linux-kernel - Re: [PATCH v9 09/10] serial: sc16is7xx: add post reset delay

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Date:   Mon, 31 Jul 2023 17:57:50 +0200
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Hugo Villeneuve <hugo@...ovil.com>
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>
Subject: Re: [PATCH v9 09/10] serial: sc16is7xx: add post reset delay

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?

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@...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.

:(