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

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Date:   Mon, 18 Nov 2019 08:03:56 -0700
From:   Jeffrey Hugo <jeffrey.l.hugo@...il.com>
To:     Bjorn Andersson <bjorn.andersson@...aro.org>
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 Sun, Nov 17, 2019 at 7:41 PM Bjorn Andersson
<bjorn.andersson@...aro.org> wrote:
>
> 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.

Ah.  Clearly no one needs more than 64k of memory, err 3 uart ports  :)

>
> > > 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.

Sounds good.

>
> 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
> > >