linux-kernel - Re: [PATCH] Documentation: dt: mtd: replace "nor-jedec" binding with "jedec,spi-nor"

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Date:	Thu, 14 May 2015 22:26:41 +0200
From:	Geert Uytterhoeven <geert@...ux-m68k.org>
To:	Brian Norris <computersforpeace@...il.com>
Cc:	Stephen Warren <swarren@...dotorg.org>,
	Rob Herring <robh+dt@...nel.org>,
	Pawel Moll <pawel.moll@....com>,
	Mark Rutland <mark.rutland@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Kumar Gala <galak@...eaurora.org>,
	MTD Maling List <linux-mtd@...ts.infradead.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Marek Vasut <marex@...x.de>,
	Rafał Miłecki <zajec5@...il.com>
Subject: Re: [PATCH] Documentation: dt: mtd: replace "nor-jedec" binding with "jedec,spi-nor"

On Thu, May 14, 2015 at 7:46 PM, Stephen Warren <swarren@...dotorg.org> wrote:
> On 05/14/2015 11:32 AM, Brian Norris wrote:
>> In commit 8ff16cf77ce3 ("Documentation: devicetree: m25p80: add
>> "nor-jedec"
>> binding"), we added a generic "nor-jedec" binding to catch all
>> mostly-compatible SPI NOR flash which can be detected via the READ ID
>> opcode (0x9F). This was discussed and reviewed at the time, however
>> objections have come up since then as part of this discussion:
>>
>>    http://lkml.kernel.org/g/20150511224646.GJ32500@ld-irv-0074
>>
>> It seems the parties involved agree that "jedec,spi-nor" does a better
>> job of capturing the fact that this is SPI-specific, not just any NOR
>> flash.
>>
>> This binding was only merged for v4.1-rc1, so it's still OK to change
>> the naming.
>>
>> At the same time, let's move the documentation to a better name.
>>
>> Next up: prune the m25p_ids[] table to the minimal necessary listing, so
>> we can stop referring to code (drivers/mtd/devices/m25p80.c) from the
>> documentation.
>
> There's no need to change the code to update the documentation. Simply paste
> the list of valid device IDs into the documentation. The binding
> documentation needs to be completely standalone anyway. Binding
> documentation should never refer to Linux driver code as part of their
> definition.
>
> You can never remove the currently-supported device-specific IDs from the
> driver, since existing DTs need to continue working forever, even with
> future drivers/kernels.
>
> The binding document should also always include a complete list of supported
> flash devices. Standard practice is that the DT compatible property contains
> a list of compatible values, starting with the device-specific value, and
> followed by any generic values. All of those values should be standardized
> and specified in the DT documentation, even if the DT binding is written in
> such a way that a compliant driver need only actively match on the generic
> value. The device-specific values may not be used today, but are present in
> case some device-specific workaround needs to be retro-actively
> implemented/enabled, since that needs to happen for existing DTs too.

Indeed, all supported flash devices should be listed in the DT binding
documentation, so checkpatch can validate dts changes:

$ scripts/checkpatch.pl -f arch/arm/boot/dts/r8a7791-koelsch.dts

[...]

WARNING: DT compatible string "spansion,s25fl512s" appears
un-documented -- check ./Documentation/devicetree/bindings/
#493: FILE: arch/arm/boot/dts/r8a7791-koelsch.dts:493:
+ compatible = "spansion,s25fl512s", "nor-jedec";

>> I'd *really* like to get an 'ack' from a DT maintainer for this, those
>> those
>> are apparently very hard to come by. And I'd really not like to have to
>> revisit
>> this again in a few weeks. We have patches getting queued up for 4.2 that
>> are
>> using the "nor-jedec" binding, and I'd like to nip those in the bud ASAP.
>
>
> I am not a DT maintainer, but the DT documentation part of this change:
> Acked-by: Stephen Warren <swarren@...dia.com>

Likewise,
Acked-by: Geert Uytterhoeven <geert+renesas@...der.be>

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.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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