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From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To: Rob Herring <robh+dt@kernel.org>
Cc: "Krzysztof Wilczyński" <kw@linux.com>,
	"Zev Weiss" <zev@bewilderbeest.net>,
	"Rafael J. Wysocki" <rafael@kernel.org>,
	"Daniel Vetter" <daniel.vetter@ffwll.ch>,
	"Jeremy Kerr" <jk@codeconstruct.com.au>,
	"Francis Laniel" <laniel_francis@privacyrequired.com>,
	"moderated list:ARM/ASPEED MACHINE SUPPORT"
	<linux-aspeed@lists.ozlabs.org>,
	"Frank Rowand" <frowand.list@gmail.com>,
	"OpenBMC Maillist" <openbmc@lists.ozlabs.org>,
	"Andy Shevchenko" <andy.shevchenko@gmail.com>,
	"Andrey Konovalov" <andreyknvl@gmail.com>,
	"Alexey Dobriyan" <adobriyan@gmail.com>,
	devicetree <devicetree@vger.kernel.org>,
	"Kees Cook" <keescook@chromium.org>,
	"Jonathan Cameron" <Jonathan.Cameron@huawei.com>,
	"Dan Williams" <dan.j.williams@intel.com>,
	"linux-arm Mailing List" <linux-arm-kernel@lists.infradead.org>,
	"Daniel Axtens" <dja@axtens.net>,
	"Andy Shevchenko" <andy@kernel.org>,
	"Andrew Jeffery" <andrew@aj.id.au>,
	"Nick Desaulniers" <ndesaulniers@google.com>,
	"Linux Kernel Mailing List" <linux-kernel@vger.kernel.org>,
	"Andrew Morton" <akpm@linux-foundation.org>,
	"Heiner Kallweit" <hkallweit1@gmail.com>
Subject: Re: [PATCH 0/9] Dynamic DT device nodes
Date: Fri, 8 Oct 2021 07:41:06 +0200	[thread overview]
Message-ID: <YV/Z8mSCxhk3rD8Z@kroah.com> (raw)
In-Reply-To: <CAL_JsqLk-CqKVgWp3=XccHrCdQgdGoezB6=HAXMDe1Q5R4-0HA@mail.gmail.com>

On Thu, Oct 07, 2021 at 03:03:43PM -0500, Rob Herring wrote:
> On Thu, Oct 7, 2021 at 10:41 AM Zev Weiss <zev@bewilderbeest.net> wrote:
> >
> > On Thu, Oct 07, 2021 at 03:31:39AM PDT, Greg Kroah-Hartman wrote:
> > >On Thu, Oct 07, 2021 at 02:05:41AM -0700, Zev Weiss wrote:
> > >> On Thu, Oct 07, 2021 at 12:04:41AM PDT, Andy Shevchenko wrote:
> > >> > On Thu, Oct 7, 2021 at 3:10 AM Zev Weiss <zev@bewilderbeest.net> wrote:
> > >> > > This patch series is in some ways kind of a v2 for the "Dynamic
> > >> > > aspeed-smc flash chips via 'reserved' DT status" series I posted
> > >> > > previously [0], but takes a fairly different approach suggested by Rob
> > >> > > Herring [1] and doesn't actually touch the aspeed-smc driver or
> > >> > > anything in the MTD subsystem, so I haven't marked it as such.
> > >> > >
> > >> > > To recap a bit of the context from that series, in OpenBMC there's a
> > >> > > need for certain devices (described by device-tree nodes) to be able
> > >> > > to be attached and detached at runtime (for example the SPI flash for
> > >> > > the host's firmware, which is shared between the BMC and the host but
> > >> > > can only be accessed by one or the other at a time).
> > >> >
> > >> > This seems quite dangerous. Why do you need that?
> > >>
> > >> Sometimes the host needs access to the flash (it's the host's firmware,
> > >> after all), sometimes the BMC needs access to it (e.g. to perform an
> > >> out-of-band update to the host's firmware).  To achieve the latter, the
> > >> flash needs to be attached to the BMC, but that requires some careful
> > >> coordination with the host to arbitrate which one actually has access to it
> > >> (that coordination is handled by userspace, which then tells the kernel
> > >> explicitly when the flash should be attached and detached).
> > >>
> > >> What seems dangerous?
> > >>
> > >> > Why can't device tree overlays be used?
> > >>
> > >> I'm hoping to stay closer to mainline.  The OpenBMC kernel has a documented
> > >> policy strongly encouraging upstream-first development:
> > >> https://github.com/openbmc/docs/blob/master/kernel-development.md
> > >>
> > >> I doubt Joel (the OpenBMC kernel maintainer) would be eager to start
> > >> carrying the DT overlay patches; I'd likewise strongly prefer to avoid
> > >> carrying them myself as additional downstream patches.  Hence the attempt at
> > >> getting a solution to the problem upstream.
> > >
> > >Then why not work to get device tree overlays to be merged properly?
> 
> TBC, it's 'just' the general purpose userspace interface to apply
> overlays that's missing.
> 
> I did suggest what's done here as overlays are kind of an overkill for
> this usecase. Much easier to write to a sysfs file than write an
> overlay, compile it with dtc, and provide it to the kernel all just to
> enable a device.
> 
> Perhaps this could also be supported in the driver model directly.
> Given the "what about ACPI question", that is probably what should be
> done unless the answer is we don't care. I think we'd just need a flag
> to create devices, but not bind automatically. Or maybe abusing
> driver_override can accomplish that.

The driver model already allows devices to be bound/unbound from
drivers, but no, it does not allow new devices to be "created" from
userspace as that is a very bus-specific thing to have happen.

If this is "just" a platform device, perhaps add that logic to the
platform bus code?

thanks,

greg k-h

  reply	other threads:[~2021-10-08  5:42 UTC|newest]

Thread overview: 33+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-10-07  0:09 Zev Weiss
2021-10-07  0:09 ` [PATCH 1/9] sysfs: add sysfs_remove_bin_file_self() function Zev Weiss
2021-10-07  5:23   ` Greg Kroah-Hartman
2021-10-07  5:58     ` Zev Weiss
2021-10-07  6:12       ` Greg Kroah-Hartman
2021-10-07  6:55         ` Zev Weiss
2021-10-07  0:09 ` [PATCH 2/9] sysfs: add growable flag to struct bin_attribute Zev Weiss
2021-10-07  0:09 ` [PATCH 3/9] lib/string: add sysfs_buf_streq() Zev Weiss
2021-10-07  0:09 ` [PATCH 4/9] of: add self parameter to __of_sysfs_remove_bin_file() Zev Weiss
2021-10-07  5:25   ` Greg Kroah-Hartman
2021-10-07  0:09 ` [PATCH 5/9] of: add self parameter to of_update_property() Zev Weiss
2021-10-07  5:26   ` Greg Kroah-Hartman
2021-10-07  0:09 ` [PATCH 6/9] of: add support for 'dynamic' DT property Zev Weiss
2021-10-08 18:51   ` Frank Rowand
2021-10-08 19:19     ` Frank Rowand
2021-10-11 13:58     ` Frank Rowand
2021-10-11 14:46       ` Frank Rowand
2021-10-11 17:35       ` Zev Weiss
2021-10-07  0:09 ` [PATCH 7/9] of: make OF_DYNAMIC selectable independently of OF_UNITTEST Zev Weiss
2021-10-08 19:01   ` Frank Rowand
2021-10-07  0:09 ` [PATCH 8/9] dt-bindings: document new 'dynamic' common property Zev Weiss
2021-10-07  5:26   ` Greg Kroah-Hartman
2021-10-07  6:03     ` Zev Weiss
2021-10-07  0:09 ` [PATCH 9/9] ARM: dts: aspeed: Add e3c246d4i BIOS flash device Zev Weiss
2021-10-07  2:46 ` [PATCH 0/9] Dynamic DT device nodes Florian Fainelli
2021-10-07  5:44   ` Zev Weiss
2021-10-07  7:04 ` Andy Shevchenko
2021-10-07  9:05   ` Zev Weiss
2021-10-07 10:31     ` Greg Kroah-Hartman
2021-10-07 15:41       ` Zev Weiss
2021-10-07 20:03         ` Rob Herring
2021-10-08  5:41           ` Greg Kroah-Hartman [this message]
2021-10-08 19:43           ` Frank Rowand

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