linux-kernel - Re: [PATCH 7/8] arm64: dts: Add Pensando Elba SoC support

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Date:   Sun, 28 Mar 2021 18:07:50 -0700
From:   Brad Larson <brad@...sando.io>
To:     Serge Semin <fancer.lancer@...il.com>
Cc:     Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Arnd Bergmann <arnd@...db.de>,
        Linus Walleij <linus.walleij@...aro.org>,
        Bartosz Golaszewski <bgolaszewski@...libre.com>,
        Mark Brown <broonie@...nel.org>,
        Adrian Hunter <adrian.hunter@...el.com>,
        Ulf Hansson <ulf.hansson@...aro.org>,
        Olof Johansson <olof@...om.net>,
        "open list:GPIO SUBSYSTEM" <linux-gpio@...r.kernel.org>,
        linux-spi <linux-spi@...r.kernel.org>,
        linux-mmc <linux-mmc@...r.kernel.org>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 7/8] arm64: dts: Add Pensando Elba SoC support

On Thu, Mar 4, 2021 at 12:03 AM Serge Semin <fancer.lancer@...il.com> wrote:
>
> On Wed, Mar 03, 2021 at 07:41:40PM -0800, Brad Larson wrote:
> > Add Pensando common and Elba SoC specific device nodes
> > and corresponding binding documentation.
>
> This also needs to be split up into sub-patches seeing these are
> unrelated changes like device bindings update, new platform DT file.

In patchset v2 this is split into sub-patches.

> What about converting this file to DT-schema and adding new HW
> bindings in there?

Converted existing file devicetree/bindings/spi/cadence-quadspi.txt to
YAML schema.

> > +&spi0 {
> > +     num-cs = <4>;
>
> > +     cs-gpios = <&spics 0 0>, <&spics 1 0>, <&porta 1 0>, <&porta 7 0>;
>
> Oh, you've got four peripheral SPI devices connected with only two native CS
> available. Hmm, then I don't really know a better way, but just to forget about
> the native DW APB CS functionality and activate the direct driving of
> all the CS-pins at the moment of the DW APB SPI controller probe
> procedure. Then indeed you'll need a custom CS function defined in the DW APB
> SPI driver to handle that.

Yes, with an Elba SoC specific gpio driver.

> So that GPIO-controller is just a single register which provides a way
> to toggle the DW APB SPI CS-mode together with their output value.
> If so and seeing there are a few more tiny spaces of config
> registers added to eMMC, PCI, etc DT node, I suppose all of them
> belong to some bigger config space of the SoC. Thus I'd suggest to at
> least implement them as part of a System Controller DT node. Then use
> that device service to switch on/off corresponding functionality.
> See [2] and the rest of added to the kernel DTS files with
> syscon-nodes for example.
>
> [2] Documentation/devicetree/bindings/mfd/syscon.yaml

To us it was more understandable to implement a standard gpio driver
for the spi chip-selects.