Date:	Tue, 27 Jan 2015 09:38:01 -0800
From:	David Cohen <david.a.cohen@...ux.intel.com>
To:	Heikki Krogerus <heikki.krogerus@...ux.intel.com>
Cc:	Felipe Balbi <balbi@...com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Baolu Lu <baolu.lu@...ux.intel.com>, linux-usb@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Kishon Vijay Abraham I <kishon@...com>
Subject: Re: [PATCH 8/8] phy: add driver for TI TUSB1210 ULPI PHY

On Tue, Jan 27, 2015 at 11:28:56AM +0200, Heikki Krogerus wrote:
> On Mon, Jan 26, 2015 at 11:23:37AM -0800, David Cohen wrote:
> > On Mon, Jan 26, 2015 at 02:55:03PM +0200, Heikki Krogerus wrote:
> > > On Sat, Jan 24, 2015 at 03:58:11PM -0800, David Cohen wrote:
> > > > > +static int tusb1210_power_on(struct phy *phy)
> > > > > +{
> > > > > +	struct tusb1210 *tusb = phy_get_drvdata(phy);
> > > > > +
> > > > > +	gpiod_set_value_cansleep(tusb->gpio_reset, 1);
> > > > > +	gpiod_set_value_cansleep(tusb->gpio_cs, 1);
> > > > > +
> > > > > +	/* Restore eye diagram optimisation value */
> > > > > +	ulpi_write(tusb->ulpi, TUSB1210_VENDOR_SPECIFIC2,
> > > > > +		   tusb->eye_diagram_tuning);
> > > > 
> > > > After you power on phy, ulpi bus may not be available right away. In
> > > > intel case, phy power on happens during dwc3 power on. ULPI bus is not
> > > > available until OTG controller and phy are in sync.
> > > > 
> > > > In resume, you can't restore eye diagram from here.
> > > 
> > > I'm sorry but I don't think I understand? Where do we power on the phy
> > > before dwc3 is powered on? Or is this a Baytrail-CR specific problem?
> > > I can't see any problems with the hardware I have.
> > 
> > You can't see in single accesses. But you may see when running stability
> > tests overnight.
> > 
> > Anyway, look for dwc3_core_soft_reset() function:
> > - dwc3 goes to reset state
> > - phy is initialized (or at least gets ready to sync clocks)
> > - dwc3 goes out or reset state
> 
> And if you look at dwc3_probe, you'll notice that it calls
> phy_power_on after that, and ulpi will most definitely be accessible
> at that point.
> 
> I'm only using the init and exit hooks instead of just
> power_on/power_off because I'm not sure which the controllers will
> use. For example, now dwc3 calls phy_init() in it's resume routine and
> not phy_power_on() like I would expect. I know the problem has been
> pointed out by others, so I'm expecting we'll get guidelines for it
> later. But before we do, I see no harm in having both init and
> power_on hooks in this driver.

It sounds hackish to me. You could clearly change the logic on
init/power_on callbacks to avoid this problem.

> 
> > During tusb1210 phy init from dwc3, you shouldn't access ulpi bus.
> 
> We will end up executing one failed write followed by write that we
> know will succeed. Ideally we didn't have to do the first one at all,
> but I don't see any risk here.

Ditto.

> 
> > > > > +	gpio = devm_gpiod_get(&ulpi->dev, "cs");
> > > > > +	if (!IS_ERR(gpio)) {
> > > > > +		ret = gpiod_direction_output(gpio, 0);
> > > > > +		if (ret)
> > > > > +			return ret;
> > > > > +		tusb->gpio_cs = gpio;
> > > > > +	}
> > > > > +
> > > > > +	/* Store initial eye diagram optimisation value */
> > > > > +	ret = ulpi_read(ulpi, TUSB1210_VENDOR_SPECIFIC2);
> > > > 
> > > > It's unclear if ulpi is accessible at this point. You can't read it at
> > > > this point.
> > > 
> > > We wouldn't have reached this point if ulpi wasn't accessible.
> > > Registering the ulpi interface would have already failed so no driver
> > > would have been probed.
> > 
> > You have a chicken/egg problem here:
> > - dwc3 needs phy to complete soft reset during probe
> > - tusb1210 needs dwc3 soft reset completed to be accessible via ULPI
> > 
> > Can you share how tusb1210 is connected on the platform you're using as
> > test for this patch? I don't think this driver would work reliably with
> > this device:
> > http://liliputing.com/2014/11/trekstor-launches-first-android-tablet-based-intels-irda-reference-design.html
> 
> The only reason why that board doesn't work is because of very much
> Baytrail-CR specific problems. These are are two issues, but the first

That's not BYT-CR specific problems. That's just dwc3 and tusb1210
interacting as they're expecting to.

> one is critical for getting it working. Both will be handled, but
> separately from this set:
> 
> 1) The firmware leaves the PHY in reset, forcing us to enable it
> somehow in OS before accessing ulpi. Unless we can get a firmware fix
> for that (it's starting to look like it's not going to happen; please
> correct me if you know something else!), we need to add a quirk for
> Baytrails (attached), which is probable still OK. But IMO this really
> should be fixed in the firmware.

It seems you're expecting the PHY to be fully operational in order to
probe it. That's wrong assumption. BYT-CR's BIOS is doing nothing wrong
by leaving PHY on reset state. The real problem is what I stated above.
With your current logic, you'll get stuck with checking/egg problem: you
need phy probed to probe dwc3, but need dwc3 probed to power on phy.
You need a logic to break this circular dependency.

> 
> 2) Since the gpio resources are given to the controller device in ACPI
> tables and there isn't separate device object for the PHY at all, we
> need to deliver the gpios somehow separately to the phy driver. There
> is a thread where we are talking about how to do that:
> https://lkml.org/lkml/2014/12/18/82

How about just leave the logic the way it is:
dwc3-pci.c registers platform_device with gpio as resource if the GPIOs
are provided to dwc3. If not, then dwc3-pci.c will expect phy to have
its own ACPI id.

Br, David

> 
> 
> Thanks,
> 
> -- 
> heikki

> diff --git a/drivers/usb/dwc3/dwc3-pci.c b/drivers/usb/dwc3/dwc3-pci.c
> index 8d95056..53902ea 100644
> --- a/drivers/usb/dwc3/dwc3-pci.c
> +++ b/drivers/usb/dwc3/dwc3-pci.c
> @@ -21,6 +21,7 @@
>  #include <linux/slab.h>
>  #include <linux/pci.h>
>  #include <linux/platform_device.h>
> +#include <linux/gpio/consumer.h>
>  
>  #include "platform_data.h"
>  
> @@ -35,6 +36,24 @@
>  
>  static int dwc3_pci_quirks(struct pci_dev *pdev)
>  {
> +	if (pdev->vendor == PCI_VENDOR_ID_INTEL &&
> +	    pdev->device == PCI_DEVICE_ID_INTEL_BYT) {
> +		struct gpio_desc *gpio;
> +
> +		gpio = gpiod_get_index(&pdev->dev, "reset", 0);
> +		if (!IS_ERR(gpio)) {
> +			gpiod_direction_output(gpio, 0);
> +			gpiod_set_value_cansleep(gpio, 1);
> +			gpiod_put(gpio);
> +		}
> +		gpio = gpiod_get_index(&pdev->dev, "cs", 1);
> +		if (!IS_ERR(gpio)) {
> +			gpiod_direction_output(gpio, 0);
> +			gpiod_set_value_cansleep(gpio, 1);
> +			gpiod_put(gpio);
> +		}
> +	}
> +
>  	if (pdev->vendor == PCI_VENDOR_ID_AMD &&
>  	    pdev->device == PCI_DEVICE_ID_AMD_NL_USB) {
>  		struct dwc3_platform_data pdata;

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