LKML Archive on lore.kernel.org
 help / Atom feed
From: Andrew Jeffery <andrew@aj.id.au>
To: Rob Herring <robh@kernel.org>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>,
	Mark Rutland <mark.rutland@arm.com>,
	devicetree@vger.kernel.org,
	"Greg Kroah-Hartman" <gregkh@linuxfoundation.org>,
	Eugene.Cho@dell.com, a.amelkin@yadro.com,
	linux-kernel@vger.kernel.org, Joel Stanley <joel@jms.id.au>,
	stewart@linux.ibm.com,
	OpenBMC Maillist <openbmc@lists.ozlabs.org>,
	"moderated list:ARM/FREESCALE IMX / MXC ARM ARCHITECTURE" 
	<linux-arm-kernel@lists.infradead.org>
Subject: Re: [RFC PATCH v2 1/4] dt-bindings: misc: Add bindings for misc. BMC control fields
Date: Thu, 19 Jul 2018 11:27:13 +0930
Message-ID: <1531965433.2133841.1445577960.5C709A63@webmail.messagingengine.com> (raw)
In-Reply-To: <CAL_Jsq+YdcBe+VYBAZPvK-X9gwJyhzP4m6hAx59+2Nz0JzsKug@mail.gmail.com>

On Thu, 19 Jul 2018, at 04:37, Rob Herring wrote:
> On Tue, Jul 17, 2018 at 5:28 PM Andrew Jeffery <andrew@aj.id.au> wrote:
> >
> > On Tue, 17 Jul 2018, at 14:26, Benjamin Herrenschmidt wrote:
> > > On Mon, 2018-07-16 at 07:55 -0600, Rob Herring wrote:
> > > > If that data is one set per SoC, then i'm not that concerned having
> > > > platform-specific data in the driver. That doesn't mean the driver is
> > > > not "generic". It's still not clear to me in this thread, how much of
> > > > this is board specific, but given that you've placed all the data in
> > > > an SoC dtsi file it seems to be all per SoC.
> > >
> > > So Rob, I think that's precisely where the disconnect is.
> > >
> > > I think we all (well hopefully) agree that those few tunables don't fit
> > > in any existing subystem and aren't likely to ever do (famous last
> > > words...).
> > >
> > > Where we disagree is we want to make this parametrized via the DT, and
> > > you want us to hard wire the list in some kind of SoC driver for a
> > > given SoC family/version.
> > >
> > > The reason I think hard wiring the list in the driver is not a great
> > > solution is that that list in itself is prone to variations, possibly
> > > fairly often, between boards, vendors, versions of boards, etc...
> > >
> > > We can't know for sure every SoC tunable (out of the gazillions in
> > > those chips) are going to be needed for a given system. We know which
> > > ones we do use for ours, and that's a couple of handfuls, but it could
> > > be that Dell need a slightly different set, and so might Yadro, or so
> > > might our next board revision for that matter.
> > >
> > > Now, updating the device-tree in the board flash with whatever vendor
> > > specific information is needed is a LOT easier than getting the kernel
> > > driver constantly updated. The device-tree after all is there to
> > > reflect among other things system specific ways in which the SoC is
> > > wired and configured. This is rather close...
> >
> > Not sure this helps, but I feel that the proposal pretty closely matches what's described in Documentation/devicetree/bindings/mfd/mfd.txt. It's intended that nodes using the bindings I'm proposing are children of a 'compatible = "syscon", "simple-mfd"' node (this is the case with the features we're hoping to describe for our SoC). I should explicitly call that out.
> 
> IMO, any binding that has only those compatibles is not correct and a
> specific compatible is needed. We should be able identify a specific
> h/w block.

I didn't intend for that to get interpreted quite as literally, so apologies for that. We do have h/w-block-specific compatibles in there too. The point was to demonstrate that we're dealing (at this point, only) with mfds/syscons.

> 
> > But to go on, "simple-mfd" is effectively an alias of "simple-bus", which means its intended to match child node compatibles to drivers provided by the kernel. If we shouldn't be describing minor features of a SoC in the devicetree, doesn't this invalidate the case for simple-mfd? What is the *correct* use of simple-mfd? When is it not used to expose minor features in set of "miscellaneous system registers"? Why doesn't this proposed case fit?
> 
> I'm no fan of simple-mfd either. I think it is abused and often a sign
> of bad binding design.

Ah, yes, this is a familiar feeling when reflecting on things I've done in the past. Hence trying to understand how to use it right.

> The general problem with MFD bindings is people
> define child nodes based on what drivers they happen to have for some
> OS. DT is not the only way to instantiate drivers. Child nodes are
> really only needed when you have resources per child that need to be
> defined. For example, if the MFD has an interrupt controller and
> interrupts to sub-blocks or sub-blocks have their own clocks.
> "simple-mfd" was for when the parent node has no driver or the child
> nodes have no dependency on the parent.

Thanks for the clarification, I'll keep that in mind going forward.

Andrew

  reply index

Thread overview: 31+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-07-11  5:31 [RFC PATCH v2 0/4] sysfs interface to miscellaneous BMC controls and fields Andrew Jeffery
2018-07-11  5:31 ` [RFC PATCH v2 1/4] dt-bindings: misc: Add bindings for misc. BMC control fields Andrew Jeffery
2018-07-11 20:04   ` Rob Herring
2018-07-12  0:14     ` Benjamin Herrenschmidt
2018-07-12  0:53     ` Andrew Jeffery
2018-07-12 15:11       ` Rob Herring
2018-07-13  0:55         ` Benjamin Herrenschmidt
2018-07-13  6:31           ` Andrew Jeffery
2018-07-13 15:14             ` Alexander Amelkin
2018-07-13 18:49               ` Eugene.Cho
2018-07-13 19:03                 ` Greg KH
2018-07-13 19:06                   ` Eugene.Cho
2018-07-15 14:21                     ` Avi Fishman
2018-07-16  0:57               ` Andrew Jeffery
2018-07-16 13:55             ` Rob Herring
2018-07-17  1:04               ` Andrew Jeffery
2018-07-17  4:56               ` Benjamin Herrenschmidt
2018-07-17 23:28                 ` Andrew Jeffery
2018-07-18 19:07                   ` Rob Herring
2018-07-19  1:57                     ` Andrew Jeffery [this message]
2018-07-18 19:50                 ` Rob Herring
2018-07-18 23:58                   ` Benjamin Herrenschmidt
2018-07-19  2:28                     ` Andrew Jeffery
2018-07-19  4:35                       ` Benjamin Herrenschmidt
2018-07-20  0:07                         ` Andrew Jeffery
2018-07-20  4:56                           ` Benjamin Herrenschmidt
2018-08-10  0:22                             ` Kun Yi
2018-08-23 15:32                           ` Alexander Amelkin
2018-07-11  5:31 ` [RFC PATCH v2 2/4] Documentation: ABI: Add sysfs-devices-platform-field to testing Andrew Jeffery
2018-07-11  5:31 ` [RFC PATCH v2 3/4] misc: Add bmc-misc-ctrl Andrew Jeffery
2018-07-11  5:31 ` [RFC PATCH v2 4/4] dts: aspeed-g5: Describe VGA, SIO scratch and DAC mux fields Andrew Jeffery

Reply instructions:

You may reply publically to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=1531965433.2133841.1445577960.5C709A63@webmail.messagingengine.com \
    --to=andrew@aj.id.au \
    --cc=Eugene.Cho@dell.com \
    --cc=a.amelkin@yadro.com \
    --cc=benh@kernel.crashing.org \
    --cc=devicetree@vger.kernel.org \
    --cc=gregkh@linuxfoundation.org \
    --cc=joel@jms.id.au \
    --cc=linux-arm-kernel@lists.infradead.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=mark.rutland@arm.com \
    --cc=openbmc@lists.ozlabs.org \
    --cc=robh@kernel.org \
    --cc=stewart@linux.ibm.com \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

LKML Archive on lore.kernel.org

Archives are clonable:
	git clone --mirror https://lore.kernel.org/lkml/0 lkml/git/0.git
	git clone --mirror https://lore.kernel.org/lkml/1 lkml/git/1.git
	git clone --mirror https://lore.kernel.org/lkml/2 lkml/git/2.git
	git clone --mirror https://lore.kernel.org/lkml/3 lkml/git/3.git
	git clone --mirror https://lore.kernel.org/lkml/4 lkml/git/4.git
	git clone --mirror https://lore.kernel.org/lkml/5 lkml/git/5.git
	git clone --mirror https://lore.kernel.org/lkml/6 lkml/git/6.git
	git clone --mirror https://lore.kernel.org/lkml/7 lkml/git/7.git

	# If you have public-inbox 1.1+ installed, you may
	# initialize and index your mirror using the following commands:
	public-inbox-init -V2 lkml lkml/ https://lore.kernel.org/lkml \
		linux-kernel@vger.kernel.org linux-kernel@archiver.kernel.org
	public-inbox-index lkml


Newsgroup available over NNTP:
	nntp://nntp.lore.kernel.org/org.kernel.vger.linux-kernel


AGPL code for this site: git clone https://public-inbox.org/ public-inbox