linux-kernel - Re: [PATCH v2 1/4] spi: dt-bindings: Introduce spi-mosi-idle-low flag

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Date:   Fri, 12 May 2023 08:54:19 +0200
From:   Börge Strümpfel <boerge.struempfel@...il.com>
To:     Mark Brown <broonie@...nel.org>
Cc:     bstruempfel@...ratronik.de, andy.shevchenko@...il.com,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Conor Dooley <conor+dt@...nel.org>,
        Shawn Guo <shawnguo@...nel.org>,
        Sascha Hauer <s.hauer@...gutronix.de>,
        Pengutronix Kernel Team <kernel@...gutronix.de>,
        Fabio Estevam <festevam@...il.com>,
        NXP Linux Team <linux-imx@....com>,
        linux-spi@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v2 1/4] spi: dt-bindings: Introduce spi-mosi-idle-low flag

Am Fr., 12. Mai 2023 um 05:30 Uhr schrieb Mark Brown <broonie@...nel.org>:
>
> On Fri, May 12, 2023 at 01:13:14AM +0200, Boerge Struempfel wrote:
> > Some spi controller switch the mosi line to high, whenever they are
> > idle. This may not be desired in all use cases. For example neopixel
> > leds can get confused and flicker due to misinterpreting the idle state.
> > Therefore, we introduce a new spi-mode bit, with which the idle behaviour
> > can be overwritten on a per device basis.
> >
> > Signed-off-by: Boerge Struempfel <bstruempfel@...ratronik.de>
> > ---
> >  .../devicetree/bindings/spi/spi-peripheral-props.yaml       | 6 ++++++
>
> If this is always required for a given device (which I'd expect to be
> the case) why configure it through DT?  I know we've got some legacy
> stuff like that but not all legacy DT choices were good and no need to
> continue the pattern.

Yes this will always be the case for specific spi-device, spi-controller
combinations. Just to make sure, that I understand your suggestion
correctly: You propose to check from the specific spi-device-driver, if
the spi-controller supports this particular mode-bit, and then set it if
it does and thereby loose the need for the DT entry completely?