linux-kernel - Re: [PATCH V3] net: emac: emac gigabit ethernet controller driver

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Date:	Fri, 8 Apr 2016 02:53:17 +0200
From:	Andrew Lunn <andrew@...n.ch>
To:	Timur Tabi <timur@...eaurora.org>
Cc:	Rob Herring <robh@...nel.org>,
	Gilad Avidov <gavidov@...eaurora.org>,
	netdev <netdev@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	linux-arm-msm <linux-arm-msm@...r.kernel.org>,
	Sagar Dharia <sdharia@...eaurora.org>, shankerd@...eaurora.org,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	vikrams@...eaurora.org, Christopher Covington <cov@...eaurora.org>
Subject: Re: [PATCH V3] net: emac: emac gigabit ethernet controller driver

On Thu, Apr 07, 2016 at 04:43:47PM -0500, Timur Tabi wrote:
> On my platform, firmware (UEFI) configures all of the GPIOs.  I need
> to get confirmation, but it appears that we don't actually make any
> GPIO calls at all.  I see code that looks like this:
> 
> 	for (i = 0; (!adpt->no_mdio_gpio) && i < EMAC_NUM_GPIO; i++) {
> 		gpio_info = &adpt->gpio_info[i];
> 		retval = of_get_named_gpio(node, gpio_info->name, 0);
> 		if (retval < 0)
> 			return retval;
> 
> And on our ACPI system, adpt->no_mdio_gpio is always true:
> 
> 	/* Assume GPIOs required for MDC/MDIO are enabled in firmware */
> 	adpt->no_mdio_gpio = true;

There are two different things here. One is configuring the pin to be
a GPIO. The second is using the GPIO as a GPIO. In this case,
bit-banging the MDIO bus.

The firmware could be doing the configuration, setting the pin as a
GPIO. However, the firmware cannot be doing the MDIO bit-banging to
make an MDIO bus available. Linux has to do that.

Or it could be we have all completely misunderstood the hardware, and
we are not doing bit-banging GPIO MDIO. There is a real MDIO
controller there, we don't use these pins as GPIOs, etc....

	   Andrew