Re: [PATCH 5/6] phy: twl4030-usb: add support for reading resistor on ID pin.

[Kishon Vijay Abraham I <kishon@ti.com>]

Hi,

On Tuesday 02 June 2015 03:07 AM, NeilBrown wrote:
> On Mon, 1 Jun 2015 19:06:52 +0530 Kishon Vijay Abraham I <kishon@ti.com>
> wrote:
>
>> Hi,
>>
>> On Thursday 16 April 2015 01:33 PM, NeilBrown wrote:
>>> From: NeilBrown <neilb@suse.de>
>>>
>>> The twl4030 phy can measure, with low precision, the
>>> resistance-to-ground of the ID pin.
>>>
>>> Add a function to read the value, and export the result
>>> via sysfs.
>>
>> Little sceptical about adding new sysfs entries. Do you have a good reason to
>> add this?
>
> The hardware can report the value, so why not present it to user-space?
>
> I originally used this with a udev rule which would configure the maximum
> current based on the resistance measure - to work with the particular charger
> hardware I have.
>
> More recent patches try to do all of the max-current configuration in the
> kernel, so I could live without exporting the value via sysfs if that is a
> show-stopper.
>
> I can't see where the scepticism comes from though.  It is a well defined
> and cleary documented feature of the hardware.  Why not expose it?

ABI can never be removed or modified later. So should be really careful before 
adding it.

Thanks
Kishon

>
> Thanks,
> NeilBrown
>
>
>>
>> Thanks
>> Kishon
>>>
>>> If the read fails, which it does sometimes, try again in 50msec.
>>>
>>> Acked-by: Pavel Machek <pavel@ucw.cz>
>>> Signed-off-by: NeilBrown <neilb@suse.de>
>>> ---
>>>    .../ABI/testing/sysfs-platform-twl4030-usb         |   22 +++++++
>>>    drivers/phy/phy-twl4030-usb.c                      |   63 ++++++++++++++++++++
>>>    2 files changed, 85 insertions(+)
>>>
>>> diff --git a/Documentation/ABI/testing/sysfs-platform-twl4030-usb b/Documentation/ABI/testing/sysfs-platform-twl4030-usb
>>> index 512c51be64ae..425d23676f8a 100644
>>> --- a/Documentation/ABI/testing/sysfs-platform-twl4030-usb
>>> +++ b/Documentation/ABI/testing/sysfs-platform-twl4030-usb
>>> @@ -6,3 +6,25 @@ Description:
>>>    	Possible values: "on", "off".
>>>
>>>    	Changes are notified via select/poll.
>>> +
>>> +What: /sys/bus/platform/devices/*twl4030-usb/id
>>> +Description:
>>> +	Read-only report on measurement of USB-OTG ID pin.
>>> +
>>> +	The ID pin may be floating, grounded, or pulled to
>>> +	ground by a resistor.
>>> +
>>> +	A very course grained reading of the resistance is
>>> +	available.  The numbers given in kilo-ohms are roughly
>>> +	the center-point of the detected range.
>>> +
>>> +	Possible values are:
>>> +		ground
>>> +		102k
>>> +		200k
>>> +		440k
>>> +		floating
>>> +		unknown
>>> +
>>> +	"unknown" indicates a problem with trying to detect
>>> +	the resistance.
>>> diff --git a/drivers/phy/phy-twl4030-usb.c b/drivers/phy/phy-twl4030-usb.c
>>> index 3a707dd14238..1d6f3e70193e 100644
>>> --- a/drivers/phy/phy-twl4030-usb.c
>>> +++ b/drivers/phy/phy-twl4030-usb.c
>>> @@ -379,6 +379,56 @@ static void twl4030_i2c_access(struct twl4030_usb *twl, int on)
>>>    	}
>>>    }
>>>
>>> +enum twl4030_id_status {
>>> +	TWL4030_GROUND,
>>> +	TWL4030_102K,
>>> +	TWL4030_200K,
>>> +	TWL4030_440K,
>>> +	TWL4030_FLOATING,
>>> +	TWL4030_ID_UNKNOWN,
>>> +};
>>> +static char *twl4030_id_names[] = {
>>> +	"ground",
>>> +	"102k",
>>> +	"200k",
>>> +	"440k",
>>> +	"floating",
>>> +	"unknown"
>>> +};
>>> +
>>> +enum twl4030_id_status twl4030_get_id(struct twl4030_usb *twl)
>>> +{
>>> +	int ret;
>>> +
>>> +	pm_runtime_get_sync(twl->dev);
>>> +	if (twl->usb_mode == T2_USB_MODE_ULPI)
>>> +		twl4030_i2c_access(twl, 1);
>>> +	ret = twl4030_usb_read(twl, ULPI_OTG_CTRL);
>>> +	if (ret < 0 || !(ret & ULPI_OTG_ID_PULLUP)) {
>>> +		/* Need pull-up to read ID */
>>> +		twl4030_usb_set_bits(twl, ULPI_OTG_CTRL,
>>> +				     ULPI_OTG_ID_PULLUP);
>>> +		mdelay(50);
>>> +	}
>>> +	ret = twl4030_usb_read(twl, ID_STATUS);
>>> +	if (ret < 0 || (ret & 0x1f) == 0) {
>>> +		mdelay(50);
>>> +		ret = twl4030_usb_read(twl, ID_STATUS);
>>> +	}
>>> +
>>> +	if (twl->usb_mode == T2_USB_MODE_ULPI)
>>> +		twl4030_i2c_access(twl, 0);
>>> +	pm_runtime_put_autosuspend(twl->dev);
>>> +
>>> +	if (ret < 0)
>>> +		return TWL4030_ID_UNKNOWN;
>>> +	ret = ffs(ret) - 1;
>>> +	if (ret < TWL4030_GROUND || ret > TWL4030_FLOATING)
>>> +		return TWL4030_ID_UNKNOWN;
>>> +
>>> +	return ret;
>>> +}
>>> +
>>>    static void __twl4030_phy_power(struct twl4030_usb *twl, int on)
>>>    {
>>>    	u8 pwr = twl4030_usb_read(twl, PHY_PWR_CTRL);
>>> @@ -532,6 +582,16 @@ static ssize_t twl4030_usb_vbus_show(struct device *dev,
>>>    }
>>>    static DEVICE_ATTR(vbus, 0444, twl4030_usb_vbus_show, NULL);
>>>
>>> +static ssize_t twl4030_usb_id_show(struct device *dev,
>>> +				   struct device_attribute *attr,
>>> +				   char *buf)
>>> +{
>>> +	struct twl4030_usb *twl = dev_get_drvdata(dev);
>>> +	return scnprintf(buf, PAGE_SIZE, "%s\n",
>>> +			 twl4030_id_names[twl4030_get_id(twl)]);
>>> +}
>>> +static DEVICE_ATTR(id, 0444, twl4030_usb_id_show, NULL);
>>> +
>>>    static irqreturn_t twl4030_usb_irq(int irq, void *_twl)
>>>    {
>>>    	struct twl4030_usb *twl = _twl;
>>> @@ -709,6 +769,8 @@ static int twl4030_usb_probe(struct platform_device *pdev)
>>>    	platform_set_drvdata(pdev, twl);
>>>    	if (device_create_file(&pdev->dev, &dev_attr_vbus))
>>>    		dev_warn(&pdev->dev, "could not create sysfs file\n");
>>> +	if (device_create_file(&pdev->dev, &dev_attr_id))
>>> +		dev_warn(&pdev->dev, "could not create sysfs file\n");
>>>
>>>    	ATOMIC_INIT_NOTIFIER_HEAD(&twl->phy.notifier);
>>>
>>> @@ -753,6 +815,7 @@ static int twl4030_usb_remove(struct platform_device *pdev)
>>>    	pm_runtime_get_sync(twl->dev);
>>>    	cancel_delayed_work(&twl->id_workaround_work);
>>>    	device_remove_file(twl->dev, &dev_attr_vbus);
>>> +	device_remove_file(twl->dev, &dev_attr_id);
>>>
>>>    	/* set transceiver mode to power on defaults */
>>>    	twl4030_usb_set_mode(twl, -1);
>>>
>>>
>