From: Ezequiel Garcia <ezequiel.garcia@free-electrons.com>
To: Brian Norris <computersforpeace@gmail.com>
Cc: Mark Rutland <mark.rutland@arm.com>,
devicetree@vger.kernel.org, Russell King <linux@arm.linux.org.uk>,
Pawel Moll <pawel.moll@arm.com>,
Alexander Shiyan <shc_work@mail.ru>,
Ian Campbell <ijc+devicetree@hellion.org.uk>,
Artem Bityutskiy <dedekind1@gmail.com>,
Rob Herring <rob.herring@calxeda.com>,
linux-mtd@lists.infradead.org,
Haojian Zhuang <haojian.zhuang@gmail.com>,
Stephen Warren <swarren@wwwdotorg.org>,
Eric Miao <eric.y.miao@gmail.com>,
David Woodhouse <dwmw2@infradead.org>, Pekon Gupta <pekon@ti.com>
Subject: Re: [PATCH v5 1/3] mtd: nand: gpio: Add DT property to automatically determine bus width
Date: Sat, 30 Nov 2013 08:17:22 -0300 [thread overview]
Message-ID: <20131130111721.GA2330@localhost> (raw)
In-Reply-To: <20131130091556.GD29397@norris.computersforpeace.net>
Brian,
On Sat, Nov 30, 2013 at 01:15:56AM -0800, Brian Norris wrote:
>
> > Can anyone help me understand if there's *any* valid use case where we
> > want to specify a-priori the bus width, considering it's completely
> > discoverable at run-time?
>
> I think the primary use case should be to reflect a limitation in the
> hardware (besides just the flash chip). It can mean that the controller
> itself only supports one bus width, or that the board is only wired up
> for x8, for instance.
>
What do you mean by "reflect a limitation" of the hardware?
Maybe I'm not really following you, but it sounds as you're mixing up
the NAND device buswidth and the memory controller buswidth. At least
I consider them as two different parameters for two different pieces
of hardware.
Consider OMAP, just as an example. We currently have two DT properties:
1. nand-bus-width: not related to OMAP but kernel wide. It's supposed
to specify the devices buswidth.
2. gpmc,device-width: It specifies how the controller should be
configured (it doesn't really specify hardware, but configuration,
sadly).
I now realise maybe this piece of DT binding is not a good example of DT.
Anyway, once again: Why would we need to set "nand-bus-width" to specify
the flash device width given we can discover that as soon as the NAND
is detected?
Notice, that this discussion is independent of the discussion about removing
the NAND_BUSWIDTH_AUTO. It's just about removing a DT property for a
parameter that's runtime configurable.
--
Ezequiel García, Free Electrons
Embedded Linux, Kernel and Android Engineering
http://free-electrons.com
WARNING: multiple messages have this Message-ID (diff)
From: Ezequiel Garcia <ezequiel.garcia-wi1+55ScJUtKEb57/3fJTNBPR1lH4CV8@public.gmane.org>
To: Brian Norris <computersforpeace-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
Cc: Alexander Shiyan <shc_work-JGs/UdohzUI@public.gmane.org>,
linux-mtd-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org,
Mark Rutland <mark.rutland-5wv7dgnIgG8@public.gmane.org>,
devicetree-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
Ian Campbell
<ijc+devicetree-KcIKpvwj1kUDXYZnReoRVg@public.gmane.org>,
Russell King <linux-lFZ/pmaqli7XmaaqVzeoHQ@public.gmane.org>,
Pawel Moll <pawel.moll-5wv7dgnIgG8@public.gmane.org>,
Artem Bityutskiy
<dedekind1-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>,
Stephen Warren <swarren-3lzwWm7+Weoh9ZMKESR00Q@public.gmane.org>,
Rob Herring <rob.herring-bsGFqQB8/DxBDgjK7y7TUQ@public.gmane.org>,
Haojian Zhuang
<haojian.zhuang-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>,
Eric Miao <eric.y.miao-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>,
David Woodhouse <dwmw2-wEGCiKHe2LqWVfeAwA7xHQ@public.gmane.org>,
Pekon Gupta <pekon-l0cyMroinI0@public.gmane.org>
Subject: Re: [PATCH v5 1/3] mtd: nand: gpio: Add DT property to automatically determine bus width
Date: Sat, 30 Nov 2013 08:17:22 -0300 [thread overview]
Message-ID: <20131130111721.GA2330@localhost> (raw)
In-Reply-To: <20131130091556.GD29397-7ciq9WCbhwJWVhifINYOO1poFGfAdsVx5NbjCUgZEJk@public.gmane.org>
Brian,
On Sat, Nov 30, 2013 at 01:15:56AM -0800, Brian Norris wrote:
>
> > Can anyone help me understand if there's *any* valid use case where we
> > want to specify a-priori the bus width, considering it's completely
> > discoverable at run-time?
>
> I think the primary use case should be to reflect a limitation in the
> hardware (besides just the flash chip). It can mean that the controller
> itself only supports one bus width, or that the board is only wired up
> for x8, for instance.
>
What do you mean by "reflect a limitation" of the hardware?
Maybe I'm not really following you, but it sounds as you're mixing up
the NAND device buswidth and the memory controller buswidth. At least
I consider them as two different parameters for two different pieces
of hardware.
Consider OMAP, just as an example. We currently have two DT properties:
1. nand-bus-width: not related to OMAP but kernel wide. It's supposed
to specify the devices buswidth.
2. gpmc,device-width: It specifies how the controller should be
configured (it doesn't really specify hardware, but configuration,
sadly).
I now realise maybe this piece of DT binding is not a good example of DT.
Anyway, once again: Why would we need to set "nand-bus-width" to specify
the flash device width given we can discover that as soon as the NAND
is detected?
Notice, that this discussion is independent of the discussion about removing
the NAND_BUSWIDTH_AUTO. It's just about removing a DT property for a
parameter that's runtime configurable.
--
Ezequiel García, Free Electrons
Embedded Linux, Kernel and Android Engineering
http://free-electrons.com
--
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next prev parent reply other threads:[~2013-11-30 11:26 UTC|newest]
Thread overview: 34+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-11-13 11:58 [PATCH v5 1/3] mtd: nand: gpio: Add DT property to automatically determine bus width Alexander Shiyan
2013-11-13 11:58 ` Alexander Shiyan
2013-11-13 11:58 ` [PATCH v5 2/3] mtd: nand: gpio: Use devm_gpio_request_one() where possible Alexander Shiyan
2013-11-13 11:58 ` Alexander Shiyan
2013-11-13 11:58 ` [PATCH v5 3/3] mtd: nand: gpio: Add support for multichip devices Alexander Shiyan
2013-11-13 11:58 ` Alexander Shiyan
2013-11-27 1:21 ` [PATCH v5 1/3] mtd: nand: gpio: Add DT property to automatically determine bus width Brian Norris
2013-11-27 1:21 ` Brian Norris
2013-11-27 1:23 ` Brian Norris
2013-11-27 1:23 ` Brian Norris
2013-11-29 12:25 ` Ezequiel Garcia
2013-11-29 12:25 ` Ezequiel Garcia
2013-11-29 12:35 ` Alexander Shiyan
2013-11-29 12:44 ` Ezequiel Garcia
2013-11-30 9:15 ` Brian Norris
2013-11-30 9:15 ` Brian Norris
2013-11-30 11:17 ` Ezequiel Garcia [this message]
2013-11-30 11:17 ` Ezequiel Garcia
2013-11-30 18:35 ` Brian Norris
2013-11-30 18:35 ` Brian Norris
2013-11-27 4:21 ` Alexander Shiyan
2013-11-27 4:21 ` Alexander Shiyan
2013-11-27 4:34 ` Brian Norris
2013-11-27 4:34 ` Brian Norris
2013-11-29 8:56 ` Alexander Shiyan
2013-11-29 8:56 ` Alexander Shiyan
2013-11-30 9:17 ` Brian Norris
2013-11-30 9:17 ` Brian Norris
2013-12-05 2:18 ` Brian Norris
2013-12-05 2:18 ` Brian Norris
2013-12-05 7:45 ` Alexander Shiyan
2013-12-05 7:45 ` Alexander Shiyan
2013-11-27 20:16 ` Gupta, Pekon
2013-11-27 20:16 ` Gupta, Pekon
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