Re: Re: [PATCH V4 net-bugfixs] net/ethernet: Update ret when ptp_clock is ERROR

On Thu, Nov 12, 2020 at 7:19 PM Richard Cochran
[off-list ref] wrote:

On Thu, Nov 12, 2020 at 09:25:12AM +0100, Arnd Bergmann wrote:

quoted

This is not really getting any better. If Richard is worried about
Kconfig getting changed here, I would suggest handling the
case of PTP being disabled by returning an error early on in the
function, like

struct am65_cpts *am65_cpts_create(struct device *dev, void __iomem *regs,
                                   struct device_node *node)
{
        struct am65_cpts *cpts;
        int ret, i;

        if (!IS_ENABLED(CONFIG_PTP_1588_CLOCK))
                 return -ENODEV;

No, please, no.  That only adds confusion.  The NULL return value
already signals that the compile time support was missing.  That was
the entire point of this...

 * ptp_clock_register() - register a PTP hardware clock driver
 *
 * @info:   Structure describing the new clock.
 * @parent: Pointer to the parent device of the new clock.
 *
 * Returns a valid pointer on success or PTR_ERR on failure.  If PHC
 * support is missing at the configuration level, this function
 * returns NULL, and drivers are expected to gracefully handle that
 * case separately.

The problem is that the caller doesn't handle that case gracefully,
but it instead wants to return an error after all. I don't see a good
solution either; as far as I'm concerned we should never be building
code that fails if PTP_1588_CLOCK is disabled when it cannot
do anything sensible in that configuration.

I agree that the 'imply' keyword in Kconfig is what made this a
lot worse, and it would be best to replace that with normal
dependencies.

It would be possible to have a ptp_clock_register_optional()
interface in addition to ptp_clock_register(), which could then
be changed to return an error. Some other subsystems follow
this pattern, but it's not any less confusing either.

     Arnd