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

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Date:	Wed, 26 Aug 2015 00:00:30 +0800
From:	Leo Yan <leo.yan@...aro.org>
To:	Haojian Zhuang <haojian.zhuang@...aro.org>
Cc:	Mark Rutland <mark.rutland@....com>,
	Leif Lindholm <leif.lindholm@...aro.org>,
	Rob Herring <robh+dt@...nel.org>,
	Pawel Moll <Pawel.Moll@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Kumar Gala <galak@...eaurora.org>,
	Catalin Marinas <Catalin.Marinas@....com>,
	Will Deacon <Will.Deacon@....com>,
	Jassi Brar <jassisinghbrar@...il.com>,
	Bintian Wang <bintian.wang@...wei.com>,
	Yiping Xu <xuyiping@...ilicon.com>,
	Wei Xu <xuwei5@...ilicon.com>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"guodong.xu@...aro.org" <guodong.xu@...aro.org>,
	Jian Zhang <zhangjian001@...ilicon.com>,
	Zhenwei Wang <Zhenwei.wang@...ilicon.com>,
	Haoju Mo <mohaoju@...ilicon.com>,
	Dan Zhao <dan.zhao@...ilicon.com>,
	"kongfei@...ilicon.com" <kongfei@...ilicon.com>,
	Guangyue Zeng <zengguangyue@...ilicon.com>
Subject: Re: [PATCH v1 3/3] arm64: dts: add Hi6220 mailbox node

On Tue, Aug 25, 2015 at 09:43:14PM +0800, Haojian Zhuang wrote:
> On Tue, 2015-08-25 at 11:42 +0100, Mark Rutland wrote:
> > > > Are you then going to hack GRUB, release a special HiKey version of
> > > > GRUB, not support any other versions, and still can your firmware
> > > > UEFI?
> > > 
> > > I don't need to hack GRUB at all.
> > 
> > Then it is working for you by pure chance alone.
> > 
> > Please listen to the advice you are being given here; we're trying to
> > ensure that your platform functions (and continues to function) as best
> > it can.
> 
> Since we discussed a lot on this, let's make a conclusion on it.
> 
> 1. UEFI could append the reserved buffer in it's memory mapping.
> 2. These reserved buffer must be declared in DT, since we also need to
>    support non-UEFI (uboot) at the same time.
> 3. Mailbox node should reference reserved buffer by phandle in DT. Then
>    map the buffer as non-cacheable in driver.
> 4. These reserved buffer must use "no-map" property since it should be
>    non-cacheable in driver.

For more specific discussion for DTS, i list two options at here;

- Option 1: just simply reserve memory regions through memory node,
  and mailbox node will directly use the buffer through reg ranges;

- Option 2: use reserved-memory and mailbox node will refer phandle
  of reserved-memory;

These two options both can work well with UEFI and Uboot, but option 1
is more simple and straightforward; so i personally prefer it. But
look forwarding your guys' suggestion.

Option 1:

	memory@0 {
		device_type = "memory";
		reg = <0x00000000 0x00000000 0x00000000 0x05e00000>,
		      <0x00000000 0x05f00000 0x00000000 0x00eff000>,
		      <0x00000000 0x06e00000 0x00000000 0x0060f000>,
		      <0x00000000 0x07410000 0x00000000 0x38bf0000>;
	};

        [...]

	mailbox: mailbox@...10000 {
		#mbox-cells = <1>;
		compatible = "hisilicon,hi6220-mbox";
		reg = <0x0 0xf7510000 0x0 0x1000>, /* IPC_S */
		      <0x0 0x06dff800 0x0 0x0800>; /* Mailbox buffer */
		interrupts = <GIC_SPI 94 IRQ_TYPE_LEVEL_HIGH>;
	};

Option 2:

	memory@0 {
		device_type = "memory";
		reg = <0x0 0x0 0x0 0x40000000>;
	};

	reserved-memory {
		#address-cells = <2>;
		#size-cells = <2>;
		ranges;

		mcu_reserved: mcu_reserved@...ff000 {
			no-map;
			reg = <0x0 0x06dff000 0x0 0x00001000>,	/* MCU mailbox buffer */
			      <0x0 0x05e00000 0x0 0x00100000>,	/* MCU firmware buffer */
			      <0x0 0x0740f000 0x0 0x00001000>;	/* MCU firmware section */
		};
	};

        [...]

	mailbox: mailbox@...10000 {
		#mbox-cells = <1>;
		compatible = "hisilicon,hi6220-mbox";
		reg = <0x0 0xf7510000 0x0 0x1000>; /* IPC_S */
		memory-region = <&mcu_reserved>;   /* Mailbox buffer */
		interrupts = <GIC_SPI 94 IRQ_TYPE_LEVEL_HIGH>;
	};


> 5. A patch is necessary in kernel. If efi stub feature is enabled,
>    arm kernel should not parse memory node or reserved memory buffer in
>    DT any more. Arm kernel should either fetch memory information from 
>    efi or DT. Currently arm kernel fetch both efi memory information and
>    reserved buffer from DTB at the same time.
> 
> Do you agree on these points?
> 
> Regards
> Haojian
> 
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