linux-kernel - Re: [PATCH 2/6] serial: 8250_dw: Avoid unnecessary LCR writes

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Message-ID: <aXPrGqUHtCCpKbcN@smile.fi.intel.com>
Date: Fri, 23 Jan 2026 23:41:46 +0200
From: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To: Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Jiri Slaby <jirislaby@...nel.org>, linux-serial@...r.kernel.org,
	qianfan Zhao <qianfanguijin@....com>,
	Adriana Nicolae <adriana@...sta.com>, linux-kernel@...r.kernel.org,
	"Bandal, Shankar" <shankar.bandal@...el.com>,
	"Murthy, Shanth" <shanth.murthy@...el.com>
Subject: Re: [PATCH 2/6] serial: 8250_dw: Avoid unnecessary LCR writes

On Fri, Jan 23, 2026 at 07:27:35PM +0200, Ilpo Järvinen wrote:
> When DW UART is configured with BUSY flag, LCR writes may not always
> succeed which can make any LCR write complex and very expensive.
> Performing write directly can trigger IRQ and the driver has to perform
> complex and distruptive sequence while retrying the write.
> 
> Therefore, it's better to avoid doing LCR write that would not change
> the value of the LCR register. Add LCR write avoidance code into the
> 8250_dw driver's serial_out functions.

.serial_out() ?

...

> +/*
> + * With BUSY, LCR writes can be very expensive (IRQ + complex retry logic).
> + * If the write would not change the value of the LCR register, skip write

would --> does

skip write --> skip it

> + * entirely.
> + */

-- 
With Best Regards,
Andy Shevchenko