linux-kernel - Re: [PATCH v2 1/3] serial: core: Store fifo timeout again

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Date: Wed, 17 Apr 2024 11:18:33 +0300 (EEST)
From: Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
To: Michael Pratt <mcpratt@...me>
cc: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>, 
    LKML <linux-kernel@...r.kernel.org>, 
    linux-serial <linux-serial@...r.kernel.org>, 
    Greg Kroah-Hartman <gregkh@...uxfoundation.org>, 
    Jiri Slaby <jirislaby@...nel.org>, 
    Wander Lairson Costa <wander@...hat.com>, 
    Vamshi Gajjela <vamshigajjela@...gle.com>
Subject: Re: [PATCH v2 1/3] serial: core: Store fifo timeout again

On Tue, 16 Apr 2024, Michael Pratt wrote:
> On Tuesday, April 16th, 2024 at 14:58, Andy Shevchenko <andriy.shevchenko@...ux.intel.com> wrote:
> 
> > > + if (port->fifosize > 1)
> > > + port->timeout = uart_fifo_timeout(port);
> > 
> > 
> > else
> > port->timeout = port->frame_time;
> > 
> 
> 
> Consistent with what I said in the other reply, the only reason that
> I have an if statement here, is to avoid doing extra math for devices
> without a fifo, as a specifically calculated timeout value would be useless
> in those cases.

Please benchmark to show this actually matters if want to make this claim. 
Otherwise just do the math always.

> However, if you don't like the 10 ms default timeout, perhaps port->frame_time
> could actually be a more reasonable default value? That is, provided 
> that we have a process 
> for calculating the proper value already in place...

While it would be a step toward the correct direction, you'd still need to 
add the safety there which is already done by uart_fifo_timeout(). So no, 
I don't think there's advantage of using port->frame_time over just 
calling uart_fifo_timeout() and ensuring uart_fifo_timeout() is always 
using at least 1 as the FIFO size when it does the calculations.

-- 
 i.