Subject: Re: [PATCH 13/14] drivers: net: dsa: qca8k: protect MASTER busy_wait with mdio mutex

From: Andrew Lunn <[email-masked]>
Date: Fri, 23 Apr 2021 14:53:13 +0200

On Fri, Apr 23, 2021 at 03:47:39AM +0200, Ansuel Smith wrote:
> MDIO_MASTER operation have a dedicated busy wait that is not protected
> by the mdio mutex. This can cause situation where the MASTER operation
> is done and a normal operation is executed between the MASTER read/write
> and the MASTER busy_wait. Rework the qca8k_mdio_read/write function to
> address this issue by binding the lock for the whole MASTER operation
> and not only the mdio read/write common operation.
> 
> Signed-off-by: Ansuel Smith <[email-masked]>
> ---
>  drivers/net/dsa/qca8k.c | 59 ++++++++++++++++++++++++++++++++++-------
>  1 file changed, 50 insertions(+), 9 deletions(-)
> 
> diff --git a/drivers/net/dsa/qca8k.c b/drivers/net/dsa/qca8k.c
> index 88a0234f1a7b..d2f5e0b1c721 100644
> --- a/drivers/net/dsa/qca8k.c
> +++ b/drivers/net/dsa/qca8k.c
> @@ -609,9 +609,33 @@ qca8k_port_to_phy(int port)
>  	return port - 1;
>  }
>  
> +static int
> +qca8k_mdio_busy_wait(struct qca8k_priv *priv, u32 reg, u32 mask)
> +{
> +	unsigned long timeout;
> +	u16 r1, r2, page;
> +
> +	qca8k_split_addr(reg, &r1, &r2, &page);
> +
> +	timeout = jiffies + msecs_to_jiffies(20);
> +
> +	/* loop until the busy flag has cleared */
> +	do {
> +		u32 val = qca8k_mii_read32(priv->bus, 0x10 | r2, r1);
> +		int busy = val & mask;
> +
> +		if (!busy)
> +			break;
> +		cond_resched();
> +	} while (!time_after_eq(jiffies, timeout));
> +
> +	return time_after_eq(jiffies, timeout);

You should really be returning -ETIMEDOUT here on error.

    Andrew