linux-kernel - Re: [PATCH net v4 3/3] net: stmmac: Specify hardware capability value when FIFO size isn't specified

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Message-ID: <a4e31542-3534-4856-a90f-e47960ed0907@lunn.ch>
Date: Fri, 31 Jan 2025 15:47:45 +0100
From: Andrew Lunn <andrew@...n.ch>
To: Steven Price <steven.price@....com>
Cc: Kunihiko Hayashi <hayashi.kunihiko@...ionext.com>,
	Alexandre Torgue <alexandre.torgue@...s.st.com>,
	Jose Abreu <joabreu@...opsys.com>,
	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>,
	Maxime Coquelin <mcoquelin.stm32@...il.com>,
	Russell King <linux@...linux.org.uk>,
	Yanteng Si <si.yanteng@...ux.dev>, Furong Xu <0x1207@...il.com>,
	Joao Pinto <Joao.Pinto@...opsys.com>, netdev@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH net v4 3/3] net: stmmac: Specify hardware capability
 value when FIFO size isn't specified

> > I'm guessing, but in your setup, i assume the value is never written
> > to a register, hence 0 is O.K. e.g. dwmac1000_dma_operation_mode_rx(),
> > the fifosz value is used to determine if flow control can be used, but
> > is otherwise ignored.
> 
> I haven't traced the code, but that fits my assumptions too.

I could probably figure it out using code review, but do you know
which set of DMA operations your hardware uses? A quick look at
dwmac-rk.c i see:

        /* If the stmmac is not already selected as gmac4,
         * then make sure we fallback to gmac.
         */
        if (!plat_dat->has_gmac4)
                plat_dat->has_gmac = true;

Which suggests there are two variants of the RockChip MAC.

	Andrew