netdev - Re: [PATCH net v1] net: stmmac: TSO: Fix unbalanced DMA map/unmap for non-paged SKB data

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Message-ID: <20241203111637.000023fe@gmail.com>
Date: Tue, 3 Dec 2024 11:16:37 +0800
From: Furong Xu <0x1207@...il.com>
To: Jakub Kicinski <kuba@...nel.org>
Cc: Jon Hunter <jonathanh@...dia.com>, netdev@...r.kernel.org,
 linux-stm32@...md-mailman.stormreply.com,
 linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
 Alexandre Torgue <alexandre.torgue@...s.st.com>, Jose Abreu
 <joabreu@...opsys.com>, "David S. Miller" <davem@...emloft.net>, Eric
 Dumazet <edumazet@...gle.com>, Paolo Abeni <pabeni@...hat.com>, Maxime
 Coquelin <mcoquelin.stm32@...il.com>, xfr@...look.com, Suraj Jaiswal
 <quic_jsuraj@...cinc.com>, Thierry Reding <treding@...dia.com>,
 "linux-tegra@...r.kernel.org" <linux-tegra@...r.kernel.org>
Subject: Re: [PATCH net v1] net: stmmac: TSO: Fix unbalanced DMA map/unmap
 for non-paged SKB data

On Mon, 2 Dec 2024 18:34:25 -0800, Jakub Kicinski <kuba@...nel.org> wrote:

> On Tue, 3 Dec 2024 10:03:31 +0800 Furong Xu wrote:
> > I requested Jon to provide more info about "Tx DMA map failed" in previous
> > reply, and he does not respond yet.  
> 
> What does it mean to provide "more info" about a print statement from
> the driver? Is there a Kconfig which he needs to set to get more info?
> Perhaps you should provide a debug patch he can apply on his tree, that
> will print info about (1) which buffer mapping failed (head or frags);
> (2) what the physical address was of the buffer that couldn't be mapped.

A debug patch to print info about buffer makes no sense here.
Both Tegra186 Jetson TX2(tegra186-p2771-0000) and Tegra194 Jetson AGX Xavier
(tegra194-p2972-0000) enable IOMMU/SMMU for stmmac in its device-tree node,
buffer info should be investigated with detailed IOMMU/SMMU debug info from
drivers/iommu/arm/arm-smmu/arm-smmu-nvidia.c together.

I am not an expert in IOMMU, so I cannot help more.

Without the help from Jon, our only choice is revert as you said.

Thanks.