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

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Date:   Fri, 09 Aug 2019 12:43:27 -0700 (PDT)
From:   David Miller <davem@...emloft.net>
To:     Jose.Abreu@...opsys.com
Cc:     netdev@...r.kernel.org, Joao.Pinto@...opsys.com
Subject: Re: [PATCH net-next 01/12] net: stmmac: Get correct timestamp
 values from XGMAC

From: Jose Abreu <Jose.Abreu@...opsys.com>
Date: Fri,  9 Aug 2019 20:36:09 +0200

> +	void __iomem *ioaddr = hw->pcsr;
> +	int count = 0;
> +	u32 value;
> +
> +	do {
> +		if (readl_poll_timeout_atomic(ioaddr + XGMAC_TIMESTAMP_STATUS,
> +					      value, value & XGMAC_TXTSC,
> +					      100, 10000))
> +			break;
> +
> +		*ts = readl(ioaddr + XGMAC_TXTIMESTAMP_NSEC) & XGMAC_TXTSSTSLO;
> +		*ts += readl(ioaddr + XGMAC_TXTIMESTAMP_SEC) * 1000000000ULL;
> +	} while (count++);
> +
> +	if (count)
> +		return 0;
> +	return -EBUSY;

This is a very strange construct, the loop never executes more than once.
Simplified it is essentially:

	if (readl_poll_timeout_atomic(ioaddr + XGMAC_TIMESTAMP_STATUS,
				      value, value & XGMAC_TXTSC,
				      100, 10000))
		return -EBUSY;

	*ts = readl(ioaddr + XGMAC_TXTIMESTAMP_NSEC) & XGMAC_TXTSSTSLO;
	*ts += readl(ioaddr + XGMAC_TXTIMESTAMP_SEC) * 1000000000ULL;
	return 0;

Don't make the code more complicated than it needs to be, there is no
reason to use a loop here.  And using a loop makes it look like the
loop is the polling/timeout construct, when it isn't, because
readl_poll_timeout_atomic() is serving that purpose.