linux-kernel - Re: [PATCH v3 10/16] usb: phy: tegra: Use device-tree notion of reset-GPIO's active-state

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Date:   Sat, 4 Jan 2020 02:53:24 +0300
From:   Dmitry Osipenko <digetx@...il.com>
To:     Michał Mirosław <mirq-linux@...e.qmqm.pl>
Cc:     Rob Herring <robh+dt@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Peter Chen <Peter.Chen@....com>,
        Thierry Reding <thierry.reding@...il.com>,
        Jonathan Hunter <jonathanh@...dia.com>,
        Felipe Balbi <balbi@...nel.org>, devicetree@...r.kernel.org,
        linux-usb@...r.kernel.org, linux-tegra@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 10/16] usb: phy: tegra: Use device-tree notion of
 reset-GPIO's active-state

03.01.2020 10:58, Michał Mirosław пишет:
> On Sat, Dec 28, 2019 at 11:33:52PM +0300, Dmitry Osipenko wrote:
> [...]
>>  static int ulpi_open(struct tegra_usb_phy *phy)
>>  {
>> -	int err;
>> -
>> -	err = gpio_direction_output(phy->reset_gpio, 0);
>> -	if (err) {
>> -		dev_err(phy->u_phy.dev,
>> -			"ULPI reset GPIO %d direction not deasserted: %d\n",
>> -			phy->reset_gpio, err);
>> -		return err;
>> -	}
>> +	gpiod_set_value_cansleep(phy->reset_gpio, 1);
>>  
>>  	return 0;
>>  }
> 
> The message now removed seems inverted to the meaning of the code. Is
> this a bug, or the reset really should be asserted here?

The removed message was added in patch #2 and indeed it should say
"asserted". Good catch, thanks!

> I can see that
> it is deasserted in phy_power_up, but that goes before or after ulpi_open()?

The ulpi_phy_power_on happens after the ulpi_open, please take a look at
tegra_usb_phy_init().

> After the change below, the reset is asserted at probe() time now.

Yes, the probe now asserts the reset. It is an intended change because
it should be a bit better to explicitly per-initialize the GPIO state to
an expected state during of the GPIO retrieval, like most of other
drivers do and which should be a "generic/common way".

Actually, the reset assertion of ulpi_open() could be removed safely now
since it doesn't do anything useful, given that probe asserts the reset.

> [...]
>> -		err = devm_gpio_request(&pdev->dev, tegra_phy->reset_gpio,
>> -					"ulpi_phy_reset_b");
>> +		gpiod = devm_gpiod_get_from_of_node(&pdev->dev, np,
>> +						    "nvidia,phy-reset-gpio",
>> +						    0, GPIOD_OUT_HIGH,
>> +						    "ulpi_phy_reset_b");
>> +		err = PTR_ERR_OR_ZERO(gpiod);
>>  		if (err) {
>> -			dev_err(&pdev->dev, "Request failed for GPIO %d: %d\n",
>> -				tegra_phy->reset_gpio, err);
>> +			dev_err(&pdev->dev,
>> +				"Request failed for reset GPIO: %d\n", err);
>>  			return err;
>>  		}
>> +		tegra_phy->reset_gpio = gpiod;
> 
> A nice extension to kernel's printf - "%pe" format - has just landed in
> Linus' master tree.

Thank you very much, I didn't know about that.

I'll prepare v4 with the above things addressed, thank you again and
please let me know if you'll spot anything else!