linux-kernel - Re: [PATCH net 1/2] net: stmmac: Limit FIFO size by hardware feature value

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Message-ID: <636bad71-8da8-4fda-a433-1586d93683a5@lunn.ch>
Date: Thu, 16 Jan 2025 21:16:08 +0100
From: Andrew Lunn <andrew@...n.ch>
To: Kunihiko Hayashi <hayashi.kunihiko@...ionext.com>
Cc: 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>, netdev@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH net 1/2] net: stmmac: Limit FIFO size by hardware feature
 value

On Thu, Jan 16, 2025 at 11:08:52AM +0900, Kunihiko Hayashi wrote:
> Tx/Rx FIFO size is specified by the parameter "{tx,rx}-fifo-depth" from
> the platform layer.
> 
> However, these values are constrained by upper limits determined by the
> capabilities of each hardware feature. There is a risk that the upper
> bits will be truncated due to the calculation, so it's appropriate to
> limit them to the upper limit values.

Are these values hard coded in the platform layer? Or can they come
from userspace?

If they are hard coded, we should also fix them. So maybe add a
netdev_warn(), and encourage the platform maintainers to fix their
platform. If they are coming from userspace, we should consider
failing the ethtool call with an -EINVAL, and maybe an extack with the
valid range?

	Andrew