linux-kernel - Re: [PATCH net/next 3/3] net: ethernet: mtk_eth

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Message-ID: <f9bec387-1858-4c79-bb4b-60e744457c9f@lunn.ch>
Date: Sat, 28 Jun 2025 10:13:51 +0200
From: Andrew Lunn <andrew@...n.ch>
To: Daniel Golle <daniel@...rotopia.org>
Cc: Felix Fietkau <nbd@....name>,
	Frank Wunderlich <frank-w@...lic-files.de>,
	Eric Woudstra <ericwouds@...il.com>, Elad Yifee <eladwf@...il.com>,
	Bo-Cun Chen <bc-bocun.chen@...iatek.com>,
	Sky Huang <skylake.huang@...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>,
	Jakub Kicinski <kuba@...nel.org>, 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/next 3/3] net: ethernet: mtk_eth_soc: use genpool
 allocator for SRAM

> +static void *mtk_dma_ring_alloc(struct mtk_eth *eth, size_t size,
> +				dma_addr_t *dma_handle)
> +{
> +	void *dma_ring;
> +
> +	if (WARN_ON(mtk_use_legacy_sram(eth)))
> +		return -ENOMEM;
> +
> +	if (eth->sram_pool) {
> +		dma_ring = (void *)gen_pool_alloc(eth->sram_pool, size);
> +		if (!dma_ring)
> +			return dma_ring;
> +		*dma_handle = gen_pool_virt_to_phys(eth->sram_pool, (unsigned long)dma_ring);

I don't particularly like all the casting backwards and forwards
between unsigned long and void *. These two APIs are not really
compatible with each other. So any sort of wrapping is going to be
messy.

Maybe define a cookie union:

struct mtk_dma_cookie {
	union {
		unsigned long gen_pool;
		void *coherent;
	}
}

Only dma_handle appears to be used by the rest of the code, so only
the _alloc and _free need to know about the union.

	Andrew