Am 04.01.2018 um 12:44 schrieb Russell King - ARM Linux:
> On Thu, Jan 04, 2018 at 08:00:53AM +0100, Heiner Kallweit wrote:
>> Parameter mask of phy_modify() holds the bits to be cleared.
>> In the mentioned commit parameter mask seems to be inverted in
>> few cases, what IMO is wrong (see example).
>
> I'd be grateful if you could list those that you think are wrong please.
> For function __phy_modify documentation and implementation conflict.
Documentation states "(value & mask) | set" whilst implementation is
"(value & ~mask) | set". Based on the subsequent patches I assume
that your intention is what is documented.
Personally I find "ret & ~mask" more intuitive (see also set_mask_bits
in include/linux/bitops.h) but this may be a question of personal taste.
In kernel code both flavors are used.
+ * Unlocked helper function which allows a PHY register to be modified as
+ * new register value = (old register value & mask) | set
+ */
+int __phy_modify(struct phy_device *phydev, u32 regnum, u16 mask, u16 set)
+{
+ int ret, res;
+
+ ret = __phy_read(phydev, regnum);
+ if (ret >= 0) {
+ res = __phy_write(phydev, regnum, (ret & ~mask) | set);
+ if (res < 0)
+ ret = res;
+ }
+
+ return ret;
+}
Could you please advise whether documentation or implementation reflect
your intention? Then I'll check again which changes I'd consider to
be wrong.
Regards, Heiner
>> Maybe I miss something, could you please check?
>
> It's entirely possible that some are wrong - the patch started out as
> having the mask argument inverted, but during its evolution, that was
> corrected, and I thought all places had been updated - maybe they were
> initially wrong.
>
> I did go through the patch several times before sending it to try to
> ensure that it was correct, but must have overlooked some, because the
> one you quote is one I definitely looked at several times. It's highly
> likely that if I have another look through the patch, I still won't
> spot those that you've found.
>
>> And somehow related:
>> When adding such helpers, wouldn't it make sense to add
>> helpers for setting / clearing bits too? Something like:
>> phy_set_bits(phydev, reg, val) -> phy_modify(phydev, reg, 0, val)
>
> Maybe, but lets try and solve the problems with the existing patch
> first.
>
> Thanks for reporting this, and sorry for the hassle.
>
