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Date:   Fri, 1 Dec 2023 13:19:58 -0600
From:   Nishanth Menon <nm@ti.com>
To:     Francesco Dolcini <francesco@dolcini.it>
CC:     <linux-arm-kernel@lists.infradead.org>,
        <linux-kernel@vger.kernel.org>, Arnd Bergmann <arnd@arndb.de>,
        Vignesh Raghavendra <vigneshr@ti.com>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Will Deacon <will@kernel.org>, Tero Kristo <kristo@kernel.org>,
        Tony Lindgren <tony@atomide.com>
Subject: Re: [PATCH v2] arm64: defconfig: increase SERIAL_8250_NR_UARTS
Message-ID: <20231201191958.kmwkpmttmebsas47@kooky>
References: <20231201171544.1901-1-francesco@dolcini.it>
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In-Reply-To: <20231201171544.1901-1-francesco@dolcini.it>
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On 18:15-20231201, Francesco Dolcini wrote:
> 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").
> 
> The need to increase this value was noticed while working with Toradex
> Verdin AM62, this board has 4 serial UART instances available to the user
> plus an internal one that is connected to a Bluetooth module. Without this
> change the fifth UART connected to the BT module is not instantiated and BT
> is not working.
> 
> Instead of increasing the number to the bare minimum (5) that would be
> required to solve this specific issue, we increase this to 8 which seems a
> more reasonable number to have in the defconfig and should cover more valid
> use cases.

To address Arnd's concern on size increase, it will be good to add:
---
With this change kernel image increases by ~3.2k. bloat-o-meter summary:
add/remove: 1/1 grow/shrink: 7/0 up/down: 3220/-8 (3212)
---

Full bloat-o-meter report: aarch64-none-linux-gnu-gcc (11.3.1 20220712)
$ ./scripts/bloat-o-meter ./vmlinux.old vmlinux
add/remove: 1/1 grow/shrink: 7/0 up/down: 3220/-8 (3212)
Function                                     old     new   delta
serial8250_ports                            3136    6272   +3136
serial8250_register_8250_port               1176    1208     +32
serial8250_remove                            120     136     +16
serial8250_unregister_port                   288     296      +8
serial8250_suspend                           120     128      +8
serial8250_setup_port                        212     220      +8
e843419@0d28_000102dd_3a64                     -       8      +8
serial8250_init                              468     472      +4
e843419@0c0a_0000eb9e_8cc                      8       -      -8
Total: Before=28756614, After=28759826, chg +0.01%

> 
> Cc: Tony Lindgren <tony@atomide.com>
> Reviewed-by: Tony Lindgren <tony@atomide.com>
> Signed-off-by: Francesco Dolcini <francesco@dolcini.it>
> ---
>  arch/arm64/configs/defconfig | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/arch/arm64/configs/defconfig b/arch/arm64/configs/defconfig
> index b60aa1f89343..ecd365cd1d87 100644
> --- a/arch/arm64/configs/defconfig
> +++ b/arch/arm64/configs/defconfig
> @@ -448,6 +448,7 @@ CONFIG_SERIO_AMBAKMI=y
>  CONFIG_LEGACY_PTY_COUNT=16
>  CONFIG_SERIAL_8250=y
>  CONFIG_SERIAL_8250_CONSOLE=y
> +CONFIG_SERIAL_8250_NR_UARTS=8
>  CONFIG_SERIAL_8250_EXTENDED=y
>  CONFIG_SERIAL_8250_SHARE_IRQ=y
>  CONFIG_SERIAL_8250_BCM2835AUX=y
> -- 
> 2.39.2
> 

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