Re: [PATCH v2 0/7] ath9k: EEPROM swapping improvements

[Martin Blumenstingl <martin.blumenstingl-gM/Ye1E23mwN+BqQ9rBEUg@public.gmane.org>]

On Fri, Nov 25, 2016 at 4:06 PM, Valo, Kalle <kvalo-A+ZNKFmMK5xy9aJCnZT0Uw@public.gmane.org> wrote:
> Kalle Valo <kvalo-sgV2jX0FEOL9JmXXK+q4OQ@public.gmane.org> writes:
>
>> Martin Blumenstingl <martin.blumenstingl-gM/Ye1E23mwN+BqQ9rBEUg@public.gmane.org> writes:
>>
>>> There are two types of swapping the EEPROM data in the ath9k driver.
>>> Before this series one type of swapping could not be used without the
>>> other.
>>>
>>> The first type of swapping looks at the "magic bytes" at the start of
>>> the EEPROM data and performs swab16 on the EEPROM contents if needed.
>>> The second type of swapping is EEPROM format specific and swaps
>>> specific fields within the EEPROM itself (swab16, swab32 - depends on
>>> the EEPROM format).
>>>
>>> With this series the second part now looks at the EEPMISC register
>>> inside the EEPROM, which uses a bit to indicate if the EEPROM data
>>> is Big Endian (this is also done by the FreeBSD kernel).
>>> This has a nice advantage: currently there are some out-of-tree hacks
>>> (in OpenWrt and LEDE) where the EEPROM has a Big Endian header on a
>>> Big Endian system (= no swab16 is performed) but the EEPROM itself
>>> indicates that it's data is Little Endian. Until now the out-of-tree
>>> code simply did a swab16 before passing the data to ath9k, so ath9k
>>> first did the swab16 - this also enabled the format specific swapping.
>>> These out-of-tree hacks are still working with the new logic, but it
>>> is recommended to remove them. This implementation is based on a
>>> discussion with Arnd Bergmann who raised concerns about the
>>> robustness and portability of the swapping logic in the original OF
>>> support patch review, see [0].
>>>
>>> After a second round of patches (= v1 of this series) neither Arnd
>>> Bergmann nor I were really happy with the complexity of the EEPROM
>>> swapping logic. Based on a discussion (see [1] and [2]) we decided
>>> that ath9k should use a defined format (specifying the endianness
>>> of the data - I went with __le16 and __le32) when accessing the
>>> EEPROM fields. A benefit of this is that we enable the EEPMISC based
>>> swapping logic by default, just like the FreeBSD driver, see [3]. On
>>> the devices which I have tested (see below) ath9k now works without
>>> having to specify the "endian_check" field in ath9k_platform_data (or
>>> a similar logic which could provide this via devicetree) as ath9k now
>>> detects the endianness automatically. Only EEPROMs which are mangled
>>> by some out-of-tree code still need the endian_check flag (or one can
>>> simply remove that mangling from the out-of-tree code).
>>>
>>> Testing:
>>> - tested by myself on AR9287 with Big Endian EEPROM
>>> - tested by myself on AR9227 with Little Endian EEPROM
>>> - tested by myself on AR9381 (using the ar9003_eeprom implementation,
>>>   which did not suffer from this whole problem)
>>> - how do we proceed with testing? maybe we could keep this in a
>>>   feature-branch and add these patches to LEDE once we have an ACK to
>>>   get more people to test this
>>>
>>> This series depends on my other series (v7):
>>> "add devicetree support to ath9k" - see [4]
>>
>> I think this looks pretty good. If there's a bug somewhere it should be
>> quite easy to fix so I'm not that worried and would be willing to take
>> these as soon as I have applied the dependency series. IIRC your
>> devicetree patches will have at least one more review round so that will
>> take some time still. In the meantime it would be great if LEDE folks
>> could take a look at these and comment (or test).
>
> So are everyone happy with this? I haven't seen any comments. If I don't
> here anything I'm planning to take these, most likely for 4.11.
after being busy due to <daytime job and other things in life> I'm
currently trying to get the patches into LEDE: [0] (so far there are
no major objections)
once we get this into LEDE we'll see pretty soon if there are any
problems or not -> 4.11 sounds good to me!


Regards,
Martin


[0] http://lists.infradead.org/pipermail/lede-dev/2016-November/004231.html