netdev - Re: [PATCH net v2] net: ethernet: mtk_eth

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Message-ID: <20250429144220.5d22fc1f@kernel.org>
Date: Tue, 29 Apr 2025 14:42:20 -0700
From: Jakub Kicinski <kuba@...nel.org>
To: Daniel Golle <daniel@...rotopia.org>
Cc: Chad Monroe <chad@...roe.io>, Felix Fietkau <nbd@....name>, Bc-Bocun
 Chen <bc-bocun.chen@...iatek.com>, Sean Wang <sean.wang@...iatek.com>,
 Lorenzo Bianconi <lorenzo@...nel.org>, Andrew Lunn <andrew+netdev@...n.ch>,
 "David S. Miller" <davem@...emloft.net>, Eric Dumazet
 <edumazet@...gle.com>, Paolo Abeni <pabeni@...hat.com>, Matthias Brugger
 <matthias.bgg@...il.com>, AngeloGioacchino Del Regno
 <angelogioacchino.delregno@...labora.com>, netdev@...r.kernel.org,
 linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
 linux-mediatek@...ts.infradead.org
Subject: Re: [PATCH net v2] net: ethernet: mtk_eth_soc: fix SER panic with
 4GB+ RAM

On Sun, 27 Apr 2025 02:05:44 +0100 Daniel Golle wrote:
> +		if (MTK_HAS_CAPS(eth->soc->caps, MTK_36BIT_DMA)) {
> +			if (unlikely(dma_addr == DMA_MAPPING_ERROR))
> +				addr64 = FIELD_GET(RX_DMA_ADDR64_MASK,
> +						   rxd->rxd2);
> +			else
> +				addr64 = RX_DMA_PREP_ADDR64(dma_addr);

I guess it's correct but FWIW it reads slightly weird that in one
branch we use FIELD_GET() and in the other "PREP". I get that the
macros are a bit complicated but to the reader its not obvious whether
the value stored in addr64 is expected to be shifted or not 🤷️

> + rxd->rxd2 = RX_DMA_PREP_PLEN0(ring->buf_size) | addr64;