netdev - Re: [PATCH v2] net: Google gve: Remove dma

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Date:   Fri, 03 Jan 2020 12:41:17 -0800 (PST)
From:   David Miller <davem@...emloft.net>
To:     liran.alon@...cle.com
Cc:     csully@...gle.com, netdev@...r.kernel.org, sagis@...gle.com,
        jonolson@...gle.com, yangchun@...gle.com, lrizzo@...gle.com,
        adisuresh@...gle.com, eric.dumazet@...il.com, si-wei.liu@...cle.com
Subject: Re: [PATCH v2] net: Google gve: Remove dma_wmb() before ringing
 doorbell

From: Liran Alon <liran.alon@...cle.com>
Date: Fri,  3 Jan 2020 18:44:59 +0200

> Current code use dma_wmb() to ensure Rx/Tx descriptors are visible
> to device before writing to doorbell.
> 
> However, these dma_wmb() are wrong and unnecessary. Therefore,
> they should be removed.
> 
> iowrite32be() called from gve_rx_write_doorbell()/gve_tx_put_doorbell()
> should guaratee that all previous writes to WB/UC memory is visible to
> device before the write done by iowrite32be().
> 
> E.g. On ARM64, iowrite32be() calls __iowmb() which expands to dma_wmb()
> and only then calls __raw_writel().
> 
> Reviewed-by: Si-Wei Liu <si-wei.liu@...cle.com>
> Signed-off-by: Liran Alon <liran.alon@...cle.com>

Applied, thank you.