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Date:   Fri, 1 Dec 2023 10:31:26 -0600
From:   Nishanth Menon <nm@ti.com>
To:     Arnd Bergmann <arnd@arndb.de>
CC:     Tony Lindgren <tony@atomide.com>,
        Francesco Dolcini <francesco@dolcini.it>,
        <linux-arm-kernel@lists.infradead.org>,
        <linux-kernel@vger.kernel.org>,
        Vignesh Raghavendra <vigneshr@ti.com>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Will Deacon <will@kernel.org>, Tero Kristo <kristo@kernel.org>
Subject: Re: [PATCH] arm64: defconfig: increase SERIAL_8250_NR_UARTS
Message-ID: <20231201163126.oaixjeo4i3gvmsyt@molar>
References: <20231130231657.12715-1-francesco@dolcini.it>
 <20231201060346.GE5169@atomide.com>
 <20231201064919.5mbmqo5fco7n3rgq@endnote>
 <855dfa50-a3a3-415a-8612-4da59f995ef0@app.fastmail.com>
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On 16:31-20231201, Arnd Bergmann wrote:
> On Fri, Dec 1, 2023, at 07:49, Nishanth Menon wrote:
> > On 08:03-20231201, Tony Lindgren wrote:
> >> * Francesco Dolcini <francesco@dolcini.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.
> >> 
> >> OK makes sense for distro use.
> >> 
> >> Disabling unused ports leads into port names shifting, which we still can't
> >> easily tolerate until we have the DEVNAME:0.0 style addressing available for
> >> ports. So for now we still depend CONFIG_SERIAL_8250_NR_UARTS, eventually
> >> that too should become just a legacy ISA port array.. Meanwhile:
> >> 
> >> Reviewed-by: Tony Lindgren <tony@atomide.com>
> >
> > 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 8250 debate has been
> > popping on and off over the years.. Sigh.. memories of [1] still haunt
> > me.
> 
> I don't recall any reason to have the limit set to the default
> of 4, other than possibly using excessive amounts of .data in
> vmlinux, but we have other serial port drivers that just hardcode
> a much larger value.

Thanks Arnd, we will queue this up.

Francesco: Could you respin with a more clear commit message to indicate
actual board usage instance.

-- 
Regards,
Nishanth Menon
Key (0xDDB5849D1736249D) / Fingerprint: F8A2 8693 54EB 8232 17A3  1A34 DDB5 849D 1736 249D