netdev - Re: [PATCH] Use a spinlock to guard `fep->ptp_clk

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Message-ID: <Yw9n/JfdenzRkAyq@hoboy.vegasvil.org>
Date:   Wed, 31 Aug 2022 06:54:04 -0700
From:   Richard Cochran <richardcochran@...il.com>
To:     Csókás Bence <csokas.bence@...lan.hu>
Cc:     netdev@...r.kernel.org, "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>, Andrew Lunn <andrew@...n.ch>,
        kernel@...gutronix.de, Marc Kleine-Budde <mkl@...gutronix.de>
Subject: Re: [PATCH] Use a spinlock to guard `fep->ptp_clk_on`

On Wed, Aug 31, 2022 at 02:56:31PM +0200, Csókás Bence wrote:

> diff --git a/drivers/net/ethernet/freescale/fec_ptp.c b/drivers/net/ethernet/freescale/fec_ptp.c
> index c74d04f4b2fd..dc8564a1f2d2 100644
> --- a/drivers/net/ethernet/freescale/fec_ptp.c
> +++ b/drivers/net/ethernet/freescale/fec_ptp.c
> @@ -365,21 +365,21 @@ static int fec_ptp_adjtime(struct ptp_clock_info *ptp, s64 delta)
>   */
>  static int fec_ptp_gettime(struct ptp_clock_info *ptp, struct timespec64 *ts)
>  {
> -	struct fec_enet_private *adapter =
> +	struct fec_enet_private *fep =
>  	    container_of(ptp, struct fec_enet_private, ptp_caps);
>  	u64 ns;
> -	unsigned long flags;
> +	unsigned long flags, flags2;
>  
> -	mutex_lock(&adapter->ptp_clk_mutex);
> +	spin_lock_irqsave(&fep->ptp_clk_lock, flags);
>  	/* Check the ptp clock */
> -	if (!adapter->ptp_clk_on) {
> -		mutex_unlock(&adapter->ptp_clk_mutex);
> +	if (!fep->ptp_clk_on) {

BTW This test is silly. If functionality isn't available then the code
should simply not register the clock in the first place.

> +		spin_unlock_irqrestore(&fep->ptp_clk_lock, flags);
>  		return -EINVAL;
>  	}
> -	spin_lock_irqsave(&adapter->tmreg_lock, flags);
> -	ns = timecounter_read(&adapter->tc);
> -	spin_unlock_irqrestore(&adapter->tmreg_lock, flags);
> -	mutex_unlock(&adapter->ptp_clk_mutex);
> +	spin_lock_irqsave(&fep->tmreg_lock, flags2);
> +	ns = timecounter_read(&fep->tc);
> +	spin_unlock_irqrestore(&fep->tmreg_lock, flags2);
> +	spin_unlock_irqrestore(&fep->ptp_clk_lock, flags);

Two spin locks?  Why not just use one?

Thanks,
Richard