linux-kernel - Re: [PATCH][linux-next] net: enetc: unmap DMA in enetc_send

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Date:   Wed, 20 Oct 2021 15:23:12 -0700
From:   Jakub Kicinski <kuba@...nel.org>
To:     Claudiu Manoil <claudiu.manoil@....com>,
        Tim Gardner <tim.gardner@...onical.com>
Cc:     "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "David S. Miller" <davem@...emloft.net>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Po Liu <po.liu@....com>
Subject: Re: [PATCH][linux-next] net: enetc: unmap DMA in enetc_send_cmd()

On Tue, 19 Oct 2021 19:47:17 +0000 Claudiu Manoil wrote:
> > I am curious why you do not need to call dma_sync_single_for_device()
> > before enetc_send_cmd()
> > in order to flush the contents of CPU cache to RAM. Is it because
> > __GFP_DMA marks
> > that page as uncached ? Or is it because of the SOC this runs on ?
> >   
> 
> Not sure how it works like this, but I think dma_alloc_coherent() should have
> been used here instead of the kmalloc + dma_map scheme.

Using dma_alloc_coherent() seems simpler and more correct, 
let's do that instead.