Re: [PATCH] arm64/fixmap: make notes of fixed_addresses more precisely

[Pingfan Liu <kernelfans@gmail.com>]

On Fri, Jul 31, 2020 at 8:13 PM Catalin Marinas <catalin.marinas@arm.com> wrote:
>
> On Fri, Jul 31, 2020 at 10:47:13AM +0800, Pingfan Liu wrote:
> > On Thu, Jul 30, 2020 at 7:09 PM Catalin Marinas <catalin.marinas@arm.com> wrote:
> > > On Fri, Jul 10, 2020 at 09:43:22PM +0800, Pingfan Liu wrote:
> > > > These 'compile-time allocated' memory buffers can occupy more than one
> > > > page. So improve the note about it.
> > > >
> > > > Signed-off-by: Pingfan Liu <kernelfans@gmail.com>
> > > > Cc: Catalin Marinas <catalin.marinas@arm.com>
> > > > Cc: Will Deacon <will@kernel.org>
> > > > To: linux-arm-kernel@lists.infradead.org
> > > > ---
> > > >  arch/arm64/include/asm/fixmap.h | 3 ++-
> > > >  1 file changed, 2 insertions(+), 1 deletion(-)
> > > >
> > > > diff --git a/arch/arm64/include/asm/fixmap.h b/arch/arm64/include/asm/fixmap.h
> > > > index f987b8a..318aee1 100644
> > > > --- a/arch/arm64/include/asm/fixmap.h
> > > > +++ b/arch/arm64/include/asm/fixmap.h
> > > > @@ -29,7 +29,8 @@
> > > >   * in the boot process.
> > > >   *
> > > >   * These 'compile-time allocated' memory buffers are
> > > > - * page-sized. Use set_fixmap(idx,phys) to associate
> > > > + * page-sized (or larger if used with an increment
> > > > + * higher than 1). Use set_fixmap(idx,phys) to associate
> > > >   * physical memory with fixmap indices.
> > >
> > > I don't get this. set_fixmap() only maps a page. Also, what's
> > > "increment" in this context?
> >
> > I refer to the notes in the counterpart in x86. And for the time
> > being, it is the case for the ranges (FIX_FDT, FIX_FDT_END), which may
> > cost more than one page size.
>
> OK, so increment refers to the enum increment. But if we update this, we
> also need to state that set_fixmap() only maps page-size buffers,
> otherwise one may think that set_fixmap(FIX_FDT, phys) maps the whole
> FDT. We could say that each enum increment represents a page-sized
> buffer.
What about description like:
diff --git a/arch/arm64/include/asm/fixmap.h b/arch/arm64/include/asm/fixmap.h
index f987b8a..4335800 100644
--- a/arch/arm64/include/asm/fixmap.h
+++ b/arch/arm64/include/asm/fixmap.h
@@ -28,10 +28,9 @@
  * compile time, but to set the physical address only
  * in the boot process.
  *
- * These 'compile-time allocated' memory buffers are
- * page-sized. Use set_fixmap(idx,phys) to associate
- * physical memory with fixmap indices.
- *
+ * Each enum increment in these 'compile-time allocated'
+ * memory buffers is page-sized. Use set_fixmap(idx,phys)
+ * to associate physical memory with a fixmap index.
  */

Thanks,
Pingfan

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