linux-kernel - Re: [PATCH v2 3/3] serial: 8250: Set fifo timeout using uart_fifo

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Message-ID: <CmMdmgjPFh8R-rH0-mjU0QdQcqhRwVr9bmApDJ7BV_9DjRBL35K_Qfjs7oIPVwGFv5mdT476a8tPtkgnWqY2lRBEfGvfhjk0yW9ueI4bcf8=@pm.me>
Date: Tue, 16 Apr 2024 19:15:03 +0000
From: Michael Pratt <mcpratt@...me>
To: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc: linux-kernel@...r.kernel.org, linux-serial@...r.kernel.org, Greg Kroah-Hartman <gregkh@...uxfoundation.org>, Jiri Slaby <jirislaby@...nel.org>, Wander Lairson Costa <wander@...hat.com>, Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>, Vamshi Gajjela <vamshigajjela@...gle.com>
Subject: Re: [PATCH v2 3/3] serial: 8250: Set fifo timeout using uart_fifo_timeout()

Hi Andy,

On Tuesday, April 16th, 2024 at 14:57, Andy Shevchenko <andriy.shevchenko@...ux.intel.com> wrote:

> 
> > unsigned int status, tmout = 10000;
> > 
> > - /* Wait up to 10ms for the character(s) to be sent. /
> > + / Wait for a time relative to buffer size and baud */
> > + if (up->fifo_enable && up->port.timeout)
> > + tmout = jiffies_to_usecs(up->port.timeout);
> 
> 
> Why do we still use that default? Can't we calculate timeout even for\
> FIFO-less / FIFO-disabled devices?

Maybe it's possible that there is some kind of rare case where the LSR register
is not working or not configured properly for a device in which support
is being worked on...without a timeout, that would result in an infinite loop.

AFAIK, when everything is working properly, there is no such thing as needing
a timeout for a uart device without fifo, as every single byte written would trigger
an interrupt anyway.

> --
> With Best Regards,
> Andy Shevchenko

--
MCP