staging: wfx: update TODO

This is a list of things that need to be done to get this driver out of the

staging directory.

  - I have to take a decision about secure link support. I can:

      - drop completely

      - keep it in an external patch (my preferred option)

      - replace call to mbedtls with kernel crypto API (necessitate a

        bunch of work)

      - pull mbedtls in kernel (non-realistic)

  - mac80211 interface does not (yet) have expected quality to be placed

    outside of staging:

      - Some processings are redundant with mac80211 ones

      - Many members from wfx_dev/wfx_vif can be retrieved from mac80211

        structures

      - Some functions are too complex

      - ...

  - Allocation of "link ids" is too complex. Allocation/release of link ids from

    sta_add()/sta_remove() should be sufficient.

  - The path for packets with IEEE80211_TX_CTL_SEND_AFTER_DTIM flags should be

    cleaned up. Currently, the process involve multiple work structs and a

    timer. It could be simplifed. In add, the requeue mechanism triggers more

    frequently than it should.

  - All structures defined in hif_api_*.h are intended to sent/received to/from

    hardware. All their members whould be declared __le32 or __le16. These

    structs should only been used in files named hif_* (and maybe in data_*.c).

    The upper layers (sta.c, scan.c etc...) should manage mac80211 structures.

    See:

       https://lore.kernel.org/lkml/20191111202852.GX26530@ZenIV.linux.org.uk

  - Once previous item done, it will be possible to audit the driver with

    `sparse'. It will probably find tons of problems with big endian

    architectures.

  - hif_api_*.h whave been imported from firmware code. Some of the structures

    are never used in driver.

  - Driver try to maintains power save status of the stations. However, this

    work is already done by mac80211. sta_asleep_mask and pspoll_mask should be

    dropped.

  - wfx_tx_queues_get() should be reworked. It currently try compute itself the

    QoS policy. However, firmware already do the job. Firmware would prefer to

    have a few packets in each queue and be able to choose itself which queue to

    use.

  - As suggested by Felix, rate control could be improved following this idea:

        https://lore.kernel.org/lkml/3099559.gv3Q75KnN1@pc-42/

  - When driver is about to loose BSS, it forge its own Null Func request (see

    wfx_cqm_bssloss_sm()). It should use mechanism provided by mac80211.

  - AP is actually is setup after a call to wfx_bss_info_changed(). Yet,

    ieee80211_ops provide callback start_ap().

  - The current process for joining a network is incredibly complex. Should be

    reworked.

  - Monitoring mode is not implemented despite being mandatory by mac80211.

  - "compatible" value are not correct. They should be "vendor,chip". See:

       https://lore.kernel.org/driverdev-devel/5226570.CMH5hVlZcI@pc-42

  - The "state" field from wfx_vif should be replaced by "vif->type".

  - It seems that wfx_upload_keys() is useless.

  - "event_queue" from wfx_vif seems overkill. These event are rare and they

     probably could be handled in a simpler fashion.

  - Feature called "secure link" should be either developed (using kernel

    crypto API) or dropped.

  - In wfx_cmd_send(), "async" allow to send command without waiting the reply.

    It may help in some situation, but it is not yet used. In add, it may cause

    some trouble:

      https://lore.kernel.org/driverdev-devel/alpine.DEB.2.21.1910041317381.2992@hadrien/

    So, fix it (by replacing the mutex with a semaphore) or drop it.

  - Chip support P2P, but driver does not implement it.

  - Chip support kind of Mesh, but driver does not implement it.