Re: [Xen-devel] [PATCH v5 4/7] xen: introduce mfn_init macro

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

On Tue, 4 Dec 2018, Jan Beulich wrote:
> >>> On 03.12.18 at 22:03, <sstabellini@xxxxxxxxxx> wrote:
> > To be used in constant initializations of mfn_t variables, such as:
> > 
> > static mfn_t node = mfn_init(MM_ADDR);
> > 
> > It is necessary because static inline functions cannot be used as static
> > initializers.
> 
> We had been at this point once (quite some time ago), and got
> away without such an addition. Did you try to find that old
> discussion? Are there any new reasons to have such a construct?
> Do you need this for other than setting a value to INVALID_MFN,
> in which case INVALID_MFN_INITIALIZER ought to be suitable?
> 
> This is not to say I'm entirely opposed.
> 
> If we were to have such a construct, I wonder though whether
> mfn_init() is suitable as a name. Simply MFN() perhaps, and then
> also consistently have GFN() and DFN()?

Hi Jan,

I am happy with any name, and MFN() together with GFN() and DFN() look
like a good option.

The reason why it is needed is that without it I cannot introduce a
statically initialized array of mfn_t type like the one in the following
patch in the series:

+static const struct pm_access pm_node_access[] = {
+    /* MM_RPU grants access to all RPU Nodes.  */
+    [NODE_RPU] = { mfn_init(MM_RPU) },
+    [NODE_RPU_0] = { mfn_init(MM_RPU) },
+    [NODE_RPU_1] = { mfn_init(MM_RPU) },
+    [NODE_IPI_RPU_0] = { mfn_init(MM_RPU) },

[...]

Where MM_RPU is a mfn, and the NODE_* are IDs defined as enum:

#define MM_RPU  0xff9a0

enum pm_node_id {
        NODE_RPU = 6,
        NODE_RPU_0,
        NODE_RPU_1,

[...]


Originally I had:

  [NODE_RPU] = { MM_RPU },

but I changed the type to be mfn_t to address one of Julien's comments.
You might get a better idea of the issue if you give a look at this
branch:

http://xenbits.xenproject.org/git-http/people/sstabellini/xen-unstable.git 
zynqmp-v5

See:

xen/include/asm-arm/platforms/xilinx-zynqmp-eemi.h
xen/arch/arm/platforms/xilinx-zynqmp-eemi.c

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