linux-kernel - Re: [PATCH net v2 0/3] Limit devicetree parameters to hardware capability

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Message-ID: <c634eb72-6714-47e8-9270-b4ae99df9edf@socionext.com>
Date: Fri, 24 Jan 2025 13:19:53 +0900
From: Kunihiko Hayashi <hayashi.kunihiko@...ionext.com>
To: "Russell King (Oracle)" <linux@...linux.org.uk>
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>, 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 v2 0/3] Limit devicetree parameters to hardware
 capability

Hi Russell,

On 2025/01/24 1:31, Russell King (Oracle) wrote:
> On Thu, Jan 23, 2025 at 02:25:15PM +0900, Kunihiko Hayashi wrote:
>> Hi Russell,
>>
>> Thank you for your comment.
>>
>> On 2025/01/21 19:25, Russell King (Oracle) wrote:
>>> On Tue, Jan 21, 2025 at 01:41:35PM +0900, Kunihiko Hayashi wrote:
>>>> This series includes patches that checks the devicetree properties,
>>>> the number of MTL queues and FIFO size values, and if these
> specified
>>>> values exceed the value contained in the hardware capabilities,
> limit to
>>>> the values from the capabilities.
>>>>
>>>> And this sets hardware capability values if FIFO sizes are not
> specified
>>>> and removes redundant lines.
>>>
>>> I think you also indeed to explain why (and possibly understand) - if
>>> there are hardware capabilities that describe these parameters - it
> has
>>> been necessary to have them in firmware as well.
>>>
>>> There are two scenarios I can think of why these would be duplicated:
>>>
>>> 1. firmware/platform capabilities are there to correct wrong values
>>>      provided by the hardware.
>>> 2. firmware/platform capabilities are there to reduce the parameters
>>>      below hardware maximums.
>>>
>>> Which it is affects whether your patch is correct or not, and thus
> needs
>>> to be mentioned.
>>
>> I think scenario 2 applies in this case.
> 
> In light of my other reply
> (https://lore.kernel.org/r/Z4_ZilVFKacuAUE8@shell.armlinux.org.uk) I
> don't think either of my two above applies, and the driver is designed
> to allow platform code to override the hardware value, or to provide
> the value if there is no hardware value.

I understand. Especially I realized that I had to care about some hardwares
not having these values.

> My suggestion, therefore, would be (e.g.):
> 
> 	if (priv->dma_cap.rx_fifo_size &&
> 	    priv->plat->rx_fifo_size > priv->dma_cap.rx_fifo_size) {
> 		dev_warn(priv->device,
> 			 "Rx FIFO size exceeds dma capability (%d)\n",
> 			 priv->plat->rx_fifo_size);
> 		priv->plat->rx_fifo_size = priv->dma_cap.rx_fifo_size;
> 	}
> 
> if we still want to limit it to the hardware provided capability, where
> that is provided.

Thank you for your suggestion. I also came up with the same code in:
https://lore.kernel.org/all/c2aa354d-1bd5-4fb0-aa8b8-48fcce3c1628@socionext.com/#t

I'll reflect this code to the next.

Thank you,

---
Best Regards
Kunihiko Hayashi