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

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Message-ID: <Yw9qO+3WqqTUAsIG@lunn.ch>
Date:   Wed, 31 Aug 2022 16:03:39 +0200
From:   Andrew Lunn <andrew@...n.ch>
To:     Csókás Bence <csokas.bence@...lan.hu>
Cc:     netdev@...r.kernel.org, Richard Cochran <richardcochran@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>, 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:
> Mutexes cannot be taken in a non-preemptible context,
> causing a panic in `fec_ptp_save_state()`. Replacing
> `ptp_clk_mutex` by `ptp_clk_lock` fixes this.
> 
> Fixes: 91c0d987a9788dcc5fe26baafd73bf9242b68900
> Fixes: 6a4d7234ae9a3bb31181f348ade9bbdb55aeb5c5
> Fixes: f79959220fa5fbda939592bf91c7a9ea90419040
> 
> Reported-by: Marc Kleine-Budde <mkl@...gutronix.de>
> 
> Signed-off-by: Csókás Bence <csokas.bence@...lan.hu>
> ---
>  drivers/net/ethernet/freescale/fec.h      |  2 +-
>  drivers/net/ethernet/freescale/fec_main.c | 17 ++++++------
>  drivers/net/ethernet/freescale/fec_ptp.c  | 32 +++++++++++------------
>  3 files changed, 26 insertions(+), 25 deletions(-)
> 
> diff --git a/drivers/net/ethernet/freescale/fec.h b/drivers/net/ethernet/freescale/fec.h
> index 0cebe4b63adb..9aac74d14f26 100644
> --- a/drivers/net/ethernet/freescale/fec.h
> +++ b/drivers/net/ethernet/freescale/fec.h
> @@ -557,7 +557,7 @@ struct fec_enet_private {
>  	struct clk *clk_2x_txclk;
>  
>  	bool ptp_clk_on;
> -	struct mutex ptp_clk_mutex;
> +	spinlock_t ptp_clk_lock;
>  	unsigned int num_tx_queues;
>  	unsigned int num_rx_queues;
>  
> diff --git a/drivers/net/ethernet/freescale/fec_main.c b/drivers/net/ethernet/freescale/fec_main.c
> index b0d60f898249..98d8f8d6034e 100644
> --- a/drivers/net/ethernet/freescale/fec_main.c
> +++ b/drivers/net/ethernet/freescale/fec_main.c
> @@ -2029,6 +2029,7 @@ static int fec_enet_clk_enable(struct net_device *ndev, bool enable)
>  {
>  	struct fec_enet_private *fep = netdev_priv(ndev);
>  	int ret;
> +	unsigned long flags;

Please keep to reverse christmas tree
  
>  	if (enable) {
>  		ret = clk_prepare_enable(fep->clk_enet_out);
> @@ -2036,15 +2037,15 @@ static int fec_enet_clk_enable(struct net_device *ndev, bool enable)
>  			return ret;
>  
>  		if (fep->clk_ptp) {
> -			mutex_lock(&fep->ptp_clk_mutex);
> +			spin_lock_irqsave(&fep->ptp_clk_lock, flags);

Is the ptp hardware accessed in interrupt context? If not, you can use
a plain spinlock, not _irqsave..

Looking at fec_enet_interrupt() and fec_enet_collect_events() i do not
see anything.

    Andrew