linux-kernel - Re: [net-next v4 3/3] net: ethernet: mtk_eth_soc: change code to skip first IRQ completely

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Message-ID: <20250618083556.GE2545@horms.kernel.org>
Date: Wed, 18 Jun 2025 09:35:56 +0100
From: Simon Horman <horms@...nel.org>
To: Frank Wunderlich <linux@...web.de>
Cc: Felix Fietkau <nbd@....name>, Sean Wang <sean.wang@...iatek.com>,
	Lorenzo Bianconi <lorenzo@...nel.org>,
	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>,
	Matthias Brugger <matthias.bgg@...il.com>,
	AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>,
	Frank Wunderlich <frank-w@...lic-files.de>, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	linux-mediatek@...ts.infradead.org,
	Daniel Golle <daniel@...rotopia.org>, arinc.unal@...nc9.com
Subject: Re: [net-next v4 3/3] net: ethernet: mtk_eth_soc: change code to
 skip first IRQ completely

On Mon, Jun 16, 2025 at 10:07:36AM +0200, Frank Wunderlich wrote:
> From: Frank Wunderlich <frank-w@...lic-files.de>
> 
> On SoCs without MTK_SHARED_INT capability (mt7621 + mt7628) the first
> IRQ (eth->irq[0]) was read but never used. Do not read it and reduce
> the IRQ-count to 2 because of skipped index 0.

Describing the first IRQ as read seems a bit confusing to me - do we read
it? And saying get or got seems hard to parse. So perhaps something like
this would be clearer?

... platform_get_irq() is called for the first IRQ (eth->irq[0]) but
it is never used.

> 
> Signed-off-by: Frank Wunderlich <frank-w@...lic-files.de>
> ---
> v4:
> - drop >2 condition as max is already 2 and drop the else continue
> - update comment to explain which IRQs are taken in legacy way
> ---
>  drivers/net/ethernet/mediatek/mtk_eth_soc.c | 20 ++++++++++++++++----
>  drivers/net/ethernet/mediatek/mtk_eth_soc.h |  4 ++--
>  2 files changed, 18 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/net/ethernet/mediatek/mtk_eth_soc.c b/drivers/net/ethernet/mediatek/mtk_eth_soc.c
> index 3ecb399dcf81..f3fcbb00822c 100644
> --- a/drivers/net/ethernet/mediatek/mtk_eth_soc.c
> +++ b/drivers/net/ethernet/mediatek/mtk_eth_soc.c
> @@ -3341,16 +3341,28 @@ static int mtk_get_irqs(struct platform_device *pdev, struct mtk_eth *eth)
>  {
>  	int i;
>  
> +	/* future SoCs beginning with MT7988 should use named IRQs in dts */

Perhaps this comment belongs in the patch that adds support for named IRQs.

>  	eth->irq[MTK_ETH_IRQ_TX] = platform_get_irq_byname(pdev, "tx");
>  	eth->irq[MTK_ETH_IRQ_RX] = platform_get_irq_byname(pdev, "rx");
>  	if (eth->irq[MTK_ETH_IRQ_TX] >= 0 && eth->irq[MTK_ETH_IRQ_RX] >= 0)
>  		return 0;
>  
> +	/* legacy way:
> +	 * On MTK_SHARED_INT SoCs (MT7621 + MT7628) the first IRQ is taken from
> +	 * devicetree and used for rx+tx.
> +	 * On SoCs with non-shared IRQ the first was not used, second entry is
> +	 * TX and third is RX.

Maybe I am slow. But I had a bit of trouble parsing this.
Perhaps this is clearer?

        * devicetree and used for both RX and TX - it is shared.
	* On SoCs with non-shared IRQs the first entry is not used,
        * the second is for TX, and the third is for RX.

> +	 */
> +
>  	for (i = 0; i < MTK_ETH_IRQ_MAX; i++) {
> -		if (MTK_HAS_CAPS(eth->soc->caps, MTK_SHARED_INT) && i > 0)
> -			eth->irq[i] = eth->irq[MTK_ETH_IRQ_SHARED];
> -		else
> -			eth->irq[i] = platform_get_irq(pdev, i);
> +		if (MTK_HAS_CAPS(eth->soc->caps, MTK_SHARED_INT)) {
> +			if (i == 0)
> +				eth->irq[MTK_ETH_IRQ_SHARED] = platform_get_irq(pdev, i);
> +			else
> +				eth->irq[i] = eth->irq[MTK_ETH_IRQ_SHARED];
> +		} else {
> +			eth->irq[i] = platform_get_irq(pdev, i + 1);
> +		}
>  
>  		if (eth->irq[i] < 0) {
>  			dev_err(&pdev->dev, "no IRQ%d resource found\n", i);

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