netdev - Re: [PATCH] net: mdio: mdio-bcm-unimac: Delay before first poll

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Message-ID: <ZXnHNTreKY/F2Aqm@shell.armlinux.org.uk>
Date: Wed, 13 Dec 2023 15:01:09 +0000
From: "Russell King (Oracle)" <linux@...linux.org.uk>
To: Andrew Lunn <andrew@...n.ch>
Cc: Justin Chen <justin.chen@...adcom.com>, netdev@...r.kernel.org,
	Doug Berger <opendmb@...il.com>,
	Florian Fainelli <florian.fainelli@...adcom.com>,
	Broadcom internal kernel review list <bcm-kernel-feedback-list@...adcom.com>,
	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>,
	open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] net: mdio: mdio-bcm-unimac: Delay before first poll

On Wed, Dec 13, 2023 at 11:57:52AM +0100, Andrew Lunn wrote:
> On Tue, Dec 12, 2023 at 04:02:49PM -0800, Justin Chen wrote:
> > With a clock interval of 400 nsec and a 64 bit transactions (32 bit
> > preamble & 16 bit control & 16 bit data), it is reasonable to assume
> > the mdio transaction will take 25.6 usec. Add a 30 usec delay before
> > the first poll to reduce the chance of a 1000-2000 usec sleep.
> 
> #define  MDIO_C45               0
> 
> suggests the hardware can do C45? The timing works out different then.
> Maybe add a comment by the udelay() that is assumes C22, to give a
> clue to somebody who is adding C45 support the delay needs to be
> re-evaluated.

Note, however, that the driver only supports C22 operations (it only
populates the read|write functions, not the c45 variants).

However, it doesn't explicitly set the MDIO_C22 bit in the configuration
register, so what ends up being spat out on the bus would be dependent
on the boot loader configuration.

However, I'm wondering why unimac_mdio_poll() isn't written as
(based on current code):

	return read_poll_timeout(unimac_mdio_readl(priv, MDIO_CMD), val,
				 !(val & MDIO_START_BUSY), 2000,
				 2000000);

rather than open-coding the io polling.

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