Re: [PATCH v8 6/8] wifi: ath12k: Introduce device group abstraction

[Kalle Valo <kvalo@kernel.org>]

Harshitha Prem <quic_hprem@quicinc.com> writes:

> From: Karthikeyan Periyasamy <quic_periyasa@quicinc.com>
>
> Currently, single device is probed and once firmware is ready, the device
> is registered to mac80211. For multi-link operation, different bands of
> different devices or same device would be part of a single wiphy and for
> this, hardware device group abstraction would be helpful.
>
> Hardware device group abstraction - when there are multiple devices (with
> single radio or dual radio) that are connected by any means of interface
> for communicating between them, then these devices can be combined
> together as a single group using a group id to form a group abstraction
> and register to mac80211.
>
> The grouping information of multiple devices would be based on device tree
> during device probe. If no such information is available then a single
> device will be part of group abstraction and registered to mac80211 else
> multiple devices advertised in device tree are combined and then registered
> to mac80211.
>
> For device group abstraction, a base structure named ath12k_hw_group (ag)
> and the following helpers are introduced:
>         ath12k_core_hw_group_alloc()    : allocate ath12k_hw_group (ag)
>                                           based on group id and number
>                                           of devices that are going to
>                                           be part of this group.
>         ath12k_core_hw_group_free()     : free ag during deinit.
>         ath12k_core_assign_hw_group()   : assign/map the details of group
>                                           to ath12k_base (ab).
>         ath12k_core_unassign_hw_group() : unassign/unmap the details of ag
>                                           in ath12k_base (ab).
>         ath12k_core_hw_group_create()   : create the devices which are part
>                                           of group (ag).
>         ath12k_core_hw_group_destroy()  : cleanup the devices in ag
>
> These helpers are used during device probe and mapping the group to the
> devices involved.
>
> Please find the illustration of how multiple devices might be combined
> together in future based on group id.
>
>                 Grouping of multiple devices (in future)
>
> +------------------------------------------------------------------------+
> |  +-------------------------------------+       +-------------------+   |
> |  |   +-----------+ | | +-----------+   |       |   +-----------+   |   |
> |  |   | ar (2GHz) | | | | ar (5GHz) |   |       |   | ar (6GHz) |   |   |
> |  |   +-----------+ | | +-----------+   |       |   +-----------+   |   |
> |  |          ath12k_base (ab)           |       | ath12k_base (ab)  |   |
> |  |         (Dual band device)          |       |                   |   |
> |  +-------------------------------------+       +-------------------+   |
> |                 ath12k_hw_group (ag) based on group id                 |
> +------------------------------------------------------------------------+

This is a good diagram, thanks for that. But how does struct ath12k_hw
fit into the diagram?

> In the above representation, two devices are combined into single group
> based on group id.
>
> Add base code changes where single device would be part of a group with an
> invalid group id forming an group abstraction. Multi device grouping will
> be introduced in future.
>
> Tested-on: QCN9274 hw2.0 PCI WLAN.WBE.1.0.1-00029-QCAHKSWPL_SILICONZ-1
> Tested-on: WCN7850 hw2.0 PCI
> WLAN.HMT.1.0-03427-QCAHMTSWPL_V1.0_V2.0_SILICONZ-1.15378.4
>
> Signed-off-by: Karthikeyan Periyasamy <quic_periyasa@quicinc.com>
> Co-developed-by: Harshitha Prem <quic_hprem@quicinc.com>
> Signed-off-by: Harshitha Prem <quic_hprem@quicinc.com>
> Acked-by: Jeff Johnson <quic_jjohnson@quicinc.com>

Like I have said before, for adding any new locks there needs to be a
proper analysis for the locking and good justifications why new locks
are needed. I don't see any of that above.

BTW I will from now on require proper analysis also for additions to
enum ath12k_dev_flags.

> --- a/drivers/net/wireless/ath/ath12k/core.c
> +++ b/drivers/net/wireless/ath/ath12k/core.c
> @@ -21,6 +21,9 @@ unsigned int ath12k_debug_mask;
>  module_param_named(debug_mask, ath12k_debug_mask, uint, 0644);
>  MODULE_PARM_DESC(debug_mask, "Debugging mask");
>  
> +static DEFINE_MUTEX(ath12k_hw_lock);
> +static struct list_head ath12k_hw_groups = LIST_HEAD_INIT(ath12k_hw_groups);

I can somehow understand/guess why this mutex is needed (even though
there's no documentation) but the naming is not really clear as we
already have struct ath12k_hw::hw_mutex.

> +/* Holds info on the group of devices that are registered as a single wiphy */
> +struct ath12k_hw_group {
> +	struct list_head list;
> +	u8 id;
> +	u8 num_devices;
> +	u8 num_probed;
> +	struct ath12k_base *ab[ATH12K_MAX_SOCS];
> +	/* To synchronize group create, assign, start, stop */
> +	struct mutex mutex_lock;
> +};

But why we really need this mutex? And does it really justify the extra
complexity it creates?

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