linux-kernel - Re: [PATCH net-next v2 01/12] net: stmmac: Get correct timestamp values from XGMAC

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Date:   Tue, 13 Aug 2019 13:57:22 -0700
From:   Jakub Kicinski <jakub.kicinski@...ronome.com>
To:     Jose Abreu <Jose.Abreu@...opsys.com>
Cc:     netdev@...r.kernel.org, Joao Pinto <Joao.Pinto@...opsys.com>,
        Giuseppe Cavallaro <peppe.cavallaro@...com>,
        Alexandre Torgue <alexandre.torgue@...com>,
        "David S. Miller" <davem@...emloft.net>,
        Maxime Coquelin <mcoquelin.stm32@...il.com>,
        linux-stm32@...md-mailman.stormreply.com,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH net-next v2 01/12] net: stmmac: Get correct timestamp
 values from XGMAC

On Mon, 12 Aug 2019 11:44:00 +0200, Jose Abreu wrote:
> TX Timestamp in XGMAC comes from MAC instead of descriptors. Implement
> this in a new callback.
> 
> Also, RX Timestamp in XGMAC must be cheked against corruption and we need
> a barrier to make sure that descriptor fields are read correctly.
> 
> Changes from v1:
> 	- Rework the get timestamp function (David)
> 
> Signed-off-by: Jose Abreu <joabreu@...opsys.com>

The barrier sounds like it might be a bug fix, does it occur in he wild?

> @@ -113,13 +119,11 @@ static int dwxgmac2_get_rx_timestamp_status(void *desc, void *next_desc,
>  	unsigned int rdes3 = le32_to_cpu(p->des3);
>  	int ret = -EBUSY;
>  
> -	if (likely(rdes3 & XGMAC_RDES3_CDA)) {
> +	if (likely(rdes3 & XGMAC_RDES3_CDA))
>  		ret = dwxgmac2_rx_check_timestamp(next_desc);
> -		if (ret)
> -			return ret;
> -	}
> -
> -	return ret;
> +	if (!ret)
> +		return 1;
> +	return 0;

nit:

	return !ret;

>  }
>  
>  static void dwxgmac2_init_rx_desc(struct dma_desc *p, int disable_rx_ic,