linux-kernel - Re: [PATCH net-next] net: ethernet: mediatek: ppe: fix busy wait loop

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Message-ID: <YHjH3DxteZrID2hW@lunn.ch>
Date:   Fri, 16 Apr 2021 01:10:20 +0200
From:   Andrew Lunn <andrew@...n.ch>
To:     Ilya Lipnitskiy <ilya.lipnitskiy@...il.com>
Cc:     Felix Fietkau <nbd@....name>, John Crispin <john@...ozen.org>,
        Sean Wang <sean.wang@...iatek.com>,
        Mark Lee <Mark-MC.Lee@...iatek.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Matthias Brugger <matthias.bgg@...il.com>,
        Pablo Neira Ayuso <pablo@...filter.org>,
        netdev@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-mediatek@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH net-next] net: ethernet: mediatek: ppe: fix busy wait loop

On Thu, Apr 15, 2021 at 04:02:34PM -0700, Ilya Lipnitskiy wrote:
> The intention is for the loop to timeout if the body does not succeed.
> The current logic calls time_is_before_jiffies(timeout) which is false
> until after the timeout, so the loop body never executes.
> 
> time_is_after_jiffies(timeout) will return true until timeout is less
> than jiffies, which is the intended behavior here.
> 
> Fixes: ba37b7caf1ed ("net: ethernet: mtk_eth_soc: add support for initializing the PPE")
> Signed-off-by: Ilya Lipnitskiy <ilya.lipnitskiy@...il.com>
> Cc: Felix Fietkau <nbd@....name>
> ---
>  drivers/net/ethernet/mediatek/mtk_ppe.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/net/ethernet/mediatek/mtk_ppe.c b/drivers/net/ethernet/mediatek/mtk_ppe.c
> index 71e1ccea6e72..af3c266297aa 100644
> --- a/drivers/net/ethernet/mediatek/mtk_ppe.c
> +++ b/drivers/net/ethernet/mediatek/mtk_ppe.c
> @@ -46,7 +46,7 @@ static int mtk_ppe_wait_busy(struct mtk_ppe *ppe)
>  {
>  	unsigned long timeout = jiffies + HZ;
>  
> -	while (time_is_before_jiffies(timeout)) {
> +	while (time_is_after_jiffies(timeout)) {
>  		if (!(ppe_r32(ppe, MTK_PPE_GLO_CFG) & MTK_PPE_GLO_CFG_BUSY))
>  			return 0;

Maybe see is iopoll.h can be used.

      Andrew

>  
> -- 
> 2.31.1
> 
> 
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> linux-arm-kernel@...ts.infradead.org
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