new hidden Kconfig symbol, DMA_NEED_SYNC, and set it only when
> either sync operations are needed or there is DMA ops or swiotlb
> enabled. Set dma_need_sync() and dma_skip_sync() (stub for now)
> depending on this symbol state and don't call sync ops when
> dma_skip_sync() is true.
> The change allows for future optimizations of DMA sync calls depending
> on compile-time or runtime conditions.

So the idea of compiling out the calls sounds fine to me.  But what
is the point of the extra indirection through the __-prefixed calls?

And if we need that (please document it in the commit log), please
make the wrappers proper inline functions and not macros.