From: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
To: "Ilpo Järvinen" <ilpo.jarvinen@linux.intel.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
Jiri Slaby <jirislaby@kernel.org>,
linux-serial@vger.kernel.org,
qianfan Zhao <qianfanguijin@163.com>,
Adriana Nicolae <adriana@arista.com>,
linux-kernel@vger.kernel.org, "Bandal,
Shankar" <shankar.bandal@intel.com>,
"Murthy, Shanth" <shanth.murthy@intel.com>
Subject: Re: [PATCH 2/6] serial: 8250_dw: Avoid unnecessary LCR writes
Date: Fri, 23 Jan 2026 23:41:46 +0200 [thread overview]
Message-ID: <aXPrGqUHtCCpKbcN@smile.fi.intel.com> (raw)
In-Reply-To: <20260123172739.13410-3-ilpo.jarvinen@linux.intel.com>
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
next prev parent reply other threads:[~2026-01-23 21:41 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-01-23 17:27 [PATCH 0/6] 8250 DW UART fixes when under constant Rx pressure Ilpo Järvinen
2026-01-23 17:27 ` [PATCH 1/6] serial: 8250: Protect LCR write in shutdown Ilpo Järvinen
2026-01-23 17:27 ` [PATCH 2/6] serial: 8250_dw: Avoid unnecessary LCR writes Ilpo Järvinen
2026-01-23 21:41 ` Andy Shevchenko [this message]
2026-01-23 17:27 ` [PATCH 3/6] serial: 8250_dw: Rework dw8250_handle_irq() locking and IIR handling Ilpo Järvinen
2026-01-23 22:05 ` Andy Shevchenko
2026-01-27 12:48 ` Ilpo Järvinen
2026-01-27 13:48 ` Andy Shevchenko
2026-01-23 17:27 ` [PATCH 4/6] serial: 8250_dw: Rework IIR_NO_INT handling to stop interrupt storm Ilpo Järvinen
2026-01-23 22:13 ` Andy Shevchenko
2026-01-27 13:01 ` Ilpo Järvinen
2026-01-27 13:57 ` Andy Shevchenko
2026-01-23 17:27 ` [PATCH 5/6] serial: 8250: Add late synchronize_irq() to shutdown to handle DW UART BUSY Ilpo Järvinen
2026-01-23 17:27 ` [PATCH 6/6] serial: 8250_dw: Ensure BUSY is deasserted Ilpo Järvinen
2026-01-23 22:42 ` Andy Shevchenko
2026-01-27 13:35 ` Ilpo Järvinen
2026-01-27 14:10 ` Andy Shevchenko
2026-01-27 14:40 ` Ilpo Järvinen
2026-01-27 16:19 ` John Ogness
2026-01-26 15:22 ` Greg Kroah-Hartman
2026-01-27 14:45 ` Ilpo Järvinen
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