linux-kernel - Re: [PATCH] arm64: defconfig: increase SERIAL_8250_NR

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Message-ID: <ZWmk/t7wPJW71emR@francesco-nb.int.toradex.com>
Date:   Fri, 1 Dec 2023 10:18:54 +0100
From:   Francesco Dolcini <francesco@...cini.it>
To:     Nishanth Menon <nm@...com>
Cc:     Francesco Dolcini <francesco@...cini.it>,
        Tony Lindgren <tony@...mide.com>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Arnd Bergmann <arnd@...db.de>,
        Vignesh Raghavendra <vigneshr@...com>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>, Tero Kristo <kristo@...nel.org>
Subject: Re: [PATCH] arm64: defconfig: increase SERIAL_8250_NR_UARTS

On Fri, Dec 01, 2023 at 02:59:57AM -0600, Nishanth Menon wrote:
> On 09:48-20231201, Francesco Dolcini wrote:
> > On Fri, Dec 01, 2023 at 12:49:19AM -0600, Nishanth Menon wrote:
> > > On 08:03-20231201, Tony Lindgren wrote:
> > > > * Francesco Dolcini <francesco@...cini.it> [231130 23:17]:
> > > > > Increase CONFIG_SERIAL_8250_NR_UARTS from 4 to 8, the current legacy value
> > > > > is not adequate for embedded systems that use SoCs where it's common to
> > > > > have a large number of serial ports.
> > > > > 
> > > > > No need to change CONFIG_SERIAL_8250_RUNTIME_UARTS, see commit 9d86719f8769
> > > > > ("serial: 8250: Allow using ports higher than SERIAL_8250_RUNTIME_UARTS").
> > > > > 
> > > > > This enables using the UART connected Bluetooth device on Verdin AM62
> > > > > board.
> > > 
> > > I'd prefer to get Arnd's view on the topic as well (I kind of
> > > recollect some historic discussion which I am not failing to trace
> > > that there usage model doesn't exceed 4 and aliases could be used to
> > > map these as required for the platform).
> > 
> > The usage model that triggered this change exceed 4, we >4 uart in
> > use at the same time.
> > 
> > And the issue is not really "distro use", and I do not think anything
> > about aliases matter (the BT device is described as a child of the uart
> > in the DT).
> > 
> >   &main_uart5 {
> >     bluetooth {
> >       compatible = "nxp,88w8987-bt";
> >     };
> >   };
> > 
> > The change here is required to have basic hardware functionalities
> > working for kernel development and debugging using the in-tree
> > defconfig.
> 
> I'd suggest to elaborate on "This enables using the UART connected
> Bluetooth device on Verdin AM62 board."

I can do this, of course, I'll wait for some more feedback in the coming
days as you somehow already suggested.

Francesco