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

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Message-ID: <CACna6rweJuyqZ-sVe-DT7yaX4pPLXt8H++BdsZ7+EyzSzoeRoQ@mail.gmail.com>
Date:	Thu, 21 May 2015 10:25:11 +0200
From:	Rafał Miłecki <zajec5@...il.com>
To:	Brian Norris <computersforpeace@...il.com>
Cc:	Geert Uytterhoeven <geert@...ux-m68k.org>,
	"linux-mtd@...ts.infradead.org" <linux-mtd@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Stephen Warren <swarren@...dotorg.org>,
	Marek Vasut <marex@...x.de>,
	linux-spi <linux-spi@...r.kernel.org>
Subject: Re: [PATCH] Documentation: dt: mtd: replace "nor-jedec" binding with "jedec,spi-nor"

On 21 May 2015 at 10:15, Brian Norris <computersforpeace@...il.com> wrote:
> On Thu, May 21, 2015 at 10:01:05AM +0200, Rafał Miłecki wrote:
>> On 21 May 2015 at 09:25, Brian Norris <computersforpeace@...il.com> wrote:
>> > (trim CC a bit, as this is no longer a DT binding question)
>> >
>> > On Thu, May 21, 2015 at 09:12:25AM +0200, Rafał Miłecki wrote:
>> >> On 20 May 2015 at 23:35, Brian Norris <computersforpeace@...il.com> wrote:
>> >> > On Tue, May 19, 2015 at 09:27:50AM +0200, Rafał Miłecki wrote:
>> >> >> On 19 May 2015 at 03:34, Brian Norris <computersforpeace@...il.com> wrote:
>> >> >> > So how about the following patch? It seems like we'll need to be able to
>> >> >> > ignore useless 'modalias' values in cases like this:
>> >> >> >
>> >> >> >         // modalias = "shinynewdevice"
>> >> >> >         compatible = "myvendor,shinynewdevice", "jedec,spi-nor";
>> >> >> >
>> >> >> > and also if somebody leaves off the entire shinynewdevice string:
>> >> >> >
>> >> >> >         // modalias = "spi-nor"
>> >> >> >         compatible = "jedec,spi-nor";
>> >> >> >
>> >> >> > So we rework the spi-nor library to not reject "bad" names, and just
>> >> >> > fall back to autodetection, and we add the .of_match_table to properly
>> >> >> > catch all "jedec,spi-nor".
>> >> >>
>> >> >> That's nice but what about platforms using platform data instead of
>> >> >> DT? I would like to use some kind of "spi-nor" (with some prefix
>> >> >> *maybe*) for them too.
>> >> >
>> >> > For platform devices, you might as well just use the name of the driver,
>> >> > which is 'm25p80'. Isn't that how most platform devices are matched with
>> >> > drivers?
>> >>
>> >> Yes and I think it's ugly because it keeps causing the warning about
>> >> read flash model not matching specified one (m25p80).
>> >
>> > Sure, I agree.
>> >
>> >> Are you
>> >> seriously not going to allow platform stuff *clearly* request flash
>> >> model detection (JEDEC RDID OP)? Just because they don't use DT?
>> >
>> > No, this isn't about "allowing" anything. It's just that my primary
>> > concern was to get the DT binding straightened out properly. Linus'
>> > current tree now has the proper binding, but the m25p80.c code doesn't
>> > quite bind properly. It will work if "jedec,spi-nor" is the first
>> > entry in the compatible property (and so it becomes the 'modalias', but
>> > not second, third, etc. So my patch fixes that properly.
>> >
>> > Now, the secondary concern is that you want platform devices to specify
>> > something generic, and that doesn't yield a "found X, expected Y"
>> > message. I'm perfectly fine with fixing that too, if you have a patch
>> > for it. What do you propose?
>>
>> Maybe I wasn't clear enough. I was going to start using struct
>> flash_platform_data with
>> .type = "spi-nor",
>> but your proposed patch removes support for such name.
>
> Ah, OK. So that's the part I was overlooking.
>
>> While I like matching DT *clearly* against the whole "jedec,spi-nor"
>> string (really, I'm all for it), I'm confused what I should use for
>> platform stuff now. I don't have any proposal as my initial plan was
>> exactly to use this "spi-nor".
>> I guess I don't want to re-add support for "spi-nor" (as you just
>> proposed to remove it),
>
> I wasn't really trying to remove "spi-nor", that was mostly a side
> effect.

OK, I think we understand each other now :)


>> so I think I have to bounce the question: what
>> alternative do you propose?
>
> I think your comments suggest that I shouldn't be removing "spi-nor"
> from m25p_ids[] nor from this block:
>
>         if (data && data->type)
>                 flash_name = data->type;
>         else if (!strcmp(spi->modalias, "spi-nor"))
>                 flash_name = NULL; /* auto-detect */
>         else
>                 flash_name = spi->modalias;
>
> So it stays in both m25p_ids[] and .of_match_table.
>
> I suppose that can work. It then allows people to do weird stuff like:
>
>         compatible = "idontknowwhatimdoing,spi-nor";
>
> in their device tree. But other than that, there's not much downside I don't
> think.

It sounds like a reasonable solution. I guess there isn't a perfect
one. Even if we decide to go for sth like "jedec-spi-nor", there
always will be a chance of someone using
compatible = "idontknowwhatimdoing,jedec-spi-nor";
So if you rework your patch to leave "spi-nor" support in m25p_ids and
conditions block, it should be OK.

-- 
Rafał
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