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From:   Rob Herring <robh@kernel.org>
Date:   Wed, 13 Feb 2019 14:30:44 -0600
Message-ID: <CAL_Jsq+qmBrXVLoD8FzgB589xET3isnqMsAxRiJJDvQyu+ZfiQ@mail.gmail.com>
Subject: Re: [RFC v7 2/5] dt-bindings: pstore-block: new support for blkoops
To:     liaoweixiong <liaoweixiong@allwinnertech.com>
Cc:     Kees Cook <keescook@chromium.org>,
        Anton Vorontsov <anton@enomsg.org>,
        Colin Cross <ccross@android.com>,
        Tony Luck <tony.luck@intel.com>,
        Jonathan Corbet <corbet@lwn.net>,
        Mark Rutland <mark.rutland@arm.com>,
        Mauro Carvalho Chehab <mchehab+samsung@kernel.org>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        "David S. Miller" <davem@davemloft.net>,
        Andrew Morton <akpm@linux-foundation.org>,
        Nicolas Ferre <nicolas.ferre@microchip.com>,
        Arnd Bergmann <arnd@arndb.de>,
        Linux Doc Mailing List <linux-doc@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        devicetree@vger.kernel.org
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On Wed, Feb 13, 2019 at 7:51 AM liaoweixiong
<liaoweixiong@allwinnertech.com> wrote:
>
>
> On 2019-01-31 00:07, Rob Herring wrote:> On Wed, Jan 23, 2019 at
> 08:05:13PM +0800, liaoweixiong wrote:
> >> Create DT binding document for blkoops.
> >>
> >> Signed-off-by: liaoweixiong <liaoweixiong@allwinnertech.com>
> >> ---
> >>  .../devicetree/bindings/pstore-block/blkoops.txt   | 32 ++++++++++++++++++++++
> >
> > /bindings/pstore/...
> >
> > I wouldn't call it blkoops either. I believe ramoops is called that to
> > maintain compatibility keeping the same kernel module name that
> > preceeded pstore.
> >
>
> Fixed.
>
> In addition, I don't known whether should we move
> ramreserved-memory/ooos.txt to /bindings/pstore. This is for maintainer
> to decide, and do it on other patch.
>
> >>  MAINTAINERS                                        |  1 +
> >>  2 files changed, 33 insertions(+)
> >>  create mode 100644 Documentation/devicetree/bindings/pstore-block/blkoops.txt
> >>
> >> diff --git a/Documentation/devicetree/bindings/pstore-block/blkoops.txt b/Documentation/devicetree/bindings/pstore-block/blkoops.txt
> >> new file mode 100644
> >> index 0000000..a25835b
> >> --- /dev/null
> >> +++ b/Documentation/devicetree/bindings/pstore-block/blkoops.txt
> >> @@ -0,0 +1,32 @@
> >> +Blkoops oops logger
> >> +===================
> >> +
> >> +Blkoops provides a block partition for oops, excluding panics now, so they can
> >> +be recovered after a reboot.
> >> +
> >> +Any space of block partition will be used for a circular buffer of oops records.
> >> +These records have a configurable size, with a size of 0 indicating that they
> >> +should be disabled.
> >> +
> >> +"partition-size" and at least one of "dmesg-size" or "pmsg-size" must be set
> >> +non-zero, but are otherwise optional as listed below.
> >> +
> >> +Blkoops will take value from Kconfig if device tree do not set, but settings
> >> +from module parameters can also overwrite them.
> >
> > That's all kernel details not relevant to the binidng.
> >
>
> Deleted.
>
> >> +
> >> +Required properties:
> >> +
> >> +- compatible: must be "blkoops".
> >> +
> >> +- partition-size: size in kbytes, must be a multiple of 4.
> >
> > This seems unnecessary given a partition has a known size.
> >
>
> partition-size is necessary for psotre/blk. User should tell pstore/blk
> how large space can it use.

The partition table says how big a partition is. If you only want to
use part of it, then make the partition smaller or use a file system.
This is a solved problem, so we don't need a new way in DT to handle
this.

> >> +Optional properties:
> >> +
> >> +- partition-path: strings must begin with "/dev", tell blkoops which partition
> >> +  it can used. If it is not set, blkoops will drop all data when reboot.
> >
> > No. '/dev/...' is a Linux thing and doesn't belong in DT.
> >
> > You should define a partition UUID and/or label and the kernel can find
> > the right partition to use.
> >
>
> pstore/blk do general read/write by filp_open/kernel_read/kernel_write,
> which need device path.
> In addition, i have no idea how to use UUID and/or label to do general
> read/write on kernel layer, can you give me a tip?

The kernel can mount a filesystem by label or UUID though I think
those are filesystem UUID and label, not partition UUID and label. But
certainly bootloaders find the EFI system partition by UUID.

Rob