Re: [PATCH v2] spi: orion: support armada extended baud rates

From: Geert Uytterhoeven <geert-Td1EMuHUCqxL1ZNQvxDV9g@public.gmane.org>
To: Greg Ungerer <gerg-JBU5SbJe1FlAfugRpC6u6w@public.gmane.org>
Cc: linux-spi <linux-spi-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>,
	"devicetree-u79uwXL29TY76Z2rM5mHXA@public.gmane.org"
	<devicetree-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>
Subject: Re: [PATCH v2] spi: orion: support armada extended baud rates
Date: Fri, 5 Sep 2014 09:36:22 +0200	[thread overview]
Message-ID: <CAMuHMdWf6_yBhpNgK=wJcQqzLNJvTnC95SrqrcZyRH+jGL93vA@mail.gmail.com> (raw)
In-Reply-To: <5409057A.6090900-JBU5SbJe1FlAfugRpC6u6w@public.gmane.org>

Hi Greg,

On Fri, Sep 5, 2014 at 2:36 AM, Greg Ungerer <gerg-JBU5SbJe1FlAfugRpC6u6w@public.gmane.org> wrote:
>> Are the Orion rates and register bits a subset of the Armada ones?
>> I.e. does the Armada work with the Orion setup?
>
> The bits used by the orion are a subset (bits 0-4 of the SPI
> configuration register) of those used by the armada (bits 0-4 and
> 6-7).
>
> In practice the defined prescalar values for the orion do give
> the same divisor for the same bits set on armada. The extra bits
> on the armada let you get to lower SPI baudrates (which is more of
> a problem on the armada with its higher core clocks).

OK, so the answer is yes.

>>> This change introduces a new device tree compatible device name
>>> "armada-spi". This is used in place of "orion-spi" on the Armada SoC
>>> parts.
>>
>>> -                               compatible = "marvell,orion-spi";
>>> +                               compatible = "marvell,armada-spi";
>>
>> If the answer to my above question is yes, you want to keep
>> "marvell,orion-spi" as a fallback.
>
> Do you mean like this?
>
>   compatible = "marvell,orion-spi", "marvell,armada-spi";

No, the other way around (from most-specific to least-specific):

    compatible = "marvell,armada-spi", "marvell,orion-spi"

So the Armada version is used if available, and the Orion version
is used as a fallback.

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert-Td1EMuHUCqxL1ZNQvxDV9g@public.gmane.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds
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