[linux-sunxi] Re: [PATCH 7/7] ARM: sun7i: cubietruck: enable bluetooth module

From: arend@broadcom•com (Arend van Spriel)
To: linux-arm-kernel@lists•infradead.org
Subject: [linux-sunxi] Re: [PATCH 7/7] ARM: sun7i: cubietruck: enable bluetooth module
Date: Thu, 17 Apr 2014 09:43:40 +0200	[thread overview]
Message-ID: <534F862C.8010604@broadcom.com> (raw)
In-Reply-To: <534E8102.4070404@redhat.com>

+ linux-serial at vger.kernel.org

On 16/04/14 15:09, Hans de Goede wrote:
> Hi,
>
> On 04/16/2014 12:39 PM, Chen-Yu Tsai wrote:
>> Hi,
>>
>> On Wed, Apr 16, 2014 at 5:44 PM, Maxime Ripard
>> <maxime.ripard@free-electrons•com> wrote:
>>> Hi,
>>>
>>> Please try to keep me in CC, even though the ML doesn't make it easy..
>>
>> Sorry about that.
>>
>>> On Wed, Apr 16, 2014 at 12:06:59AM +0800, Chen-Yu Tsai wrote:
>>>>>> @@ -139,4 +152,16 @@
>>>>>>        reg_usb2_vbus: usb2-vbus {
>>>>>>                status = "okay";
>>>>>>        };
>>>>>> +
>>>>>> +     rfkill_bt {
>>>>>> +             compatible = "rfkill-gpio";
>>>>>> +             pinctrl-names = "default";
>>>>>> +             pinctrl-0 = <&bt_pwr_pin_cubietruck>, <&clk_out_a_pins_a>;
>>>>>> +             clocks = <&clk_out_a>;
>>>>>> +             clock-frequency = <32768>;
>>>>>> +             gpios = <&pio 7 18 0>; /* PH18 */
>>>>>> +             gpio-names = "reset";
>>>>>> +             rfkill-name = "bt";
>>>>>> +             rfkill-type = <2>;
>>>>>> +     };
>>>>>
>>>>> Hmmm, I don't think that's actually right.
>>>>>
>>>>> If you have such a device, then I'd expect it to be represented as a
>>>>> full device in the DT, probably with one part for the WiFi, one part
>>>>> for the Bluetooth, and here the definition of the rfkill device that
>>>>> controls it.
>>>>
>>>> The AP6210 is not one device, but 2 separate chips in one module. Each
>>>> chip has its own controls and interface. They just so happen to share
>>>> the same enclosure. Even 2-in-1 chips by Broadcom have separate controls
>>>> and interfaces. The WiFi side is most likely connected via SDIO, while
>>>> the Bluetooth side is connected to a UART, and optionally I2S for sound.
>>>
>>> It's even easier to represent then.
>>>
>>>>> But tying parts of the device to the rfkill that controls it, such as
>>>>> the clocks, or the frequency it runs at seems just wrong.
>>>>
>>>> I understand where you're coming from. For devices on buses that require
>>>> drivers (such as USB, SDIO) these properties probably should be tied to
>>>> the device node.
>>>>
>>>> For our use case here, which is a bluetooth chip connected on the UART,
>>>> there is no in kernel representation or driver to tie them to. Same goes
>>>> for UART based GPS chips. They just so happen to require toggling a GPIO,
>>>> and maybe enabling a specific clock, to get it running. Afterwards,
>>>> accessing it is done solely from userspace. For our Broadcom chips, the
>>>> user has to upload its firmware first, then designate the tty as a Bluetooth
>>>> HCI using hciattach.
>>>>
>>>> We are using the rfkill device as a on-off switch.
>>>
>>> I understand your point, but the fact that it's implemented in
>>> user-space, or that UART is not a bus (which probably should be), is
>>> only a Linux specific story, and how it's implemented in Linux (even
>>> if the whole rfkill node is another one, but let's stay on topic).
>>
>> I gave it some thought last night. You are right. My whole approach
>> is wrong. But let's try to make it right.
>>
>> So considering the fact that it's primarily connected to a UART,
>> maybe I should make it a sub-node to the UART node it's actually
>> connected to? Something like:
>>
>>          uart2: serial at 01c28800 {
>>                  pinctrl-names = "default";
>>                  pinctrl-0 = <&uart2_pins_a>;
>>                  status = "okay";
>>
>>                  bt: bt_hci {
>>                          compatible = "brcm,bcm20710";
>>                          /* maybe add some generic compatible */
>>                          pinctrl-names = "default";
>>                          pinctrl-0 = <&clk_out_a_pins_a>,
>> <&bt_pwr_pin_cubietruck>;
>>                          clocks = <&clk_out_a>;
>>                          clock-frequency = <32768>;
>>                          gpios = <&pio 7 18 0>; /* PH18 */
>>                  };
>>          };
>>
>> And let the uart core handle power sequencing for sub-nodes.
>
> Great, I missed this reply when I typed my mail I send a few minutes
> ago. I agree that this approach is how thing should be.

Regarding the device tree hierarchy this seems right, but powering the 
sub-nodes seems outside the realm of uart core.

> Regards,
>
> Hans
>
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