diff mbox series

[v9,09/10] serial: sc16is7xx: add post reset delay

Message ID 20230725142343.1724130-10-hugo@hugovil.com
State New
Headers
Series serial: sc16is7xx: fix GPIO regression and rs485 improvements |

Commit Message

Hugo Villeneuve July 25, 2023, 2:23 p.m. UTC 
  From: Hugo Villeneuve <hvilleneuve@dimonoff.com>

Make sure we wait at least 3us before initiating communication with
the device after reset.

Signed-off-by: Hugo Villeneuve <hvilleneuve@dimonoff.com>
Reviewed-by: Lech Perczak <lech.perczak@camlingroup.com>
Tested-by: Lech Perczak <lech.perczak@camlingroup.com>
---
 drivers/tty/serial/sc16is7xx.c | 6 ++++++
 1 file changed, 6 insertions(+)

Comments

Greg KH July 31, 2023, 3:57 p.m. UTC | #1 
On Tue, Jul 25, 2023 at 10:23:41AM -0400, Hugo Villeneuve wrote:
> From: Hugo Villeneuve <hvilleneuve@dimonoff.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?

Please read the kernel documentation again for how to write a good
changelog text.  It's usually the hardest part of submitting a patch.

> 
> Signed-off-by: Hugo Villeneuve <hvilleneuve@dimonoff.com>
> Reviewed-by: Lech Perczak <lech.perczak@camlingroup.com>
> Tested-by: Lech Perczak <lech.perczak@camlingroup.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.

:(
Hugo Villeneuve July 31, 2023, 5 p.m. UTC | #2 
On Mon, 31 Jul 2023 17:57:50 +0200
Greg KH <gregkh@linuxfoundation.org> wrote:

> On Tue, Jul 25, 2023 at 10:23:41AM -0400, Hugo Villeneuve wrote:
> > From: Hugo Villeneuve <hvilleneuve@dimonoff.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@dimonoff.com>
> > Reviewed-by: Lech Perczak <lech.perczak@camlingroup.com>
> > Tested-by: Lech Perczak <lech.perczak@camlingroup.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.
diff mbox series

Patch

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);
+
 	for (i = 0; i < devtype->nr_uart; ++i) {
 		s->p[i].line		= i;
 		/* Initialize port data */