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

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);
> >
> >

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