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

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Message-ID: <20161216124748.rkvnnlo4x5onzpvk@lukather>
Date:   Fri, 16 Dec 2016 13:47:48 +0100
From:   Maxime Ripard <maxime.ripard@...e-electrons.com>
To:     Icenowy Zheng <icenowy@...c.xyz>
Cc:     Hans de Goede <hdegoede@...hat.com>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        linux-arm-kernel@...ts.infradead.org, devicetree@...r.kernel.org,
        Chen-Yu Tsai <wens@...e.org>
Subject: Re: [PATCH] ARM: dts: sun8i-q8-common: enable bluetooth on SDIO Wi-Fi

On Fri, Dec 09, 2016 at 07:49:00PM +0800, Icenowy Zheng wrote:
> 
> 2016年12月9日 下午4:07于 Maxime Ripard <maxime.ripard@...e-electrons.com>写道：
> >
> > On Tue, Dec 06, 2016 at 04:08:38PM +0800, Icenowy Zheng wrote: 
> > > Some SDIO Wi-Fi chips (such as RTL8703AS) have a UART bluetooth, which 
> > > has a dedicated enable pin (PL8 in the reference design). 
> > > 
> > > Enable the pin in the same way as the WLAN enable pins. 
> > > 
> > > Tested on an A33 Q8 tablet with RTL8703AS. 
> > > 
> > > Signed-off-by: Icenowy Zheng <icenowy@...c.xyz> 
> > > --- 
> > > 
> > > This patch should be coupled with the uart1 node patch I send before: 
> > > http://lists.infradead.org/pipermail/linux-arm-kernel/2016-December/471997.html 
> > > 
> > > For RTL8703AS, the rtl8723bs bluetooth code is used, which can be retrieve from: 
> > > https://github.com/lwfinger/rtl8723bs_bt 
> > > 
> > >  arch/arm/boot/dts/sun8i-q8-common.dtsi | 2 +- 
> > >  1 file changed, 1 insertion(+), 1 deletion(-) 
> > > 
> > > diff --git a/arch/arm/boot/dts/sun8i-q8-common.dtsi b/arch/arm/boot/dts/sun8i-q8-common.dtsi 
> > > index c676940..4aeb5bb 100644 
> > > --- a/arch/arm/boot/dts/sun8i-q8-common.dtsi 
> > > +++ b/arch/arm/boot/dts/sun8i-q8-common.dtsi 
> > > @@ -88,7 +88,7 @@ 
> > >  
> > >  &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.

Maxime

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

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