Re: [PATCH 04/14] usb: phy: nop: Handle power supply regulator for the PHY

Roger Quadros
2013-01-14T11:51:21Z

On 01/14/2013 01:25 PM, Russell King - ARM Linux wrote:
> On Mon, Jan 14, 2013 at 11:54:42AM +0200, Roger Quadros wrote:
>> On 01/11/2013 07:17 PM, Russell King - ARM Linux wrote:
>>> On Thu, Jan 10, 2013 at 06:51:24PM +0200, Roger Quadros wrote:
>>>> We use "vcc" as the supply name for the PHY's power supply.
>>>> The power supply will be enabled during .init() and disabled
>>>> during .shutdown()
>>>>
>>>> Signed-off-by: Roger Quadros <rogerq@ti.com>
>>>> ---
>>>> drivers/usb/otg/nop-usb-xceiv.c | 18 ++++++++++++++++++
>>>> 1 files changed, 18 insertions(+), 0 deletions(-)
>>>>
>>>> diff --git a/drivers/usb/otg/nop-usb-xceiv.c b/drivers/usb/otg/nop-usb-xceiv.c
>>>> index 163f972..1c6db10 100644
>>>> --- a/drivers/usb/otg/nop-usb-xceiv.c
>>>> +++ b/drivers/usb/otg/nop-usb-xceiv.c
>>>> @@ -33,11 +33,13 @@
>>>> #include <linux/usb/nop-usb-xceiv.h>
>>>> #include <linux/slab.h>
>>>> #include <linux/clk.h>
>>>> +#include <linux/regulator/consumer.h>
>>>>
>>>> struct nop_usb_xceiv {
>>>> struct usb_phy phy;
>>>> struct device *dev;
>>>> struct clk *clk;
>>>> + struct regulator *vcc;
>>>> };
>>>>
>>>> static struct platform_device *pd;
>>>> @@ -70,6 +72,11 @@ static int nop_init(struct usb_phy *phy)
>>>> {
>>>> struct nop_usb_xceiv *nop = dev_get_drvdata(phy->dev);
>>>>
>>>> + if (nop->vcc) {
>>>> + if (regulator_enable(nop->vcc))
>>>> + dev_err(phy->dev, "Failed to enable power\n");
>>>> + }
>>>> +
>>>> if (nop->clk)
>>>> clk_enable(nop->clk);
>>>>
>>>> @@ -82,6 +89,11 @@ static void nop_shutdown(struct usb_phy *phy)
>>>>
>>>> if (nop->clk)
>>>> clk_disable(nop->clk);
>>>> +
>>>> + if (nop->vcc) {
>>>> + if (regulator_disable(nop->vcc))
>>>> + dev_err(phy->dev, "Failed to disable power\n");
>>>> + }
>>>> }
>>>>
>>>> static int nop_set_peripheral(struct usb_otg *otg, struct usb_gadget *gadget)
>>>> @@ -157,6 +169,12 @@ static int nop_usb_xceiv_probe(struct platform_device *pdev)
>>>> }
>>>> }
>>>>
>>>> + nop->vcc = devm_regulator_get(&pdev->dev, "vcc");
>>>> + if (IS_ERR(nop->vcc)) {
>>>> + dev_dbg(&pdev->dev, "Error getting vcc regulator\n");
>>>> + nop->vcc = NULL;
>>>> + }
>>>
>>> Is it really appropriate for drivers to do this kind of thing with
>>> pointer-returning functions (I mean, setting the pointer to NULL on
>>> error, rather than just using a test for IS_ERR() in the above
>>> locations). You are imposing driver-local assumptions on an API.
>>>
>>> Practically it probably doesn't make much difference but given the
>>> amount of mistakes that we have with IS_ERR_OR_NULL()...
>>>
>> Makes sense. I'll convert it to use IS_ERR_OR_NULL() throughout.
>
> IS_ERR_OR_NULL() is going to be deprecated and removed. Please take a
> look at how these APIs work.

OK. I misunderstood what you meant earlier.

>
> If regulator support is not enabled, then devm_regulator_get() returns
> NULL, and all the other regulator functions become no-ops. This is not
> an error. Do you need the driver to error out if CONFIG_REGULATOR is
> disabled?
>
No, in fact even if CONFIG_REGULATOR is enabled and regulator_get()
fails, we just print a debug message and continue as usual. So
CONFIG_REGULATOR disabled _and_ regulator_get() error are handled in the
same way.

> If regulator support is enabled, then it can return a pointer-error
> value (as defined when IS_ERR() is true, and _in that case only_ can it
> be decoded by PTR_ERR() - PTR_ERR() is _only_ valid when IS_ERR()
> returns true - it is _not_ valid for all the cases that IS_ERR_OR_NULL()
> returns true.) Otherwise, it returns a cookie as far as the driver is
> concerned for the regulator suitable for passing into the other regulator
> APIs.
>
> By having the driver do something different, and make use of NULL as its
> own special sentinel, it's placing additional interpretations on the API,
> which can lead to bugs. Don't do this.

Agreed.

>
> If you can start making use of 'nop' vcc/clk members before they've been
> "got" then initialize them to ERR_PTR(-EINVAL) first.
>
> Also consider that when using the devm interfaces, you can do:
>
>
> nop->clk = devm_clk_get(&pdev->dev, ...);
> nop->vcc = devm_regulator_get(&pdev->dev, "vcc");
>
> if (IS_ERR(nop->clk))
> dev_dbg(&pdev->dev, "unable to get clock: %d\n",
> PTR_ERR(nop->clk));
>
> if (IS_ERR(nop->vcc))
> dev_dbg(&pdev->dev, "unable to get vcc regulator: %d\n",
> PTR_ERR(nop->vcc));
> ...
> if (!IS_ERR(nop->clk))
> clk_enable(nop->clk);

OK I get it now. The only case where nop->clk or nop->vcc will be NULL
is if the framework is not enabled. It is fine to call the
regulator/clock APIs with NULL pointers in that case.

>
> You may also consider that if you're going to print a warning for
> regulator_enable(), that you should print the error code as well, so that
> you know the reason why the failure happened.

OK.
>
> Also consider... is dev_err() appropriate for an "error", for which you
> print a message and continue as if nothing went wrong. To me that sounds
> more like a warning than an error, so maybe dev_warn() would be more
> appropriate?
>
I used dev_dbg(), because we don't treat not getting the power supply
regulator as that serious.

--
cheers,
-roger