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

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Message-ID: <6aa0671d-beb2-429b-a34e-cb35651e1c12@socionext.com>
Date: Mon, 20 Jan 2025 14:20:23 +0900
From: Kunihiko Hayashi <hayashi.kunihiko@...ionext.com>
To: Andrew Lunn <andrew@...n.ch>
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

Hi Andrew,

On 2025/01/17 5:16, Andrew Lunn wrote:
> 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?

My explanation is insufficient and misleading.
"From the platform layer" means the common layer of stmmac described in
"stmmac_platform.c".

> 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?

These values are derived from the devicetree and stored in the stmmac
private structure. They are hardware-specific values, so I think this
fix is sufficient.

Thank you,

---
Best Regards
Kunihiko Hayashi