Re: [PATCH v2 1/4] net: macb: Check MDIO state before read/write and use timeouts

From: Harini Katakam <harinik@xilinx.com>
To: Andrew Lunn <andrew@lunn.ch>
Cc: Claudiu Beznea <Claudiu.Beznea@microchip.com>,
	Harini Katakam <harini.katakam@xilinx.com>,
	Nicolas Ferre <Nicolas.Ferre@microchip.com>,
	David Miller <davem@davemloft.net>,
	netdev@vger.kernel.org, linux-kernel@vger.kernel.org,
	Michal Simek <michal.simek@xilinx.com>,
	Shubhrajyoti Datta <shubhrajyoti.datta@xilinx.com>,
	sai.pavan.boddu@xilinx.com
Subject: Re: [PATCH v2 1/4] net: macb: Check MDIO state before read/write and use timeouts
Date: Tue, 27 Nov 2018 11:06:36 +0530	[thread overview]
Message-ID: <CAFcVECK=4e-+1u3X+OuLoAEicUtrkTX3C0wzAugMRcJSP0N-Vg@mail.gmail.com> (raw)
In-Reply-To: <20181126145210.GD12116@lunn.ch>

Hi Claudiu,
On Mon, Nov 26, 2018 at 8:22 PM Andrew Lunn <andrew@lunn.ch> wrote:
>
> On Mon, Nov 26, 2018 at 02:46:01PM +0000, Claudiu.Beznea@microchip.com wrote:
> > Hi Harini,
> >
> > On 26.11.2018 09:07, Harini Katakam wrote:
> > > From: Harini Katakam <harinik@xilinx.com>
> > >
> > > Replace the while loop in MDIO read/write functions with a timeout.
> > > In addition, add a check for MDIO bus busy before initiating a new
> > > operation as well to make sure there is no ongoing MDIO operation.
> >
> > Is this MDIO bus busy check necessary? The caller of
> > macb_mdio_read/macb_mdio_write locks the mdio bus mutex before calling it
> > (e.g. mdiobus_read).
>
> Hi Claudiu
>
> It depends on the implementation. A write operation you could just
> launch, but not wait for it to complete, allowing you to do other
> stuff while the hardware is busy. For the next operation you then do
> need to check the previous operation has completed.
>
> I've not checked it is actually implemented this way.

Yes, as Andrew mentioned, a previous MDIO bus operation cannot
be assumed to be complete always - for ex., in case of a timeout.
There is a chance that the MDIO bus bit is busy when mdio_read/write
is called.

Regards,
Harini