linux-kernel - Re: [PATCH] net: dsa: sja1105: fix speed setting for 10 MBPS

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Message-ID: <ccfa3bc1-cdbd-f990-321f-55555531d56d@cogentembedded.com>
Date:   Sat, 2 May 2020 15:21:20 +0300
From:   Sergei Shtylyov <sergei.shtylyov@...entembedded.com>
To:     Colin King <colin.king@...onical.com>,
        Vladimir Oltean <olteanv@...il.com>,
        Andrew Lunn <andrew@...n.ch>,
        Vivien Didelot <vivien.didelot@...il.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        "David S . Miller" <davem@...emloft.net>,
        Russell King <rmk+kernel@...linux.org.uk>,
        linux-kernel@...r.kernel.org
Cc:     kernel-janitors@...r.kernel.org, netdev@...r.kernel.org
Subject: Re: [PATCH] net: dsa: sja1105: fix speed setting for 10 MBPS

Hello!

On 01.05.2020 16:43, Colin King wrote:

> From: Colin Ian King <colin.king@...onical.com>
> 
> The current logic for speed checking will never set the speed to 10 MBPS
> because bmcr & BMCR_SPEED10 is always 0 since BMCR_SPEED10 is 0. Also
> the erroneous setting where BMCR_SPEED1000 and BMCR_SPEED100 are both
> set causes the speed to be 1000 MBS.  Fix this by masking bps and checking
> for just the expected settings of BMCR_SPEED1000, BMCR_SPEED100 and
> BMCR_SPEED10 and defaulting to the unknown speed otherwise.
> 
> Addresses-Coverity: ("Logically dead code")
> Fixes: ffe10e679cec ("net: dsa: sja1105: Add support for the SGMII port")
> Signed-off-by: Colin Ian King <colin.king@...onical.com>
> ---
>   drivers/net/dsa/sja1105/sja1105_main.c | 11 +++++++----
>   1 file changed, 7 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/net/dsa/sja1105/sja1105_main.c b/drivers/net/dsa/sja1105/sja1105_main.c
> index 472f4eb20c49..59a9038cdc4e 100644
> --- a/drivers/net/dsa/sja1105/sja1105_main.c
> +++ b/drivers/net/dsa/sja1105/sja1105_main.c
> @@ -1600,6 +1600,7 @@ static const char * const sja1105_reset_reasons[] = {
>   int sja1105_static_config_reload(struct sja1105_private *priv,
>   				 enum sja1105_reset_reason reason)
>   {
> +	const int mask = (BMCR_SPEED1000 | BMCR_SPEED100 | BMCR_SPEED10);

    Why not declare it in the block it's used in? Also, () not needed here.

>   	struct ptp_system_timestamp ptp_sts_before;
>   	struct ptp_system_timestamp ptp_sts_after;
>   	struct sja1105_mac_config_entry *mac;
> @@ -1684,14 +1685,16 @@ int sja1105_static_config_reload(struct sja1105_private *priv,
>   		sja1105_sgmii_pcs_config(priv, an_enabled, false);
>   
>   		if (!an_enabled) {
> -			int speed = SPEED_UNKNOWN;
> +			int speed;

    Why not the following?

		int mask = bmcr & (BMCR_SPEED1000 | BMCR_SPEED100 |
			   BMCR_SPEED10);			

>   
> -			if (bmcr & BMCR_SPEED1000)
> +			if ((bmcr & mask) == BMCR_SPEED1000)
>   				speed = SPEED_1000;
> -			else if (bmcr & BMCR_SPEED100)
> +			else if ((bmcr & mask) == BMCR_SPEED100)
>   				speed = SPEED_100;
> -			else if (bmcr & BMCR_SPEED10)
> +			else if ((bmcr & mask) == BMCR_SPEED10)
>   				speed = SPEED_10;
> +			else
> +				speed = SPEED_UNKNOWN;
>   
>   			sja1105_sgmii_pcs_force_speed(priv, speed);
>   		}

MBR, Sergei