linux-kernel - Re: [net-next PATCH v5 9/9] net: phy: qca807x: add support for configurable LED

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Date: Fri, 2 Feb 2024 18:07:58 +0100
From: Christian Marangi <ansuelsmth@...il.com>
To: "Russell King (Oracle)" <linux@...linux.org.uk>
Cc: Andrew Lunn <andrew@...n.ch>, "David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	Rob Herring <robh+dt@...nel.org>,
	Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
	Conor Dooley <conor+dt@...nel.org>,
	Bjorn Andersson <andersson@...nel.org>,
	Konrad Dybcio <konrad.dybcio@...aro.org>,
	Heiner Kallweit <hkallweit1@...il.com>,
	Frank Rowand <frowand.list@...il.com>,
	Robert Marko <robert.marko@...tura.hr>, netdev@...r.kernel.org,
	devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-arm-msm@...r.kernel.org
Subject: Re: [net-next PATCH v5 9/9] net: phy: qca807x: add support for
 configurable LED

On Fri, Feb 02, 2024 at 05:04:23PM +0000, Russell King (Oracle) wrote:
> On Fri, Feb 02, 2024 at 05:40:21PM +0100, Christian Marangi wrote:
> > On Fri, Feb 02, 2024 at 02:43:37AM +0100, Andrew Lunn wrote:
> > > > +
> > > > +			phydev->drv->led_brightness_set = NULL;
> > > > +			phydev->drv->led_blink_set = NULL;
> > > > +			phydev->drv->led_hw_is_supported = NULL;
> > > > +			phydev->drv->led_hw_control_set = NULL;
> > > > +			phydev->drv->led_hw_control_get = NULL;
> > > 
> > > I don't see how that works. You have multiple PHYs using this
> > > driver. Some might have LEDs, some might have GPOs. But if you modify
> > > the driver structure like this, you prevent all PHYs from having LEDs,
> > > and maybe cause a Opps if a PHY device has already registered its
> > > LEDs?
> > >
> > 
> > God you are right! Off-topic but given the effects this may cause, why
> > the thing is not const? I assume it wouldn't make sense to add OPS based
> > on the detected feature since it would have side effect on other PHYs
> > that use the same driver.
> 
> Maybe phydev->drv should be const to avoid this kind of thing. It
> doesn't look like it would be hard to do, and importantly doesn't
> require casting away the const-ness anywhere. PHY drivers themselves
> can't be const because the driver model needs to be able to modify
> the embedded device_driver struct (e.g. see bus_add_driver().)
> 
>  drivers/net/phy/phy.c               | 3 +--
>  drivers/net/phy/phy_device.c        | 4 ++--
>  drivers/net/phy/xilinx_gmii2rgmii.c | 2 +-
>  include/linux/phy.h                 | 2 +-
>  4 files changed, 5 insertions(+), 6 deletions(-)
> 
> Just build-testing it.
>

Seems sensible to me. Also for everyone that does that (downstream or
driver that needs to be handled) it would result in a warning for
modifying const stuff. Maybe I'm wrong but I can only see benefits in
doing this change.

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