linux-kernel - Re: [PATCH net-next v3 2/7] dma: avoid redundant calls for sync operations

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Date: Mon, 19 Feb 2024 13:49:10 +0100
From: Alexander Lobakin <aleksander.lobakin@...el.com>
To: Robin Murphy <robin.murphy@....com>
CC: "David S. Miller" <davem@...emloft.net>, Eric Dumazet
	<edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, Paolo Abeni
	<pabeni@...hat.com>, Christoph Hellwig <hch@....de>, Marek Szyprowski
	<m.szyprowski@...sung.com>, Joerg Roedel <joro@...tes.org>, Will Deacon
	<will@...nel.org>, Greg Kroah-Hartman <gregkh@...uxfoundation.org>, "Rafael
 J. Wysocki" <rafael@...nel.org>, Magnus Karlsson <magnus.karlsson@...el.com>,
	Maciej Fijalkowski <maciej.fijalkowski@...el.com>, Alexander Duyck
	<alexanderduyck@...com>, <bpf@...r.kernel.org>, <netdev@...r.kernel.org>,
	<iommu@...ts.linux.dev>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH net-next v3 2/7] dma: avoid redundant calls for sync
 operations

From: Robin Murphy <robin.murphy@....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

> 
>> +        /*
>> +         * Assume that when ``DMA_F_CAN_SKIP_SYNC`` is advertised,
>> +         * the conditions for synchronizing are the same as with
>> +         * the direct DMA.
>> +         */
>> +        dev->dma_skip_sync = dev_is_dma_coherent(dev);
>> +    else
>> +        dev->dma_skip_sync = false;
>> +}
>> +#endif /* CONFIG_DMA_NEED_SYNC */

[...]

Thanks,
Olek