linux-kernel - Re: [PATCH] net: stmmac: fix rx queue priority assignment

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Date: Mon, 19 Feb 2024 11:40:56 +0100 (CET)
From: Romain Gantois <romain.gantois@...tlin.com>
To: Piotr Wejman <piotrwejman90@...il.com>
cc: Alexandre Torgue <alexandre.torgue@...s.st.com>, 
    Jose Abreu <joabreu@...opsys.com>, "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-stm32@...md-mailman.stormreply.com, 
    linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] net: stmmac: fix rx queue priority assignment

Hello Piotr,

On Mon, 19 Feb 2024, Piotr Wejman wrote:

>  static void dwmac4_rx_queue_priority(struct mac_device_info *hw,
> -				     u32 prio, u32 queue)
> +				     u32 prio_mask, u32 queue)
>  {
>  	void __iomem *ioaddr = hw->pcsr;
> -	u32 base_register;
> -	u32 value;
> +	u32 clear_mask = 0;
> +	u32 ctrl2, ctrl3;
> +	int i;
>  
> -	base_register = (queue < 4) ? GMAC_RXQ_CTRL2 : GMAC_RXQ_CTRL3;
> -	if (queue >= 4)
> -		queue -= 4;
> +	ctrl2 = readl(ioaddr + GMAC_RXQ_CTRL2);
> +	ctrl3 = readl(ioaddr + GMAC_RXQ_CTRL3);
>  
> -	value = readl(ioaddr + base_register);
> +	for (i = 0; i < 4; i++)
> +		clear_mask |= ((prio_mask << GMAC_RXQCTRL_PSRQX_SHIFT(i)) &
> +						GMAC_RXQCTRL_PSRQX_MASK(i));
>  
> -	value &= ~GMAC_RXQCTRL_PSRQX_MASK(queue);
> -	value |= (prio << GMAC_RXQCTRL_PSRQX_SHIFT(queue)) &
> +	ctrl2 &= ~clear_mask;
> +	ctrl3 &= ~clear_mask;
> +
> +	if (queue < 4) {
> +		ctrl2 |= (prio_mask << GMAC_RXQCTRL_PSRQX_SHIFT(queue)) &
This is a bit of a nitpick but do you think it would make sense to replace that 
"4" with a macro? Something like GMAC_RXQCTRL_PSRXQ_MAXCTRL2QUEUE?

>  						GMAC_RXQCTRL_PSRQX_MASK(queue);
> -	writel(value, ioaddr + base_register);
> +
> +		writel(ctrl2, ioaddr + GMAC_RXQ_CTRL2);
> +		writel(ctrl3, ioaddr + GMAC_RXQ_CTRL3);
I suppose that the order of these two writes are somehow important, else these 
could be factored out of the conditional block. Could you maybe add a short 
comment that explains why the order of these writes matter?

Best Regards,

-- 
Romain Gantois, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com