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From:   Chuanhong Guo <gch981213@gmail.com>
Date:   Wed, 26 Feb 2020 09:31:33 +0800
Message-ID: <CAJsYDVKqcd-ytLLf5zKqs8DfjPAa5ELCX53OiPDAi-tDnLd=Eg@mail.gmail.com>
Subject: Re: [PATCH 0/2] rewrite mtk-quadspi spi-nor driver with spi-mem
To:     Rob Herring <robh@kernel.org>, Mark Brown <broonie@kernel.org>
Cc:     linux-mediatek@lists.infradead.org, linux-spi@vger.kernel.org,
        linux-mtd@lists.infradead.org,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@vger.kernel.org>,
        Miquel Raynal <miquel.raynal@bootlin.com>,
        Richard Weinberger <richard@nod.at>,
        Vignesh Raghavendra <vigneshr@ti.com>,
        Mark Rutland <mark.rutland@arm.com>,
        Matthias Brugger <matthias.bgg@gmail.com>,
        linux-arm-kernel@lists.infradead.org,
        open list <linux-kernel@vger.kernel.org>
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Hi!

On Wed, Feb 26, 2020 at 1:31 AM Rob Herring <robh@kernel.org> wrote:
>
> On Thu, Feb 20, 2020 at 07:58:06AM +0800, Chuanhong Guo wrote:
> > Hi!
> >
> > On Tue, Feb 18, 2020 at 8:55 PM Mark Brown <broonie@kernel.org> wrote:
> > > This is an ABI break so you shouldn't be doing this, if the existing
> > > binding works it should continue to work.
> >
> > The missing spi-max-frequency is the only part preventing old
> > device tree to work with this driver.
> > If the goal is to make existing dt binding work, I could patch dt using
> > of_add_property in v2. I saw similar device tree patching for legacy
> > bindings in pinctrl-single driver.

I just noticed that of_add_property isn't a exported symbol, which means that
device tree patching isn't possible unless driver is builtin.

>
> You should should really only need 'spi-max-frequency' if the max freq
> is less than the minimum of the host and device max freq.

But current spi framework forces that a "spi-max-frequency" property
is present. [0]
Should we patch spi framework then?

[0] https://elixir.bootlin.com/linux/latest/source/drivers/spi/spi.c#L1951
-- 
Regards,
Chuanhong Guo