netdev - Re: [PATCH v2] Bluetooth: Add LED triggers for HCI frames tx and rx

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Message-Id: <30869CE7-FE5E-4CAF-86FC-D140E2C0963D@holtmann.org>
Date:	Tue, 16 Aug 2016 14:33:13 +0200
From:	Marcel Holtmann <marcel@...tmann.org>
To:	Guodong Xu <guodong.xu@...aro.org>
Cc:	"Gustavo F. Padovan" <gustavo@...ovan.org>,
	Johan Hedberg <johan.hedberg@...il.com>,
	"David S. Miller" <davem@...emloft.net>,
	"open list:BLUETOOTH DRIVERS" <linux-bluetooth@...r.kernel.org>,
	Network Development <netdev@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH v2] Bluetooth: Add LED triggers for HCI frames tx and rx

Hi Guodong,

>>> Two LED triggers are added into hci_dev: tx_led and rx_led. Upon ACL/SCO
>>> packets available in tx or rx, the LEDs will blink.
>>> 
>>> For each hci registration, two triggers are added into LED subsystem:
>>> [hdev->name]-tx and [hdev-name]-rx.
>>> Refer to Documentation/leds/leds-class.txt for usage.
>>> 
>>> Verified on HiKey 96boards, which uses HiSilicon hi6220 SoC and TI
>>> WL1835 WiFi/BT combo chip.
>> 
>> so I have no idea what to do with adding adding hci0-rx and hci0-tx triggers. Combined with hci0-power trigger these are already 3 triggers. And if you have 2 Bluetooth controllers in your system, then you have 6 triggers.
>> 
> 
> True, 6 triggers. But, taking example for other subsytems, eg. cpu
> cores. On my board, I have "heartbeat cpu0 cpu1 cpu2 cpu3 cpu4 cpu5
> cpu6 cpu7". It doesn't have to mean you need all of them connected to
> some LED(s). Actually, in most of the case, I only need heartbeat.
> 
> 
> 
>> If we then maybe add another trigger, then this number just goes up and up.
>> 
>> As far as I can tell you can only assign a single trigger to a LED.
>> 
> 
> That's true. And people got a choice of which feature he wants to visualize.

and as a result we keep adding senseless triggers to the kernel and bloating it up for no reason. Especially since it feels like 99% of the LED triggers are not used at all. This makes no sense to me.

>> So this means to even use these triggers, you need now 3 LEDs per Bluetooth controller. How is that useful for anybody in a real system? Maybe I am missing something here and somehow there is magic to combine triggers, but I have not found it yet. So please someone enlighten me on how this is suppose to be used with real devices.
>> 
>> Recently I have added a simple bluetooth-power trigger that combines all Bluetooth controllers into a single trigger. If any of them is enabled, then you can control your LED. Which makes a lot more sense to me since you most likely have a single Bluetooth LED on your system. And you want it to show the correct state no matter what Bluetooth controller is in use. However I can see the case that someone might want to assign one specific Bluetooth controller to a LED status.
>> 
>> So instead of adding many independent triggers to each controller, why not create one global bluetooth trigger and one individual bluetooth-hci0 trigger for each controller. And the combine power, tx, rx and whatever else we need to trigger the LED for?
>> 
> 
> When I starting this work, I referred to WiFi system. See
> CONFIG_MAC80211_LEDS. WiFi system implements these types of triggers "
> phy0rx phy0tx phy0assoc phy0radio" for each 'controller'.

And I actually wonder who ever used these triggers. You need 4 LEDs to visualize the WiFi status. Which systems has 4 LEDs to spare to visualize this.

> Besides, there are also RFKILL which stands for WiFi/BT power status.
> RFKILL adds triggers for each module too. Eg. in the below example, I
> have one WiFi (phy0), one BT (hci0). Trigger rfkill1 equals to
> hci0-power.
> 
> Ref: here are all LED triggers I found in my 96boards/HiKey:
> 
> # cat trigger
> none kbd-scrollock kbd-numlock kbd-capslock kbd-kanalock kbd-shiftlock
> kbd-altgrlock kbd-ctrllock kbd-altlock kbd-shiftllock kbd-shiftrlock
> kbd-ctrlllock kbd-ctrlrlock mmc0 mmc1 heartbeat cpu0 cpu1 cpu2 cpu3
> cpu4 cpu5 cpu6 cpu7 mmc2 rfkill0 phy0rx phy0tx phy0assoc phy0radio
> hci0-power hci0-tx [hci0-rx] rfkill1

And how many LEDs do you have in the your system? I think you are making my point here.

So I think what we need to do is to not add to this madness and instead create one "bluetooth" LED trigger that combines power and TX/RX for all controllers. And then allow for individual "bluetooth-hci0" LED triggers so that you can bind a single Bluetooth controller to a single LED.

For me, if I can not combine hci0-power, hci0-tx and hci0-rx into a single LED, it becomes utterly useless on pretty much every system that is out there.

Regards

Marcel