linux-kernel - Re: [PATCH] arm64: dts: qcom: msm8998-mtp: Add alias for blsp1

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Message-ID: <20191118024145.GC25371@yoga>
Date:   Sun, 17 Nov 2019 18:41:45 -0800
From:   Bjorn Andersson <bjorn.andersson@...aro.org>
To:     Jeffrey Hugo <jeffrey.l.hugo@...il.com>
Cc:     Andy Gross <agross@...nel.org>,
        MSM <linux-arm-msm@...r.kernel.org>,
        DTML <devicetree@...r.kernel.org>,
        lkml <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] arm64: dts: qcom: msm8998-mtp: Add alias for blsp1_uart3

On Sat 16 Nov 14:24 PST 2019, Jeffrey Hugo wrote:

> On Fri, Nov 15, 2019 at 11:44 PM Bjorn Andersson
> <bjorn.andersson@...aro.org> wrote:
> >
> > The msm_serial driver uses a simple counter to determine which port to
> > use when no alias is defined, but there's no logic to prevent this from
> 
> Which port to use for what, the default console?
> 

The driver defines three (3) struct uart_ports (wrapped in struct
msm_ports), see msm_uart_port[] around line 1538 in msm_serial.c

This means that you can have a whooping 3 instances of msm_serial in the
system and per the logic found in msm_serial_probe() the allocation
follows the serial%d aliases defined and for entries without an alias a
simple counter, starting at 0 is used.

> > not colliding with what's defined by the aliases. As a result either
> > none or all of the active msm_serial instances must be listed as
> > aliases.
> >
> > Define blsp1_uart3 as "serial1" to mitigate this problem.
> >
> > Fixes: 4cffb9f2c700 ("arm64: dts: qcom: msm8998-mtp: Enable bluetooth")
> > Signed-off-by: Bjorn Andersson <bjorn.andersson@...aro.org>
> 
> That driver behavior seems like a strange thing to be doing.
> 
> If you clarify the question above, -
> Reviewed-by: Jeffrey Hugo <jeffrey.l.hugo@...il.com>
> 

Thanks, I'll respin the message to properly document this behavior.

Regards,
Bjorn

> > ---
> >  arch/arm64/boot/dts/qcom/msm8998-mtp.dtsi | 1 +
> >  1 file changed, 1 insertion(+)
> >
> > diff --git a/arch/arm64/boot/dts/qcom/msm8998-mtp.dtsi b/arch/arm64/boot/dts/qcom/msm8998-mtp.dtsi
> > index 5f101a20a20a..e08fcb426bbf 100644
> > --- a/arch/arm64/boot/dts/qcom/msm8998-mtp.dtsi
> > +++ b/arch/arm64/boot/dts/qcom/msm8998-mtp.dtsi
> > @@ -9,6 +9,7 @@
> >  / {
> >         aliases {
> >                 serial0 = &blsp2_uart1;
> > +               serial1 = &blsp1_uart3;
> >         };
> >
> >         chosen {
> > --
> > 2.23.0
> >