netdev - Re: [net-next RFC PATCH 1/6] net: phy: add support for defining multiple PHY IDs in PHY driver

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Message-ID: <ZdJpyGkFRiRufySw@shell.armlinux.org.uk>
Date: Sun, 18 Feb 2024 20:34:16 +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>,
	Florian Fainelli <florian.fainelli@...adcom.com>,
	Broadcom internal kernel review list <bcm-kernel-feedback-list@...adcom.com>,
	Robert Marko <robimarko@...il.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Pieter Jansen van Vuuren <pieter.jansen-van-vuuren@....com>,
	Nipun Gupta <nipun.gupta@....com>,
	Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
	Puneet Gupta <puneet.gupta@....com>,
	Abhijit Gangurde <abhijit.gangurde@....com>,
	Umang Jain <umang.jain@...asonboard.com>, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [net-next RFC PATCH 1/6] net: phy: add support for defining
 multiple PHY IDs in PHY driver

On Sun, Feb 18, 2024 at 09:27:22PM +0100, Christian Marangi wrote:
> On Sun, Feb 18, 2024 at 09:10:30PM +0100, Andrew Lunn wrote:
> > > > > +	phy_dev_id = (struct mdio_device_id *)&phydev->dev_id;
> > > > 
> > > > Why this cast? Try to write code that doesn't need casts.
> > > > 
> > > 
> > > This cast is needed to keep the dev_id const in the phy_device struct so
> > > that other are warned to not modify it and should only be handled by
> > > phy_probe since it's the one that fills it.
> > > 
> > > Alternative is to drop const and drop the warning.
> > 
> > Can you propagate the const. Make phy_dev_id point to a const?
> >
> 
> Mhh not following, I tried changing to const struct mdio_device_id *phy_dev_id
> but that results in memcpy complain (dest is void * not const) and
> writing in read-only for the single PHY part (the else part)
> 
> An alternative might be to make dev_id a pointer in struct phy_device
> and dynamically allocate a mdio_device_id for the case of single PHY
> (else case). That effectively remove the need of this cast but I would
> love to skip checking for -ENOMEM (this is why i made that local)
> 
> If it's OK to dynamically allocate for the else case then I will make
> this change. I just tested this implementation and works correctly with
> not warning.

Why do we need memcpy() etc - as I demonstrated in my proposal, it's
not necessary if we introduce a mdio_device_id within struct phy_driver
and we can just store a const pointer to the mdio_device_id that
matched. That was very much an intentional decision in my proposal to
make the code simple.

-- 
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