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Message-Id: <20230731130059.f098bed0f6a9957fe4444758@hugovil.com>
Date: Mon, 31 Jul 2023 13:00:59 -0400
From: Hugo Villeneuve <hugo@...ovil.com>
To: Greg KH <gregkh@...uxfoundation.org>
Cc: robh+dt@...nel.org, krzysztof.kozlowski+dt@...aro.org,
conor+dt@...nel.org, jirislaby@...nel.org, jringle@...dpoint.com,
isaac.true@...onical.com, jesse.sung@...onical.com,
l.perczak@...lintechnologies.com, tomasz.mon@...lingroup.com,
linux-serial@...r.kernel.org, devicetree@...r.kernel.org,
linux-kernel@...r.kernel.org, linux-gpio@...r.kernel.org,
Hugo Villeneuve <hvilleneuve@...onoff.com>,
Lech Perczak <lech.perczak@...lingroup.com>,
andy.shevchenko@...il.com
Subject: Re: [PATCH v9 09/10] serial: sc16is7xx: add post reset delay
On Mon, 31 Jul 2023 17:57:50 +0200
Greg KH <gregkh@...uxfoundation.org> wrote:
> On Tue, Jul 25, 2023 at 10:23:41AM -0400, Hugo Villeneuve wrote:
> > From: Hugo Villeneuve <hvilleneuve@...onoff.com>
> >
> > Make sure we wait at least 3us before initiating communication with
> > the device after reset.
>
> That says what you do, but not _why_ you do it?
You are right, it is not clear. I will add a note that it is
recommended to do so by the manufacturer in the device datasheet.
> Please read the kernel documentation again for how to write a good
> changelog text. It's usually the hardest part of submitting a patch.
Yes.
> > Signed-off-by: Hugo Villeneuve <hvilleneuve@...onoff.com>
> > Reviewed-by: Lech Perczak <lech.perczak@...lingroup.com>
> > Tested-by: Lech Perczak <lech.perczak@...lingroup.com>
> > ---
> > drivers/tty/serial/sc16is7xx.c | 6 ++++++
> > 1 file changed, 6 insertions(+)
> >
> > diff --git a/drivers/tty/serial/sc16is7xx.c b/drivers/tty/serial/sc16is7xx.c
> > index 49213be60baf..718e982e1efe 100644
> > --- a/drivers/tty/serial/sc16is7xx.c
> > +++ b/drivers/tty/serial/sc16is7xx.c
> > @@ -1526,6 +1526,12 @@ static int sc16is7xx_probe(struct device *dev,
> > regmap_write(s->regmap, SC16IS7XX_IOCONTROL_REG << SC16IS7XX_REG_SHIFT,
> > SC16IS7XX_IOCONTROL_SRESET_BIT);
> >
> > + /*
> > + * After reset, the host must wait at least 3us before initializing a
> > + * communication with the device.
> > + */
> > + usleep_range(5, 10);
>
> 5, 10 is NOT 3us.
In v3, Andy Shevchenko suggested "I would put (5, 10) instead to relax
a bit the scheduler."
Should I add a comment to that effect:
/*
* After reset, the datasheet indicates that the host must wait at least
* 3us before initializing a communication with the device.
* Use (5, 10) range to relax the scheduler.
*/
?
Hugo.
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