Re: [PATCH] ARM: dts: sun8i-q8-common: enable bluetooth on SDIO Wi-Fi

[Chen-Yu Tsai]

On Mon, Dec 19, 2016 at 10:08 PM, Icenowy Zheng <icenowy@xxxxxxxx> wrote:
>
>
> 19.12.2016, 18:09, "Maxime Ripard" <maxime.ripard@xxxxxxxxxxxxxxxxxx>:
>> On Fri, Dec 16, 2016 at 10:40:00PM +0800, Icenowy Zheng wrote:
>>>  >>  > >  &r_pio {
>>>  >>  > >  wifi_pwrseq_pin_q8: wifi_pwrseq_pin@0 {
>>>  >>  > > - pins = "PL6", "PL7", "PL11";
>>>  >>  > > + pins = "PL6", "PL7", "PL8", "PL11";
>>>  >>  > >  function = "gpio_in";
>>>  >>  > >  bias-pull-up;
>>>  >>  > >  };
>>>  >>  >
>>>  >>  > There's several things wrong here. The first one is that you rely
>>>  >>  > solely on the pinctrl state to maintain a reset line. This is very
>>>  >>  > fragile (especially since the GPIO pinctrl state are likely to go away
>>>  >>  > at some point), but it also means that if your driver wants to recover
>>>  >>  > from that situation at some point, it won't work.
>>>  >>  >
>>>  >>  > The other one is that the bluetooth and wifi chips are two devices in
>>>  >>  > linux, and you assign that pin to the wrong device (wifi).
>>>  >>  >
>>>  >>  > rfkill-gpio is made just for that, so please use it.
>>>  >>
>>>  >>  The GPIO is not for the radio, but for the full Bluetooth part.
>>>  >
>>>  > I know.
>>>  >
>>>  >>  If it's set to 0, then the bluetooth part will reset, and the
>>>  >>  hciattach will fail.
>>>  >
>>>  > Both rfkill-gpio and rfkill-regulator will shutdown when called
>>>  > (either by poking the reset pin or shutting down the regulator), so
>>>  > that definitely seems like an expected behavior to put the device in
>>>  > reset.
>>>  >
>>>  >>  The BSP uses this as a rfkill, and the result is that the bluetooth
>>>  >>  on/off switch do not work properly.
>>>  >
>>>  > Then rfkill needs fixing, but working around it by hoping that the
>>>  > core will probe an entirely different device, and enforcing a default
>>>  > that the rest of the kernel might or might not change is both fragile
>>>  > and wrong.
>>>
>>>  I think a rfkill-gpio here works just like the BSP rfkill...
>>>
>>>  The real problem is that the Realtek UART bluetooth driver is a userspace
>>>  program (a modified hciattach), which is not capable of the GPIO reset...
>>
>> Can't you run rfkill before attaching? What is the problem exactly?
>> It's not in reset for long enough?
>>
>> This seems more and more like an issue in the BT stack you're
>> using. We might consider workarounds in the kernel, but they have to
>> be correct.
>
> One more rfkill interface will be generated for hci0 after hciattach, which can
> be safely toggled block and unblock.
>
> However, if the GPIO is toggled down, the hciattach program will die.
>
> The bluetooth stack I used is fd.o's BlueZ.

I think the bigger issue is that the tty/serial subsystem does not have
power sequencing support. Here we're trying to use rfkill to do that,
but that doesn't seem to be what it was intended for. It might work with
standalone USB bluetooth controllers that don't need any special setup,
since the device will just appear and get registered. But it might not
work so well with UART based adapters that need userspace fiddling with
firmware and hciattach.

And like Icenowy mentioned, the bluetooth stack registers another rfkill
control, which presumable just blocks transmissions.

Regards
ChenYu

>
>>
>> Maxime
>>
>> --
>> Maxime Ripard, Free Electrons
>> Embedded Linux and Kernel engineering
>> http://free-electrons.com