On Mon, Nov 01, 2021 at 11:33:07AM -0700, Trent Piepho wrote:
> On Mon, Nov 1, 2021 at 2:01 AM Sascha Hauer <[1]sha@xxxxxxxxxxxxxx> wrote:
> > On Wed, Oct 20, 2021 at 10:39:54AM +0200, Daniel Brát wrote:
> > > Make 'phy_optional_get' return NULL instead of ERR_PTR(-ENOSYS) when
> the
> > > CONFIG_GENERIC_PHY is not enabled. It makes more sense to return NULL
> instead
> > > of straight up throwing a error since the function has 'optional' in
> its name.
> > > This also fixes dwc2 usb driver which would previously fail inside its
> probe
> > > function despite being able to function without a phy just fine.
> >
> > The phy is only optional as long as none is specified in the device
> > tree. When there is one specified then it's no longer optional. We can't
> > do the right thing here without checking the device tree. Given that
> > it's simple to enable CONFIG_GENERIC_PHY I think this is the way to go.
>
> But this force enables GENERIC_PHY when it's not needed.
>
> There are commonly many device nodes in Linux dts files that are not used
> by an enabled Barebox driver. It's normal to turn off a driver that might
> be or could be used. Is it necessarily an error if a phy is present in
> the dts but we don't wish to include support for it?
We need to distinguish the cases "There is a phy specified, but the
reset defaults are good enough to go without a driver" and "There is a
phy specified and we need driver support for it". barebox can't know
this.
Returning NULL from the phy_optional_get() stub has another problem:
Some devices might work with CONFIG_GENERIC_PHY disabled, but stop
to work when CONFIG_GENERIC_PHY gets enabled, because we might have
no driver for the phy. Having boards that only work with CONFIG_GENERIC_PHY
disabled is rather unexpected as well.
> struct phy *phy_optional_get(struct device_d *dev, const char *string)
> {
> if (dev->device_node &&
> !of_parse_phandle_with_args(dev->device_node, "phys",
> "#phy-cells", of_property_match_string(dev->device_node, "phy-names",
> string), NULL))
> dev_warn(dev, "%s phy specified in device tree but
> CONFIG_GENERIC_PHY support is not enabled", string);
> return NULL;
> }
I am fine with this approach. We could add a check if the phy node has a
status = "disabled" property. That would allow a board to explicitly
state that we do not need to support a phy. We could then do the
right thing no matter if CONFIG_GENERIC_PHY is enabled or not.
Thinking about it I would prefer something like barebox,status = "disabled"
to prevent the property from leaking into Linux.
Sascha
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