netdev - Re: [net-next PATCH 2/2] net: phy: leds: use new define for link speed modes number

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Date: Wed, 13 Dec 2023 20:18:38 +0000
From: "Russell King (Oracle)" <linux@...linux.org.uk>
To: Christian Marangi <ansuelsmth@...il.com>
Cc: Andrew Lunn <andrew@...n.ch>, Heiner Kallweit <hkallweit1@...il.com>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	Vladimir Oltean <vladimir.oltean@....com>,
	Vincent Mailhol <mailhol.vincent@...adoo.fr>,
	Kees Cook <keescook@...omium.org>,
	Piergiorgio Beruto <piergiorgio.beruto@...il.com>,
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [net-next PATCH 2/2] net: phy: leds: use new define for link
 speed modes number

On Wed, Dec 13, 2023 at 07:15:54PM +0100, Christian Marangi wrote:
> Use new define __LINK_SPEEDS_NUM for the speeds array instead of
> declaring a big enough array of 50 elements to handle future link speed
> modes.
> 
> Signed-off-by: Christian Marangi <ansuelsmth@...il.com>
> ---
>  drivers/net/phy/phy_led_triggers.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/net/phy/phy_led_triggers.c b/drivers/net/phy/phy_led_triggers.c
> index f550576eb9da..40cb0fa9ace0 100644
> --- a/drivers/net/phy/phy_led_triggers.c
> +++ b/drivers/net/phy/phy_led_triggers.c
> @@ -84,7 +84,7 @@ static void phy_led_trigger_unregister(struct phy_led_trigger *plt)
>  int phy_led_triggers_register(struct phy_device *phy)
>  {
>  	int i, err;
> -	unsigned int speeds[50];
> +	unsigned int speeds[__LINK_SPEEDS_NUM];
>  
>  	phy->phy_num_led_triggers = phy_supported_speeds(phy, speeds,
>  							 ARRAY_SIZE(speeds));

Yes, I agree the original code is utterly horrid, and there should be a
definition for its size. However, this is about the only place it would
be used - if you look at the code in phy_supported_speeds() and in
phy_speeds() which it calls, there is nothing in there which would know
the speed.

The only two solution I can think would be either a new function:

size_t phy_num_supported_speeds(struct phy_device *phydev);

or have phy_speeds() return the number of entries if "speeds" was NULL.

Then kmalloc_array() the speed array - but that seems a bit on the
side of things. The code as it stands is safe, because the passed
ARRAY_SIZE() limits the maximum index into speeds[] that will be
written, and it will result in the slower speeds not being added
into the array.

-- 
RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
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