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

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Message-ID: <8c2ecfb0-cfbc-439c-a0b5-b9e18a5eef98@roeck-us.net>
Date: Sat, 1 Feb 2025 14:02:15 -0800
From: Guenter Roeck <linux@...ck-us.net>
To: "Russell King (Oracle)" <linux@...linux.org.uk>
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>,
 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

On 2/1/25 12:35, Russell King (Oracle) wrote:
> On Sat, Feb 01, 2025 at 11:14:41AM -0800, Guenter Roeck wrote:
>> Hi,
>>
>> On Mon, Jan 27, 2025 at 10:38:20AM +0900, Kunihiko Hayashi wrote:
>>> When Tx/Rx FIFO size is not specified in advance, the driver checks if
>>> the value is zero and sets the hardware capability value in functions
>>> where that value is used.
>>>
>>> Consolidate the check and settings into function stmmac_hw_init() and
>>> remove redundant other statements.
>>>
>>> If FIFO size is zero and the hardware capability also doesn't have upper
>>> limit values, return with an error message.
>>>
>>> Signed-off-by: Kunihiko Hayashi <hayashi.kunihiko@...ionext.com>
>>
>> This patch breaks qemu's stmmac emulation, for example for
>> npcm750-evb. The error message is:
>> 	stmmaceth f0804000.eth: Can't specify Rx FIFO size
> 
> Interesting. I looked at QEMU to see whether anything in the Debian
> stable version of QEMU might possibly have STMMAC emulation, but
> drew a blank... Even trying to find where in QEMU it emulates the
> STMMAC. I do see that it does include this, so maybe I can use that
> to test some of my stmmac changes. Thanks!
> 

Support was added in qemu v9.0.0. See qemu commit 08f787a34c
("hw/net: Add NPCMXXX GMAC device"). It doesn't directly say what
the emulated hardware actually is, but the commit message says

     The following message shows up with the change:
     Broadcom BCM54612E stmmac-0:00: attached PHY driver [Broadcom BCM54612E] (mii_bus:phy_addr=stmmac-0:00, irq=POLL)
     stmmaceth f0802000.eth eth0: Link is Up - 1Gbps/Full - flow control rx/tx

so that is a bit of a hint.

Guenter