linux-kernel - Re: [PATCH 2/2] spi: spidev: add new mediatek support

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Message-ID: <CAFGrd9pKuMsjmqg=mPsrwn=u7pCHdHEGaiW5PnwA_=TSte5sDw@mail.gmail.com>
Date:   Mon, 23 Jan 2023 15:57:59 +0100
From:   Alexandre Mergnat <amergnat@...libre.com>
To:     Michael Walle <michael@...le.cc>
Cc:     broonie@...nel.org, devicetree@...r.kernel.org,
        krzysztof.kozlowski+dt@...aro.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-mediatek@...ts.infradead.org, linux-spi@...r.kernel.org,
        matthias.bgg@...il.com, robh+dt@...nel.org
Subject: Re: [PATCH 2/2] spi: spidev: add new mediatek support

Le lun. 23 janv. 2023 à 11:44, Michael Walle <michael@...le.cc> a écrit :
>
> Hi,
>
> Am 2023-01-23 10:37, schrieb Alexandre Mergnat:
> > Le ven. 20 janv. 2023 à 09:20, Michael Walle <michael@...le.cc> a écrit
> > :
> >>
> >> From: Alexandre Mergnat <amergnat@...libre.com>
> >>
> >> > Add the "mediatek,genio" compatible string to support Mediatek
> >> > SPI controller on the genio boards.
> >>
> >> What is the use case of having the spidev? What if I want to
> >> connect a device with a linux driver to it? It seems like you
> >> just want to expose the SPI bus on the pin header. There was a
> >> similar discussion for a mikrobus connector [1].
> >>
> > Yes I want to expose the SPI on the pin header for two reasons:
>
> Then "mediatek,genio" doesn't really describe the hardware, does it?
> If you read that linked thread, NXP was also trying exposing the SPI
> bus on a pin header. IMHO this is just misusing the userspace spi-dev.
>
> That being said, exposing something on a pinheader (or on a standardized
> connector) seems like a common thing and we should be working towards
> a good solution. I still think Robs proposal for the mikrobus connector
> makes also sense for your case.
>

I don't think this is the same case. For the mikrobus case, it's
consistent to have a connector because it fit with other "add-on"
board which can be plug on the "mother board".
Here I've just a simple debug pin header. I've taken a look at
raspberry pi and Beaglebone black DTS, they don't use connector, but
DTS overlay to enable SPI. I think you're right when you say that I'm
misusing the userspace spi-dev.