Re: [linux-sunxi] Re: [PATCH 1/4] brcmfmac: Add brcm, nvram_file_name dt property

From: Arnd Bergmann <arnd@arndb.de>
To: Arend Van Spriel <arend.vanspriel@broadcom.com>
Cc: devicetree <devicetree@vger.kernel.org>,
	Priit Laes <plaes@plaes.org>,
	linux-sunxi@googlegroups.com,
	"linux-wireless@vger.kernel.org" <linux-wireless@vger.kernel.org>,
	"John W . Linville" <linville@tuxdriver.com>,
	Hans de Goede <hdegoede@redhat.com>, Chen-Yu Tsai <wens@csie.org>,
	"linux-arm-kernel@lists.infradead.org"
	<linux-arm-kernel@lists.infradead.org>,
	Jonas Gorski <jonas.gorski@gmail.com>,
	Arend van Spriel <arend@broadcom.com>,
	Maxime Ripard <maxime.ripard@free-electrons.com>,
	Kalle Valo <kvalo@codeaurora.org>
Subject: Re: [linux-sunxi] Re: [PATCH 1/4] brcmfmac: Add brcm, nvram_file_name dt property
Date: Mon, 04 Jul 2016 10:55:19 +0200	[thread overview]
Message-ID: <5756670.9hMGo8oEyl@wuerfel> (raw)
In-Reply-To: <ac480a61-5bfd-5d0c-26fe-b85220ee5076@broadcom.com>

On Monday, July 4, 2016 10:41:20 AM CEST Arend Van Spriel wrote:
> On 2-7-2016 23:30, Arnd Bergmann wrote:
> > On Saturday, July 2, 2016 8:20:35 PM CEST Arend Van Spriel wrote:
> >>> If you want a separate property, then I repeat my very first
> >>> suggestion, the well defined model property.
> >>> e.g.
> >>>
> >>> brcmf@0 {
> >>>         model = "ampak,ap6210";
> >>>         compatible = "brcm,bcm4329-fmac";
> >>>         ...
> >>> };
> >>>
> >>> All device nodes may have a model property, not just the top "machine" one.
> >>
> >> I heard you the first time  I just was not sure what the implications
> >> would be to use it. Hence I suggested a vendor specific property.
> >> However, looking up and reading the definition in ePAPRv1.1 I suppose it
> >> is fine to use the model property:
> >>
> >> Property: model
> >> Value type: <string>
> >> Description:
> >> The model property value is a <string> that specifies the manufacturer’s
> >> model number of the device.
> >>
> >> The recommended format is: “manufacturer,model”, where manufacturer is a
> >> string describing the name of the manufacturer (such as a stock ticker
> >> symbol), and model specifies the model number.
> > 
> > The model property is very similar to compatible, except that there is
> > only one entry rather than a list of entries from most specific to
> > most generic.
> 
> They seem very similar, but I think there is a conceptual difference.
> The compatible property is mainly used to select the appropriate driver
> and as such the property is typically ignored by device drivers.
> Probably there are exceptions to be found.
> 
> > I think by writing the above example as
> > 
> >       compatible = "ampak,ap6210", "brcm,bcm4329-fmac";
> > 
> > we can provide the same functionality in a slightly simpler way, the driver
> > then just goes on to look for the nvram file for each entry in sequence until
> > it finds one.
> 
> Not sure why this would be simpler. Why would traversing the compatible
> string be simpler than handling the model property if present and
> otherwise fallback to the default nvram naming.

Because you have to walk the list anyway to find the other firmware files:
when you have a specialization of a device that requires listing both values
as compatible, the driver has no idea which of the entries to use, unless
you add a lookup table that adds more complexity.

	Arnd

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