netdev - Re: [PATCH net v3 1/3] net: stmmac: Limit the number of MTL queues to hardware capability

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Message-ID: <Z5N8-2XVAFBn1BCY@shell.armlinux.org.uk>
Date: Fri, 24 Jan 2025 11:43:55 +0000
From: "Russell King (Oracle)" <linux@...linux.org.uk>
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>,
	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 v3 1/3] net: stmmac: Limit the number of MTL queues
 to hardware capability

On Fri, Jan 24, 2025 at 07:13:57PM +0900, Kunihiko Hayashi wrote:
> The number of MTL queues to use is specified by the parameter
> "snps,{tx,rx}-queues-to-use" from stmmac_platform layer.
> 
> However, the maximum numbers of queues are constrained by upper limits
> determined by the capability of each hardware feature. It's appropriate
> to limit the values not to exceed the upper limit values and display
> a warning message.
> 
> This only works if the hardware capability has the upper limit values.
> 
> Fixes: d976a525c371 ("net: stmmac: multiple queues dt configuration")
> Signed-off-by: Kunihiko Hayashi <hayashi.kunihiko@...ionext.com>
> ---
>  drivers/net/ethernet/stmicro/stmmac/stmmac_main.c | 15 +++++++++++++++
>  1 file changed, 15 insertions(+)
> 
> diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
> index 7bf275f127c9..be1e6fa6d557 100644
> --- a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
> +++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
> @@ -7232,6 +7232,21 @@ static int stmmac_hw_init(struct stmmac_priv *priv)
>  	if (priv->dma_cap.tsoen)
>  		dev_info(priv->device, "TSO supported\n");
>  
> +	if (priv->dma_cap.number_rx_queues &&
> +	    priv->dma_cap.number_rx_queues < priv->plat->rx_queues_to_use) {

While this looks "nicer", which of these two do you think reads better
and is easier to understand:

"If priv->dma_cap.number_rx_queues is set, and
 priv->dma_cap.number_rx_queues is less than
 priv->plat->rx_queues_to_use then print a message about
 priv->plat->rx_queues_to_use exceeding priv->dma_cap.number_rx_queues"

"If priv->dma_cap.number_rx_queues is set, and
 priv->plat->rx_queues_to_use is greater than
 priv->dma_cap.number_rx_queues, then print a message about
 priv->plat->rx_queues_to_use exceeding priv->dma_cap.number_rx_queues"

With the former one has to mentally flip the test around in the if
statement to check that it does indeed match the warning that is
printed.

-- 
RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
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