linux-kernel - Re: [PATCH RFC net-next v2 05/18] net: pse-pd: Add support for PSE device index

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Message-ID: <46d4b5be-60d3-4949-8eb9-9e8a036cb580@lunn.ch>
Date: Thu, 31 Oct 2024 22:28:29 +0100
From: Andrew Lunn <andrew@...n.ch>
To: Oleksij Rempel <o.rempel@...gutronix.de>
Cc: Kory Maincent <kory.maincent@...tlin.com>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	Jonathan Corbet <corbet@....net>,
	Donald Hunter <donald.hunter@...il.com>,
	Rob Herring <robh@...nel.org>, Andrew Lunn <andrew+netdev@...n.ch>,
	Simon Horman <horms@...nel.org>,
	Heiner Kallweit <hkallweit1@...il.com>,
	Russell King <linux@...linux.org.uk>,
	Liam Girdwood <lgirdwood@...il.com>,
	Mark Brown <broonie@...nel.org>,
	Thomas Petazzoni <thomas.petazzoni@...tlin.com>,
	linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
	linux-doc@...r.kernel.org, Kyle Swenson <kyle.swenson@....tech>,
	Dent Project <dentproject@...uxfoundation.org>,
	kernel@...gutronix.de,
	Maxime Chevallier <maxime.chevallier@...tlin.com>
Subject: Re: [PATCH RFC net-next v2 05/18] net: pse-pd: Add support for PSE
 device index

On Thu, Oct 31, 2024 at 07:27:59AM +0100, Oleksij Rempel wrote:
> On Wed, Oct 30, 2024 at 05:53:07PM +0100, Kory Maincent wrote:
> 
> ...
> >  /**
> >   * struct pse_control - a PSE control
> > @@ -440,18 +441,22 @@ int pse_controller_register(struct pse_controller_dev *pcdev)
> >  
> >  	mutex_init(&pcdev->lock);
> >  	INIT_LIST_HEAD(&pcdev->pse_control_head);
> > +	ret = ida_alloc_max(&pse_ida, INT_MAX, GFP_KERNEL);
> 
> s/INT_MAX/U32_MAX

 * Return: The allocated ID, or %-ENOMEM if memory could not be allocated,
 * or %-ENOSPC if there are no free IDs.

static inline int ida_alloc_max(struct ida *ida, unsigned int max, gfp_t gfp)

We need to be careful here, at least theoretically. Assuming a 32 bit
system, and you pass it U32_MAX, how does it return values in the
range S32_MAX..U32_MAX when it also needs to be able to return
negative numbers as errors?

I think the correct value to pass is S32_MAX, because it will always
fit in a u32, and there is space left for negative values for errors.

But this is probably theoretical, no real system should have that many
controllers.

	Andrew