Re: [PATCH v1 3/3] arm64: dts: add Hi6220 mailbox node

[Mark Rutland <mark.rutland@arm.com>]

On Mon, Aug 24, 2015 at 10:18:45AM +0100, Leo Yan wrote:
> Hi Mark,
> 
> On Fri, Aug 21, 2015 at 07:40:59PM +0100, Mark Rutland wrote:
> > On Wed, Aug 19, 2015 at 10:37:35AM +0100, Leo Yan wrote:
> > > On Hi6220, below memory regions in DDR have specific purpose:
> > > 
> > >   0x05e0,0000 - 0x05ef,ffff: For MCU firmware using at runtime;
> > >   0x0740,f000 - 0x0740,ffff: For MCU firmware's section;
> > >   0x06df,f000 - 0x06df,ffff: For mailbox message data.
> > > 
> > > This patch reserves these memory regions and add device node for
> > > mailbox in dts.
> > > 
> > > Signed-off-by: Leo Yan <leo.yan@linaro.org>
> > > ---
> > >  arch/arm64/boot/dts/hisilicon/hi6220-hikey.dts | 20 +++++++++++++++++---
> > >  arch/arm64/boot/dts/hisilicon/hi6220.dtsi      |  8 ++++++++
> > >  2 files changed, 25 insertions(+), 3 deletions(-)
> > > 
> > > diff --git a/arch/arm64/boot/dts/hisilicon/hi6220-hikey.dts b/arch/arm64/boot/dts/hisilicon/hi6220-hikey.dts
> > > index e36a539..d5470d3 100644
> > > --- a/arch/arm64/boot/dts/hisilicon/hi6220-hikey.dts
> > > +++ b/arch/arm64/boot/dts/hisilicon/hi6220-hikey.dts
> > > @@ -7,9 +7,6 @@
> > >  
> > >  /dts-v1/;
> > >  
> > > -/*Reserved 1MB memory for MCU*/
> > > -/memreserve/ 0x05e00000 0x00100000;
> > > -
> > >  #include "hi6220.dtsi"
> > >  
> > >  / {
> > > @@ -28,4 +25,21 @@
> > >  		device_type = "memory";
> > >  		reg = <0x0 0x0 0x0 0x40000000>;
> > >  	};
> > > +
> > > +	reserved-memory {
> > > +		#address-cells = <2>;
> > > +		#size-cells = <2>;
> > > +		ranges;
> > > +
> > > +		mcu-buf@05e00000 {
> > > +			no-map;
> > > +			reg = <0x0 0x05e00000 0x0 0x00100000>,	/* MCU firmware buffer */
> > > +			      <0x0 0x0740f000 0x0 0x00001000>;	/* MCU firmware section */
> > > +		};
> > > +
> > > +		mbox-buf@06dff000 {
> > > +			no-map;
> > > +			reg = <0x0 0x06dff000 0x0 0x00001000>;	/* Mailbox message buf */
> > > +		};
> > > +	};
> > 
> > As far as I can see, it would be simpler to simply carve these out of the
> > memory node.
> > 
> > I don't see why you need reserved-memory here, given you're not referring to
> > these regions by phandle anyway.
> 
> - Now we have enabled EFI_STUB, so the memory node will be removed in
>   kernel:
>     efi_entry()
>       \-> allocate_new_fdt_and_exit_boot()
>             \-> update_fdt();
> 
>   Finally in kernel it cannot use memory node to carve out reseved
>   memory regions.
> 
> - On the other hand, DTS's the memory node is to "describes the
>   physical memory layout for the system"; so it's better to use it only
>   to describe the hardware info for memory. We can use reserved-memory
>   to help manage the memory regions which are reserved from software
>   perspective.

The fact that you have no-map means that the memory should not be
described to the kernel as mappable in the first place. It's wrong to
place such memory in the memory node, even if listed in reserved-memory.

If your EFI memory map describes the memory as mappable, it is wrong.

> According to upper info, we still need to use reserved-memory node to
> depict the reserved memory regions. i have no knowledge about EFI_STUB,
> so please confirm or correct as needed.

If the memory shouldn't be mapped, it should neither be in the memory
node nor EFI memory map (with attributes allowing it to be mapped) to
begin with.

As far as I can see you do not need to use reserved-memory.

Thanks,
Mark.