linux-kernel - Re: [PATCH v5 2/3] dt-bindings: net: bluetooth: Add qualcomm-bluetooth

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Date:   Tue, 27 Mar 2018 11:47:22 -0700
From:   Bjorn Andersson <bjorn.andersson@...aro.org>
To:     Thierry Escande <thierry.escande@...aro.org>
Cc:     Marcel Holtmann <marcel@...tmann.org>,
        Rob Herring <robh+dt@...nel.org>,
        Andy Gross <andy.gross@...aro.org>,
        Johan Hedberg <johan.hedberg@...il.com>,
        David Brown <david.brown@...aro.org>,
        Mark Rutland <mark.rutland@....com>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Loic Poulain <loic.poulain@...aro.org>,
        Srinivas Kandagatla <srinivas.kandagatla@...aro.org>,
        linux-bluetooth@...r.kernel.org, linux-arm-msm@...r.kernel.org,
        devicetree <devicetree@...r.kernel.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v5 2/3] dt-bindings: net: bluetooth: Add
 qualcomm-bluetooth

On Tue 27 Mar 08:56 PDT 2018, Thierry Escande wrote:

> Hi Bjorn,
> 
> On 27/03/2018 00:51, Bjorn Andersson wrote:
> > On Tue 20 Mar 23:58 HKT 2018, Marcel Holtmann wrote:
> > > > Signed-off-by: Thierry Escande <thierry.escande@...aro.org>
> > [..]
> > > > + - clocks: clock phandle for SUSCLK_32KHZ
> > > 
> > > if I compare this with broadcom-bluetooth.txt or ti-bluetooth.txt then
> > > besides compatible, everything else is optional. The
> > > nokia-bluetooth.txt has everything required, but that is also a really
> > > specific platform.
> > > 
> > > Can we be less restrictive for a QCA general purpose chip?
> > > 
> > 
> > The way we deal with this in other bindings is that we tie such
> > requirements to the compatible; i.e. we would say that qcom,qca6174-bt
> > requires a clock and we would have something like qcom,qca-bt that makes
> > it optional.
> > 
> > The beauty of this is that the driver will tell you if you forgot to
> > specify the clock when it actually is required, which saves you
> > considerable amount of debugging time.
> > 
> > 
> > NB. The way the bcm driver handles this is insufficient, as it treats
> > any error from clk_get as "there's no clock specified". The driver
> > should accept a clock not being specified, but should fail properly when
> > a clock is specified but can't be acquired (e.g. due to clk_get()
> > returning EPROBE_DEFER).
> > 
> > > > +
> > > > +Example:
> > > > +
> > > > +serial@...0000 {
> > > > +	pinctrl-names = "default", "sleep";
> > > > +	pinctrl-0 = <&blsp1_uart1_default>;
> > > > +	pinctrl-1 = <&blsp1_uart1_sleep>;
> > > > +
> > > > +	bluetooth {
> > > > +		compatible = "qcom,qca6174-bt";
> > > > +
> > > > +		enable-gpios = <&pm8994_gpios 19 GPIO_ACTIVE_HIGH>;
> > > > +
> > > > +		pinctrl-names = "default";
> > > > +		pinctrl-0 = <&bt_en_pin_a>;
> > > 
> > > This one I do not understand and you might want to shed some light
> > > into why this is done that way.
> > > 
> > 
> > This is completely generic and only relates to getting the electrical
> > properties of the gpio pin set up correctly. So I would recommend that
> > we omit this from the binding and example (including the pinctrl
> > properties for the serial above).
> 
> If I remove the pinctrl entry in the bluetooth node, the gpio19 is then
> marked as unclaimed. The drive strength also defaults to low but that
> doesn't seem to be an issue and the the chip can still be enabled through
> gpio19. Is it ok to have it unclaimed? If so I can remove it from the
> binding and the doc then.
> 
> Regarding the blsp1_uart1_default of the serial node, I can still enable the
> chip if I remove it but the hci commands all end in timeout. It seems that
> the function for these pins has to be explicitly set to blsp_uart2. So at
> least, the default pinctrl seems mandatory.
> 

Our board needs these properties to get the uart and gpio in the right
state, but this is unrelated to BT - that's why I suggested that you
omit these properties from the BT binding.

Regards,
Bjorn