linux-kernel - Re: [PATCH V2 1/1] USB: serial: f81232: fix incomplete serial port generation

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Message-ID: <aS2aQF_6ljhFtLI_@hovoldconsulting.com>
Date: Mon, 1 Dec 2025 14:38:08 +0100
From: Johan Hovold <johan@...nel.org>
To: "Ji-Ze Hong (Peter Hong)" <peter_hong@...tek.com.tw>
Cc: gregkh@...uxfoundation.org, linux-usb@...r.kernel.org,
	linux-kernel@...r.kernel.org, tom_tsai@...tek.com.tw,
	yu_chen@...tek.com.tw
Subject: Re: [PATCH V2 1/1] USB: serial: f81232: fix incomplete serial port
 generation

On Fri, Nov 28, 2025 at 04:52:44PM +0800, Ji-Ze Hong (Peter Hong) wrote:
> The Fintek F81532A/534A/535/536 family relies on the
> F81534A_CTRL_CMD_ENABLE_PORT (116h) register during initialization to
> both determine serial port status and control port creation. If the
> driver experiences fast load/unload cycles, the device state may becomes
> unstable, resulting in the incomplete generation of serial ports.
> 
> Performing a dummy read operation on the register prior to the initial
> write command resolves the issue. This clears the device's stale internal
> state. Subsequent write operations will correctly generate all serial
> ports.
> 
> Tested on: HygonDM1SLT(Hygon C86 3250 8-core Processor)
> 
> Signed-off-by: Ji-Ze Hong (Peter Hong) <peter_hong@...tek.com.tw>
> ---
> Changelog:
> v2:
> 	1. remove loop in accessor function.

Thanks for verifying.

Did you try removing the retry loop also in the set_register() helper?
Perhaps that's no longer needed after the dummy read.

Johan