linux-kernel - Re: [PATCH v3 06/11] serial: sc16is7xx: fix bug when first setting GPIO direction

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Message-ID: <ZG9CIww5WbgJ3TUf@surfacebook>
Date:   Thu, 25 May 2023 14:10:27 +0300
From:   andy.shevchenko@...il.com
To:     Hugo Villeneuve <hugo@...ovil.com>
Cc:     gregkh@...uxfoundation.org, robh+dt@...nel.org,
        krzysztof.kozlowski+dt@...aro.org, conor+dt@...nel.org,
        jirislaby@...nel.org, jringle@...dpoint.com,
        tomasz.mon@...lingroup.com, l.perczak@...lintechnologies.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>
Subject: Re: [PATCH v3 06/11] serial: sc16is7xx: fix bug when first setting
 GPIO direction

Thu, May 25, 2023 at 12:03:20AM -0400, Hugo Villeneuve kirjoitti:
> From: Hugo Villeneuve <hvilleneuve@...onoff.com>
> 
> When we want to configure a pin as an output pin with a value of logic
> 0, we end up as having a value of logic 1 on the output pin. Setting a
> logic 0 a second time (or more) after that will correctly output a
> logic 0 on the output pin.
> 
> By default, all GPIO pins are configured as inputs. When we enter
> c16is7xx_gpio_direction_output() for the first time, we first set the

Missing 's'.

> desired value in IOSTATE, and then we configure the pin as an output.
> The datasheet states that writing to IOSTATE register will trigger a
> transfer of the value to the I/O pin configured as output, so if the
> pin is configured as an input, nothing will be transferred.
> 
> Therefore, set the direction first in IODIR, and then set the desired
> value in IOSTATE.
> 
> This is what is done in NXP application note AN10587.

-- 
With Best Regards,
Andy Shevchenko