netdev - Re: [PATCH net 1/2] net: stmmac: fix taprio schedule configuration

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Date:   Tue, 12 Jan 2021 18:29:17 -0800
From:   Jakub Kicinski <kuba@...nel.org>
To:     Yannick Vignon <yannick.vignon@....nxp.com>
Cc:     Giuseppe Cavallaro <peppe.cavallaro@...com>,
        Alexandre Torgue <alexandre.torgue@...com>,
        Jose Abreu <joabreu@...opsys.com>,
        "David S. Miller" <davem@...emloft.net>, netdev@...r.kernel.org,
        Yannick Vignon <yannick.vignon@....com>
Subject: Re: [PATCH net 1/2] net: stmmac: fix taprio schedule configuration

On Tue, 12 Jan 2021 18:24:56 +0100 Yannick Vignon wrote:
> From: Yannick Vignon <yannick.vignon@....com>
> 
> When configuring a 802.1Qbv schedule through the tc taprio qdisc on an NXP
> i.MX8MPlus device, the effective cycle time differed from the requested one
> by N*96ns, with N number of entries in the Qbv Gate Control List. This is
> because the driver was adding a 96ns margin to each interval of the GCL,
> apparently to account for the IPG. The problem was observed on NXP
> i.MX8MPlus devices but likely affected all devices relying on the same
> configuration callback (dwmac 4.00, 4.10, 5.10 variants).
> 
> Fix the issue by removing the margins, and simply setup the MAC with the
> provided cycle time value. This is the behavior expected by the user-space
> API, as altering the Qbv schedule timings would break standards conformance.
> This is also the behavior of several other Ethernet MAC implementations
> supporting taprio, including the dwxgmac variant of stmmac.
> 
> Signed-off-by: Yannick Vignon <yannick.vignon@....com>

Thanks for the patches, could you repost and include appropriate Fixes
tags?

https://www.kernel.org/doc/html/latest/process/submitting-patches.html#describe-your-changes

> +	u32 ctrl;
> 	int i, ret = 0x0;

Please keep the variable declaration lines sorted longest to shortest
in both patches.