linux-kernel - Re: [PATCH v2] DTS: ARM: gta04: introduce legacy spi-cs-high to make display work again

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Message-ID: <20190923173441.GV5610@atomide.com>
Date:   Mon, 23 Sep 2019 10:34:41 -0700
From:   Tony Lindgren <tony@...mide.com>
To:     "H. Nikolaus Schaller" <hns@...delico.com>
Cc:     Benoît Cousson <bcousson@...libre.com>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>, broonie@...nel.org,
        linus.walleij@...aro.org, stable@...r.kernel.org,
        linux-spi@...r.kernel.org, linux-omap@...r.kernel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        letux-kernel@...nphoenux.org, kernel@...a-handheld.com
Subject: Re: [PATCH v2] DTS: ARM: gta04: introduce legacy spi-cs-high to make
 display work again

* H. Nikolaus Schaller <hns@...delico.com> [190920 09:12]:
> commit 6953c57ab172 "gpio: of: Handle SPI chipselect legacy bindings"
> 
> did introduce logic to centrally handle the legacy spi-cs-high property
> in combination with cs-gpios. This assumes that the polarity
> of the CS has to be inverted if spi-cs-high is missing, even
> and especially if non-legacy GPIO_ACTIVE_HIGH is specified.
> 
> The DTS for the GTA04 was orginally introduced under the assumption
> that there is no need for spi-cs-high if the gpio is defined with
> proper polarity GPIO_ACTIVE_HIGH.
> 
> This was not a problem until gpiolib changed the interpretation of
> GPIO_ACTIVE_HIGH and missing spi-cs-high.
> 
> The effect is that the missing spi-cs-high is now interpreted as CS being
> low (despite GPIO_ACTIVE_HIGH) which turns off the SPI interface when the
> panel is to be programmed by the panel driver.
> 
> Therefore, we have to add the redundant and legacy spi-cs-high property
> to properly activate CS.

Thanks applying into fixes.

Tony