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Date: Wed, 18 Sep 2024 09:16:32 +0100
From: Simon Horman <horms@kernel.org>
To: Shenwei Wang <shenwei.wang@nxp.com>
Cc: "David S. Miller" <davem@davemloft.net>,
	Eric Dumazet <edumazet@google.com>,
	Jakub Kicinski <kuba@kernel.org>, Paolo Abeni <pabeni@redhat.com>,
	Maxime Coquelin <mcoquelin.stm32@gmail.com>,
	Alexandre Torgue <alexandre.torgue@foss.st.com>,
	Jose Abreu <joabreu@synopsys.com>,
	Wong Vee Khee <vee.khee.wong@intel.com>,
	Ong Boon Leong <boon.leong.ong@intel.com>,
	Chuah Kim Tatt <kim.tatt.chuah@intel.com>, netdev@vger.kernel.org,
	linux-stm32@st-md-mailman.stormreply.com,
	linux-arm-kernel@lists.infradead.org, imx@lists.linux.dev,
	linux-imx@nxp.com
Subject: Re: [PATCH net] net: stmmac: dwmac4: extend timeout for VLAN Tag
 register busy bit check
Message-ID: <20240918081632.GU167971@kernel.org>
References: <20240917164206.414714-1-shenwei.wang@nxp.com>
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In-Reply-To: <20240917164206.414714-1-shenwei.wang@nxp.com>

On Tue, Sep 17, 2024 at 11:42:06AM -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.
> 
> This modification does not impact normal success path, as the function
> typically returns within 1µs in non-EEE scenarios. The extended timeout
> only affects the failure path.
> 
> Fixes: ed64639bc1e0 ("net: stmmac: Add support for VLAN Rx filtering")
> Signed-off-by: Shenwei Wang <shenwei.wang@nxp.com>

Hi Shenwei Wang,

It looks like this function now uses udelay() to busy-wait for up to 500ms.
But 500ms, or indeed 300ms, seems like a long time to tie down a core.  I
wonder if some other sort of mechanism, f.e. involving msleep or delayed
work, should be considered.

...