Re: [PATCH 09/15] net: phy: delay PHY driver probe until PHY registration - Russell King

From: Russell King - ARM Linux admin <linux@armlinux.org.uk>
To: Florian Fainelli <f.fainelli@gmail.com>
Cc: Andrew Lunn <andrew@lunn.ch>,
	Alexandre Belloni <alexandre.belloni@bootlin.com>,
	devicetree <devicetree@vger.kernel.org>,
	Vladimir Oltean <vladimir.oltean@nxp.com>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	Fabien Parent <fparent@baylibre.com>,
	Iyappan Subramanian <iyappan@os.amperecomputing.com>,
	Quan Nguyen <quan@os.amperecomputing.com>,
	Frank Rowand <frowand.list@gmail.com>,
	Bartosz Golaszewski <brgl@bgdev.pl>,
	Bartosz Golaszewski <bgolaszewski@baylibre.com>,
	Jakub Kicinski <kuba@kernel.org>,
	Yisen Zhuang <yisen.zhuang@huawei.com>,
	Vivien Didelot <vivien.didelot@gmail.com>,
	Tom Lendacky <thomas.lendacky@amd.com>,
	Andrew Perepech <andrew.perepech@mediatek.com>,
	Stephane Le Provost <stephane.leprovost@mediatek.com>,
	Keyur Chudgar <keyur@os.amperecomputing.com>,
	Jassi Brar <jaswinder.singh@linaro.org>,
	Claudiu Manoil <claudiu.manoil@nxp.com>,
	Rob Herring <robh+dt@kernel.org>,
	"moderated list:ARM/Mediatek SoC..."
	<linux-mediatek@lists.infradead.org>,
	Matthias Brugger <matthias.bgg@gmail.com>,
	Linux ARM <linux-arm-kernel@lists.infradead.org>,
	Salil Mehta <salil.mehta@huawei.com>,
	netdev <netdev@vger.kernel.org>,
	Ilias Apalodimas <ilias.apalodimas@linaro.org>,
	Liam Girdwood <lgirdwood@gmail.com>,
	Microchip Linux Driver Support <UNGLinuxDriver@microchip.com>,
	Mark Brown <broonie@kernel.org>,
	Philipp Zabel <p.zabel@pengutronix.de>,
	Pedro Tsai <pedro.tsai@mediatek.com>,
	"David S . Miller" <davem@davemloft.net>,
	Heiner Kallweit <hkallweit1@gmail.com>
Subject: Re: [PATCH 09/15] net: phy: delay PHY driver probe until PHY registration
Date: Wed, 24 Jun 2020 17:50:16 +0100	[thread overview]
Message-ID: <20200624165016.GA1551@shell.armlinux.org.uk> (raw)
In-Reply-To: <f806586d-a6d7-99af-bba4-d1e7d28be192@gmail.com>

On Wed, Jun 24, 2020 at 09:06:28AM -0700, Florian Fainelli wrote:
> On 6/24/2020 6:48 AM, Bartosz Golaszewski wrote:
> > I didn't expect to open such a can of worms...
> > 
> > This has evolved into several new concepts being proposed vs my
> > use-case which is relatively simple. The former will probably take
> > several months of development, reviews and discussions and it will
> > block supporting the phy supply on pumpkin boards upstream. I would
> > prefer not to redo what other MAC drivers do (phy-supply property on
> > the MAC node, controlling it from the MAC driver itself) if we've
> > already established it's wrong.
> 
> You are not new to Linux development, so none of this should come as a
> surprise to you. Your proposed solution has clearly short comings and is
> a hack, especially around the PHY_ID_NONE business to get a phy_device
> only then to have the real PHY device ID. You should also now that "I
> need it now because my product deliverable depends on it" has never been
> received as a valid argument to coerce people into accepting a solution
> for which there are at review time known deficiencies to the proposed
> approach.

It /is/ a generic issue.  The same problem exists for AMBA Primecell
devices, and that code has an internal deferred device list that it
manages.  See drivers/amba/bus.c, amba_deferred_retry_func(),
amba_device_try_add(), and amba_device_add().

As we see more devices gain this property, it needs to be addressed
in a generic way, rather than coming up with multiple bus specific
implementations.

Maybe struct bus_type needs a method to do the preparation to add
a device (such as reading IDs etc), which is called by device_add().
If that method returns -EPROBE_DEFER, the device gets added to a
deferred list, which gets retried when drivers are successfully
probed.  Possible maybe?

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