Re: [PATCH v5 01/11] of: document bindings for reserved-memory nodes

[Tomasz Figa]

On 28.02.2014 10:54, Marek Szyprowski wrote:
> Hello,
>
> On 2014-02-26 12:51, Grant Likely wrote:
> > On Fri, 21 Feb 2014 13:25:17 +0100, Marek Szyprowski
> > <m.szyprowski@xxxxxxxxxxx> wrote:
> > > From: Grant Likely <grant.likely@xxxxxxxxxx>
> > >
> > > Reserved memory nodes allow for the reservation of static (fixed
> > > address) regions, or dynamically allocated regions for a specific
> > > purpose.
> > >
> > > Signed-off-by: Grant Likely <grant.likely@xxxxxxxxxx>
> > > [joshc: Based on binding document proposed (in non-patch form) here:
> > >
> > http://lkml.kernel.org/g/20131030134702.19B57C402A0@xxxxxxxxxxxxxxxxxxx
> > >  adapted to support #memory-region-cells]
> > > Signed-off-by: Josh Cartwright <joshc@xxxxxxxxxxxxxx>
> > > Signed-off-by: Marek Szyprowski <m.szyprowski@xxxxxxxxxxx>
> > > ---
> > >  .../bindings/reserved-memory/reserved-memory.txt   |  138
> > ++++++++++++++++++++
> > >  1 file changed, 138 insertions(+)
> > >  create mode 100644
> > Documentation/devicetree/bindings/reserved-memory/reserved-memory.txt
> > >
> > > diff --git
> > a/Documentation/devicetree/bindings/reserved-memory/reserved-memory.txt b/Documentation/devicetree/bindings/reserved-memory/reserved-memory.txt
> >
> > > new file mode 100644
> > > index 000000000000..a606ce90c9c4
> > > --- /dev/null
> > > +++
> > b/Documentation/devicetree/bindings/reserved-memory/reserved-memory.txt
> > > @@ -0,0 +1,138 @@
> > > +*** Reserved memory regions ***
> > > +
> > > +Reserved memory is specified as a node under the /reserved-memory
> > node.
> > > +The operating system shall exclude reserved memory from normal usage
> > > +one can create child nodes describing particular reserved (excluded
> > from
> > > +normal use) memory regions. Such memory regions are usually
> > designed for
> > > +the special usage by various device drivers.
> > > +
> > > +Parameters for each memory region can be encoded into the device tree
> > > +with the following nodes:
> > > +
> > > +/reserved-memory node
> > > +---------------------
> > > +#address-cells, #size-cells (required) - standard definition
> > > +    - Should use the same values as the root node
> > > +#memory-region-cells (required) - dictates number of cells used in
> > the child
> > > +                                  nodes memory-region specifier
> >
> > I still don't like this portion of the binding. I'm not convinced that
> > it is necessary in the majority of cases and it is going to be very
> > driver specific. I would rather drop it entirely from the common
> > binding. If a specific driver needs to do something like the above then
> > it can have a driver specific binding. Otherwise I think the default
> > should be a simple phandle with no arguments to a single reserved memory
> > node.
> >
> > Ben, can you weigh in on the current state of this document. I'm mostly
> > happy with it aside from my comment above. Do you think this is ready to
> > be merged?
> >
> > > +ranges (required) - standard definition
> > > +    - Should be empty
> > > +
> > > +/reserved-memory/ child nodes
> > > +-----------------------------
> > > +Each child of the reserved-memory node specifies one or more
> > regions of
> > > +reserved memory. Each child node may either use a 'reg' property to
> > > +specify a specific range of reserved memory, or a 'size' property with
> > > +optional constraints to request a dynamically allocated block of
> > memory.
> > > +
> > > +Following the generic-names recommended practice, node names should
> > > +reflect the purpose of the node (ie. "framebuffer" or "dma-pool").
> > Unit
> > > +address (@<address>) should be appended to the name if the node is a
> > > +static allocation.
> > > +
> > > +Properties:
> > > +Requires either a) or b) below.
> > > +a) static allocation
> > > +   reg (required) - standard definition
> > > +b) dynamic allocation
> > > +   size (required) - length based on parent's #size-cells
> > > +                   - Size in bytes of memory to reserve.
> > > +   alignment (optional) - length based on parent's #size-cells
> > > +                        - Address boundary for alignment of
> > allocation.
> > > +   alloc-ranges (optional) - prop-encoded-array (address, length
> > pairs).
> > > +                           - Specifies regions of memory that are
> > > +                             acceptable to allocate from.
> > > +
> > > +If both reg and size are present, then the reg property takes
> > precedence
> > > +and size is ignored.
> > > +
> > > +Additional properties:
> > > +compatible (optional) - standard definition
> > > +    - may contain the following strings:
> > > +        - shared-dma-pool: This indicates a region of memory meant
> > to be
> > > +          used as a shared pool of DMA buffers for a set of
> > devices. It can
> > > +          be used by an operating system to instanciate the
> > necessary pool
> > > +          management subsystem if necessary.
> > > +        - vendor specific string in the form
> > <vendor>,[<device>-]<usage>
> >
> > Add "Use vendor strings to identify regions dedicates for a specific
> > vendor device. For example: 'acme,framebuffer'. Platform code can use
> > vendor
> > strings to identify device specific regions"
>
> So do you want to completely drop phandle based links between device
> nodes and
> memory regions?

Huh? How this would work with regions that have to be used for multiple 
(but not all - not a default region) devices?

Best regards,
Tomasz
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