netdev - Re: [PATCH] net: phy: broadcom: Wire suspend/resume for BCM54612E

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Message-ID: <4890615.31r3eYUQgx@5cd116mnfx>
Date: Fri, 03 Nov 2023 02:47:38 +0100
From: Marco von Rosenberg <marcovr@...fnet.de>
To: Andrew Lunn <andrew@...n.ch>
Cc: Florian Fainelli <florian.fainelli@...adcom.com>,
 Broadcom internal kernel review list <bcm-kernel-feedback-list@...adcom.com>,
 Heiner Kallweit <hkallweit1@...il.com>, Russell King <linux@...linux.org.uk>,
 "David S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>,
 Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
 netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
 Marco von Rosenberg <marcovr@...fnet.de>
Subject: Re: [PATCH] net: phy: broadcom: Wire suspend/resume for BCM54612E

On Wednesday, November 1, 2023 11:06:56 PM CET Andrew Lunn wrote:
> On Wed, Nov 01, 2023 at 10:42:52PM +0100, Marco von Rosenberg wrote:
> > On Tuesday, October 31, 2023 1:31:11 AM CET Andrew Lunn wrote:
> > > Are we talking about a device which as been suspended? The PHY has
> > > been left running because there is no suspend callback? Something then
> > > triggers a resume. The bootloader then suspends the active PHY? Linux
> > > then boots, detects its a resume, so does not touch the hardware
> > > because there is no resume callback? The suspended PHY is then
> > > useless.
> > 
> > Hi Andrew,
> > 
> > thanks for your feedback. I guess a bit of context is missing here. The
> > issue has nothing to do with an ordinary suspension of the OS. The main
> > point is that on initial power-up, the bootloader suspends the PHY before
> > booting Linux. With a resume callback defined, Linux would call it on
> > boot and make the PHY usable.
> 
> Ah, so you rely on phy_attach_direct() calling phy_resume(phydev).
> 
> This seems an odd way to solve the problem. It was not Linux which
> suspend the PHY, so using resume is asymmetric.
> 
> I think soft_reset() or config_init() should be taking the PHY out of
> suspend.

I agree with all of your points. This is just one way which happens to solve
this specific problem. Of course it might be asymmetric to see the patch as
a solution to my problem. However is there anything fundamentally wrong with
adding suspend/resume callbacks? I see some other drivers having these
callbacks defined and some not (it seems a bit inconsistent throughout the
drivers in broadcom.c to be honest).

I'm wondering if I should just omit this whole "motivation" paragraph in the 
commit message and just use the commit message of commit 38b6a9073007 ("net: 
phy: broadcom: Wire suspend/resume for BCM50610 and BCM50610M") as a template.
I mean, regardless of my motivation, I would say it makes sense for this PHY 
to support suspend and resume.

	Marco