ptp: Make max_phase_adjustment sysfs device attribute invisible when not supported

The .adjphase operation is an operation that is implemented only by certain
PHCs. The sysfs device attribute node for querying the maximum phase
adjustment supported should not be exposed on devices that do not support
.adjphase.

Fixes: c3b60ab7 ("ptp: Add .getmaxphase callback to ptp_clock_info")
Signed-off-by: Rahul Rameshbabu <rrameshbabu@nvidia.com>
Reported-by: Nathan Chancellor <nathan@kernel.org>
Reported-by: Naresh Kamboju <naresh.kamboju@linaro.org>
Reported-by: Linux Kernel Functional Testing <lkft@linaro.org>
Link: https://lore.kernel.org/netdev/20230627162146.GA114473@dev-arch.thelio-3990X/
Link: https://lore.kernel.org/all/CA+G9fYtKCZeAUTtwe69iK8Xcz1mOKQzwcy49wd+imZrfj6ifXA@mail.gmail.com/Tested-by: Nathan Chancellor <nathan@kernel.org>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Acked-by: Richard Cochran <richardcochran@gmail.com>
Reviewed-by: Petr Vorel <pvorel@suse.cz>
Message-ID: <20230627232139.213130-1-rrameshbabu@nvidia.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/ptp/ptp_sysfs.c

@@ -358,6 +358,9 @@ static umode_t ptp_is_attribute_visible(struct kobject *kobj,
 		   attr == &dev_attr_max_vclocks.attr) {
 		if (ptp->is_virtual_clock)
 			mode = 0;
+	} else if (attr == &dev_attr_max_phase_adjustment.attr) {
+		if (!info->adjphase || !info->getmaxphase)
+			mode = 0;
 	}
 
 	return mode;