[ath9k-devel] [RFC 0/3] of: add common bindings to (de)activate IEEE 802.11 bands

[Martin Blumenstingl <martin.blumenstingl@googlemail.com>]

On Wed, Oct 5, 2016 at 10:31 PM, Rob Herring <robh+dt@kernel.org> wrote:
> On Wed, Oct 5, 2016 at 1:36 PM, Felix Fietkau <nbd@nbd.name> wrote:
>> On 2016-10-05 20:25, Martin Blumenstingl wrote:
>>> On Mon, Oct 3, 2016 at 5:22 PM, Rob Herring <robh+dt@kernel.org> wrote:
>>>> On Sun, Oct 2, 2016 at 5:50 PM, Martin Blumenstingl
>>>> <martin.blumenstingl@googlemail.com> wrote:
>>>>> There are at least two drivers (ath9k and mt76) out there, where
>>>>> devicetree authors need to override the enabled bands.
>>>>>
>>>>> For ath9k there is only one use-case: disabling a band which has been
>>>>> incorrectly enabled by the vendor in the EEPROM (enabling a band is not
>>>>> possible because the calibration data would be missing in the EEPROM).
>>>>> The mt76 driver (currently pending for review) however allows enabling
>>>>> and disabling the 2.4GHz and 5GHz band, see [0].
>>>>>
>>>>> Based on the discussion of (earlier versions of) my ath9k devicetree
>>>>> patch it was suggested [1] that we use enable- and disable- properties.
>>>>> The current patch implements:
>>>>> - bands can be enabled or disabled with the corresponding property
>>>>> - if both (disable and enable) properties are given and a driver asks
>>>>>   whether the band is enabled then the logic will return false (= not
>>>>>   enabled, preferring the disabled flag)
>>>>> - if both (disable and enable) properties are given and a driver asks
>>>>>   whether the band is disabled then the logic will return true (again,
>>>>>   preferring the disabled flag over the enabled flag)
>>>>>
>>>>> We can still change the logic to do what the mt76 driver does (I am
>>>>> fine with both solutions):
>>>>> - property not available: driver decides which bands to enable
>>>>> - property set to 0: disable the band
>>>>> - property set to 1: enable the band
>>>>
>>>> I prefer this way. Really, I'd prefer just a boolean disable property.
>>>> I'm not sure why you need the enable. We usually have these tri-state
>>>> properties when you want not present to mean use the bootloader or
>>>> default setting. Try to make not present the most common case.
>>> Felix: could you please give a few details why mt76 can not only
>>> disable but also enable a specific band?
>>> There is no specific comment in the sources [0] why this is needed.
>>> All other drivers that I am aware of (ath9k, rt2x00) only allow
>>> disabling a specific band, they never enable it (this has to be done
>>> explicitly by the EEPROM).
>> None of the devices use it at the moment, I probably added it when I
>> played with a device that had broken EEPROM data. I guess I decided to
>> do it this way because on many devices the band capability field simply
>> cannot be trusted.
>> I guess I would be okay with just having a disable property and adding
>> an enable property later only if we end up actually needing it.
>
> If EEPROM is commonly wrong or missing, then seems like you want to
> plan ahead and support both enable and disable.
if we want to plan ahead we could use two properties "ieee80211-2ghz"
and "ieee80211-5ghz", each of them allows the values: 0 = disabled, 1
= enabled, absent = auto-detect (for example based on the card's
EEPROM), any other value is invalid

How should our API look in this case?
Would we still have bool ..._enabled() and bool ..._disabled() - what
if the property is absent (would we add another boolean
ieee80211_is_[2,5]ghz_configured(np) to handle that)?
We could also introduce int ieee80211_get_[2,5]ghz_enabled(struct
device_node *np, bool *enabled) and leave it up to the caller?


Regards,
Martin