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Date: Mon, 26 Feb 2024 15:45:44 +0000
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Subject: Re: [PATCH net-next v3 2/7] dma: avoid redundant calls for sync
 operations
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>,
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 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
References: <20240214162201.4168778-1-aleksander.lobakin@intel.com>
 <20240214162201.4168778-3-aleksander.lobakin@intel.com>
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 <4d2678be-e36c-4726-83a5-ae9a3a0def55@intel.com>
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From: Robin Murphy <robin.murphy@arm.com>
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On 19/02/2024 12:49 pm, Alexander Lobakin wrote:
> From: Robin Murphy <robin.murphy@arm.com>
> Date: Wed, 14 Feb 2024 17:55:23 +0000
> 
>> On 2024-02-14 4:21 pm, Alexander Lobakin wrote:
> 
> [...]
> 
>>> +        /*
>>> +         * Synchronization is not possible when none of DMA sync ops
>>> +         * is set. This check precedes the below one as it disables
>>> +         * the synchronization unconditionally.
>>> +         */
>>> +        dev->dma_skip_sync = true;
>>> +    else if (ops->flags & DMA_F_CAN_SKIP_SYNC)
>>
>> Personally I'd combine this into the dma-direct condition.
> 
> Please read the code comment a couple lines above :D

And my point is that that logic is not actually useful, since it would 
be nonsensical for ops to set DMA_F_CAN_SKIP_SYNC if they don't even 
implement sync ops anyway.

If the intent of DMA_F_CAN_SKIP_SYNC is to mean "behaves like 
dma-direct", then "if (dma_map_direct(...) || ops->flags & 
DMA_F_CAN_SKIP_SYNC)" is an entirely logical and expected condition.

Thanks,
Robin.