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Date: Thu, 15 Feb 2024 06:08:57 +0100
From: Christoph Hellwig <hch@lst.de>
To: Robin Murphy <robin.murphy@arm.com>
Cc: Alexander Lobakin <aleksander.lobakin@intel.com>,
	"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>,
	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 v3 2/7] dma: avoid redundant calls for sync
 operations
Message-ID: <20240215050857.GC4861@lst.de>
References: <20240214162201.4168778-1-aleksander.lobakin@intel.com> <20240214162201.4168778-3-aleksander.lobakin@intel.com> <3a9dd580-1977-418f-a3f3-73003dd37710@arm.com>
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On Wed, Feb 14, 2024 at 05:55:23PM +0000, Robin Murphy wrote:
>>   #define DMA_F_PCI_P2PDMA_SUPPORTED     (1 << 0)
>> +#define DMA_F_CAN_SKIP_SYNC		BIT(1)
>
> Yuck, please be consistent - either match the style of the existing code, 
> or change that to BIT(0) as well.

Just don't use BIT() ever.  It doesn't save any typing and creates a
totally pointless mental indirection.

> I guess this was the existing condition from dma_need_sync(), but now it's 
> on a one-off slow path it might be nice to check the sync_sg_* ops as well 
> for completeness, or at least comment that nobody should be implementing 
> those without also implementing the sync_single_* ops.

Implementing only one and not the other doesn't make any sense.  Maybe
a debug check for that is ok, but thing will break badly if they aren't
in sync anyway.