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

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Message-ID: <ea30ed46-b0b5-4ade-8267-f6f4a45fdd5d@lunn.ch>
Date: Sun, 29 Jun 2025 20:23:36 +0200
From: Andrew Lunn <andrew@...n.ch>
To: Daniel Golle <daniel@...rotopia.org>
Cc: Sky Huang <skylake.huang@...iatek.com>, netdev@...r.kernel.org,
	Sean Wang <sean.wang@...iatek.com>,
	linux-mediatek@...ts.infradead.org, linux-kernel@...r.kernel.org,
	Andrew Lunn <andrew+netdev@...n.ch>,
	Eric Dumazet <edumazet@...gle.com>,
	Matthias Brugger <matthias.bgg@...il.com>,
	linux-arm-kernel@...ts.infradead.org,
	Bo-Cun Chen <bc-bocun.chen@...iatek.com>,
	Eric Woudstra <ericwouds@...il.com>, Elad Yifee <eladwf@...il.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	Lorenzo Bianconi <lorenzo@...nel.org>,
	"David S. Miller" <davem@...emloft.net>,
	AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>,
	Felix Fietkau <nbd@....name>
Subject: Re: [PATCH net/next 3/3] net: ethernet: mtk_eth_soc: use genpool
 allocator for SRAM

On Sun, Jun 29, 2025 at 03:25:25PM +0100, Daniel Golle wrote:
> On Sat, Jun 28, 2025 at 10:13:51AM +0200, Andrew Lunn wrote:
> > > +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;
> > 	}
> > }
> 
> I've implemented that idea and the diffstat grew quite a lot. Also,
> it didn't really make the code more readable (see below why).

O.K, thanks for trying. Please keep with the casts back and forth.

	Andrew