netdev - Re: [PATCH v2 net] net: stmmac: dwmac4: extend timeout for VLAN Tag register busy bit check

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Message-ID: <yzyezokrtcj5pnby4ak5lzrrnqu3y3k45kaibtklwrjn4ivzel@hwf6bgssykna>
Date: Mon, 23 Sep 2024 01:17:49 +0300
From: Serge Semin <fancer.lancer@...il.com>
To: Shenwei Wang <shenwei.wang@....com>
Cc: "David S. Miller" <davem@...emloft.net>, 
	Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, 
	Paolo Abeni <pabeni@...hat.com>, Maxime Coquelin <mcoquelin.stm32@...il.com>, horms@...nel.org, 
	Alexandre Torgue <alexandre.torgue@...s.st.com>, Jose Abreu <joabreu@...opsys.com>, 
	Ong Boon Leong <boon.leong.ong@...el.com>, Wong Vee Khee <vee.khee.wong@...el.com>, 
	Chuah Kim Tatt <kim.tatt.chuah@...el.com>, netdev@...r.kernel.org, linux-stm32@...md-mailman.stormreply.com, 
	linux-arm-kernel@...ts.infradead.org, imx@...ts.linux.dev, linux-imx@....com
Subject: Re: [PATCH v2 net] net: stmmac: dwmac4: extend timeout for VLAN Tag
 register busy bit check

On Wed, Sep 18, 2024 at 02:34:52PM -0500, Shenwei Wang wrote:
> Increase the timeout for checking the busy bit of the VLAN Tag register
> from 10µs to 500ms. This change is necessary to accommodate scenarios
> where Energy Efficient Ethernet (EEE) is enabled.
> 
> Overnight testing revealed that when EEE is active, the busy bit can
> remain set for up to approximately 300ms. The new 500ms timeout provides
> a safety margin.
> 
> Fixes: ed64639bc1e0 ("net: stmmac: Add support for VLAN Rx filtering")
> Signed-off-by: Shenwei Wang <shenwei.wang@....com>
> ---
> Changes in v2:
>  - replace the udelay with readl_poll_timeout per Simon's review.
> 
> ---
>  drivers/net/ethernet/stmicro/stmmac/dwmac4_core.c | 14 +++++++-------
>  1 file changed, 7 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/net/ethernet/stmicro/stmmac/dwmac4_core.c b/drivers/net/ethernet/stmicro/stmmac/dwmac4_core.c
> index a1858f083eef..a0cfa2eaebb4 100644
> --- a/drivers/net/ethernet/stmicro/stmmac/dwmac4_core.c
> +++ b/drivers/net/ethernet/stmicro/stmmac/dwmac4_core.c
> @@ -14,6 +14,7 @@
>  #include <linux/slab.h>
>  #include <linux/ethtool.h>
>  #include <linux/io.h>
> +#include <linux/iopoll.h>
>  #include "stmmac.h"
>  #include "stmmac_pcs.h"
>  #include "dwmac4.h"
> @@ -471,7 +472,7 @@ static int dwmac4_write_vlan_filter(struct net_device *dev,
>  				    u8 index, u32 data)
>  {
>  	void __iomem *ioaddr = (void __iomem *)dev->base_addr;
> -	int i, timeout = 10;
> +	int ret, timeout = 500000; //500ms
>  	u32 val;
> 
>  	if (index >= hw->num_vlan)
> @@ -487,12 +488,11 @@ static int dwmac4_write_vlan_filter(struct net_device *dev,
> 
>  	writel(val, ioaddr + GMAC_VLAN_TAG);
> 
> -	for (i = 0; i < timeout; i++) {
> -		val = readl(ioaddr + GMAC_VLAN_TAG);
> -		if (!(val & GMAC_VLAN_TAG_CTRL_OB))
> -			return 0;
> -		udelay(1);
> -	}

> +	ret = readl_poll_timeout(ioaddr + GMAC_VLAN_TAG, val,
> +				 !(val & GMAC_VLAN_TAG_CTRL_OB),
> +				 1000, timeout);
> +	if (!ret)
> +		return 0;
> 
>  	netdev_err(dev, "Timeout accessing MAC_VLAN_Tag_Filter\n");

1. Just drop the timeout local variable and use the 500000 literal
directly. There is no point in such parametrization especially you
have already added the delay as is.

2. A more traditional, readable and maintainable pattern is the
error-check statement after the call. So seeing you are changing this
part of the method anyway, let's convert it to:

+	ret = readl_poll_timeout(ioaddr + GMAC_VLAN_TAG, val,
+				 !(val & GMAC_VLAN_TAG_CTRL_OB),
+				 1000, timeout);
+	if (ret) {
+		netdev_err(dev, "Timeout accessing MAC_VLAN_Tag_Filter\n");
+		return ret;
+	}
+
+	return 0;

-Serge(y)

> 
> --
> 2.34.1
> 
>