netdev - Re: [PATCH net-next v2 03/17] net: stmmac: use correct type for tx_lpi

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Message-ID: <20250107112851.GE33144@kernel.org>
Date: Tue, 7 Jan 2025 11:28:51 +0000
From: Simon Horman <horms@...nel.org>
To: "Russell King (Oracle)" <rmk+kernel@...linux.org.uk>
Cc: Andrew Lunn <andrew@...n.ch>, Heiner Kallweit <hkallweit1@...il.com>,
	Alexandre Torgue <alexandre.torgue@...s.st.com>,
	Andrew Lunn <andrew+netdev@...n.ch>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Jose Abreu <joabreu@...opsys.com>,
	linux-arm-kernel@...ts.infradead.org,
	linux-stm32@...md-mailman.stormreply.com,
	Maxime Coquelin <mcoquelin.stm32@...il.com>, netdev@...r.kernel.org,
	Paolo Abeni <pabeni@...hat.com>
Subject: Re: [PATCH net-next v2 03/17] net: stmmac: use correct type for
 tx_lpi_timer

On Mon, Jan 06, 2025 at 12:24:58PM +0000, Russell King (Oracle) wrote:
> The ethtool interface uses u32 for tx_lpi_timer, and so does phylib.
> Use u32 to store this internally within stmmac rather than "int"
> which could misinterpret large values.
> 
> Since eee_timer is used to initialise priv->tx_lpi_timer, this also
> should be unsigned to avoid a negative number being interpreted as a
> very large positive number.
> 
> Also correct "value" in dwmac4_set_eee_lpi_entry_timer() to use u32
> rather than int, which is derived from tx_lpi_timer, even though
> masking with STMMAC_ET_MAX will truncate the sign bits. u32 is the
> value argument type for writel().
> 
> Signed-off-by: Russell King (Oracle) <rmk+kernel@...linux.org.uk>

...

> diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
> index 9a9169ca7cd2..b0ef439b715b 100644
> --- a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
> +++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
> @@ -111,8 +111,8 @@ static const u32 default_msg_level = (NETIF_MSG_DRV | NETIF_MSG_PROBE |
>  				      NETIF_MSG_IFDOWN | NETIF_MSG_TIMER);
>  
>  #define STMMAC_DEFAULT_LPI_TIMER	1000
> -static int eee_timer = STMMAC_DEFAULT_LPI_TIMER;
> -module_param(eee_timer, int, 0644);
> +static unsigned int eee_timer = STMMAC_DEFAULT_LPI_TIMER;
> +module_param(eee_timer, uint, 0644);
>  MODULE_PARM_DESC(eee_timer, "LPI tx expiration time in msec");
>  #define STMMAC_LPI_T(x) (jiffies + usecs_to_jiffies(x))
>  

Hi Russell,

now that eee_timer is unsigned the following check in stmmac_verify_args()
can never be true. I guess it should be removed.

        if (eee_timer < 0)
                eee_timer = STMMAC_DEFAULT_LPI_TIMER;

Flagged by Smatch.

...