netdev - Re: [PATCH v1 net-next] net: stmmac: Add support for MDIO interrupts

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Date:   Mon, 26 Aug 2019 15:31:46 -0700
From:   Florian Fainelli <f.fainelli@...il.com>
To:     Andrew Lunn <andrew@...n.ch>, Voon Weifeng <weifeng.voon@...el.com>
Cc:     "David S. Miller" <davem@...emloft.net>,
        Maxime Coquelin <mcoquelin.stm32@...il.com>,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        Jose Abreu <joabreu@...opsys.com>,
        Giuseppe Cavallaro <peppe.cavallaro@...com>,
        Alexandre Torgue <alexandre.torgue@...com>,
        Ong Boon Leong <boon.leong.ong@...el.com>
Subject: Re: [PATCH v1 net-next] net: stmmac: Add support for MDIO interrupts

On 8/26/19 11:47 AM, Andrew Lunn wrote:
> On Tue, Aug 27, 2019 at 09:45:20AM +0800, Voon Weifeng wrote:
>> From: "Chuah, Kim Tatt" <kim.tatt.chuah@...el.com>
>>
>> DW EQoS v5.xx controllers added capability for interrupt generation
>> when MDIO interface is done (GMII Busy bit is cleared).
>> This patch adds support for this interrupt on supported HW to avoid
>> polling on GMII Busy bit.
>>
>> stmmac_mdio_read() & stmmac_mdio_write() will sleep until wake_up() is
>> called by the interrupt handler.
> 
> Hi Voon
> 
> I _think_ there are some order of operation issues here. The mdiobus
> is registered in the probe function. As soon as of_mdiobus_register()
> is called, the MDIO bus must work. At that point MDIO read/writes can
> start to happen.
> 
> As far as i can see, the interrupt handler is only requested in
> stmmac_open(). So it seems like any MDIO operations after probe, but
> before open are going to fail?

AFAIR, wait_event_timeout() will continue to busy loop and wait until
the timeout, but not return an error because the polled condition was
true, at least that is my recollection from having the same issue with
the bcmgenet driver before it was moved to connecting to the PHY in the
ndo_open() function.
-- 
Florian