Re: [PATCH v4 2/3] dt-bindings: net: bluetooth: Add qualcomm-bluetooth

[Thierry Escande]

Hi Marcel,

On 14/03/2018 20:51, Marcel Holtmann wrote:
> Hi Bjorn,
>
> > > > > > +		bt-disable-n-gpios = <&pm8994_gpios 19 GPIO_ACTIVE_HIGH>;
> > > > >
> > > > > can we use a common name here. I think that Nokia and Broadcom drivers
> > > > > define one. And if this is the enable/shutdown GPIO, we should name it
> > > > > consistently across all manufacturers. It essentially does the same on
> > > > > Bluetooth UART chips no matter what chip is behind them.
> > > >
> > > > Broadcomm has a device-wakup-gpios and Nokia has bluetooth-wakup-gpios.
> > > > It might be that these behave in the same way, but from the description
> > > > they only trigger the wakeup.
> > >
> > > that is something that we might need to start fixing. I really prefer
> > > if we name the GPIOs a bit more consistent.
> > >
> > > > The reason for the proposed naming here is that the pin is named
> > > > "BT_DISABLE_N" in the datasheet.
> > >
> > > That is not a reason I buy. So the next board comes around that labels
> > > it in the data sheet BT_DISABLE_YEAH_SUPER_GREAT and you send me a
> > > patch to the driver to look for that name. If the GPIO does the same
> > > thing, I couldnât care less what the data sheet says. That might be
> > > a comment in the DT file, but it should not pollute the driver code.
> >
> > BT_DISABLE_N is the name of this pin in the datasheet of the QCA chip,
> > not on the board, so this name is the same regardless of what you name
> > the line or gpio your board connect it to.
>
> and QCA chip v1 and QCA chip v2 will use the same driver and same firmware loading mechanism. So why do we have to add a new GPIO naming if they decide to change the name in the data sheet. With Bluetooth it is pretty much all the same. Every UART chip has a shutdown/reset GPIO to enable/disable the chip behind the UART.
>
> > > A new board should not require driver changes, you just ship a new DT
> > > for that board and an existing driver hopefully just does the job. No
> > > matter how someone named a GPIO in a piece of paper.
> >
> > I totally agree with the fact that the board should not affect the
> > naming of the gpio in the driver. But I do enjoy when we refer to pins
> > by their real name - instead of having to guess which pin in the _chip_
> > specification the driver actually refer to.
> >
> >
> > That said, what name would you prefer for this?
> >
> > Afaict this is not "wakeup" and there are a few extra steps between the
> > disabled state and "bluetooth is enabled", so "enable" feels slightly
> > wrong. And it probably should be "bluetooth" and not just "device" as
> > this refers to a pin on a WiFi/BT combo chip.
>
> The Broadcom side called it shutdown GPIO, it is essentially the shutdown/reset GPIO or power on/off GPIO. Personally I do not care what it is named, but it will be all the same for all Bluetooth chips. Take a poll from Broadcom, Intel, Realtek and Qualcomm and you can pick a reasonable common name.

The Nokia driver has "bluetooth-wakeup" gpio. The Broadcom one has 
"device-wakeup" and "shutdown". The "shutdown" gpio is set to its active 
state to power on the chip which sounds reversed logic. Same for the 
"bt-disable-n" gpio in the Qualcomm driver, configured as ACTIVE_HIGH, 
and which is set to 1 to enable it...

So for consistency, naming it as "shutdown" to stick to the bcm driver 
but it should be configured as ACTIVE_LOW in the dts so we actually do a 
gpiod_set_value(0) to un-shutdown it. Does that sound ok?

Regards,
Thierry

> For the wakeup GPIOs, these are different and depend on if there is some low-power mode provided. You would need to check the data sheet to see if they provide more advanced low-power state handling.
>
> Regards
>
> Marcel