linux-kernel - Re: [PATCH v6] SATA: OCTEON: support SATA on OCTEON platform

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Date:	Wed, 3 Feb 2016 14:44:32 +0000
From:	Zubair Lutfullah Kakakhel <Zubair.Kakakhel@...tec.com>
To:	Arnd Bergmann <arnd@...db.de>
CC:	<tj@...nel.org>, <hdegoede@...hat.com>, <david.daney@...ium.com>,
	<aleksey.makarov@...iumnetworks.com>, <devicetree@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>, <linux-ide@...r.kernel.org>
Subject: Re: [PATCH v6] SATA: OCTEON: support SATA on OCTEON platform

Hi,

On 03/02/16 13:47, Arnd Bergmann wrote:
> On Wednesday 03 February 2016 13:24:10 Zubair Lutfullah Kakakhel wrote:
>>> Typically we treat those special registers as part of the device itself
>>> and have a single device node for the AHCI controller and that one.
>>>
>>> What is your reason for doing it differently here?
>>
>> Two reasons
>>
>> 1- The hardware is like a proper split rather than additional hidden registers in
>> the same memory space.
>>
>> 2- Tons of devices in the field have the following DT node built in the bootloader.
>>
>>                  uctl@...006c000000 {
>>                          compatible = "cavium,octeon-7130-sata-uctl";
>>                          reg = <0x11800 0x6c000000 0x0 0x100>;
>>                          ...
>>                           sata: sata@...0000000000 {
>>                                   compatible = "cavium,octeon-7130-ahci";
>>                                   reg = <0x16c00 0x00000000 0x0 0x200>;
>>                                  ...
>>                           };
>>                  };
>>
>> The patch suggests a way to handle this.
>>
>
> Ok, fair enough. Also, you write in the binding that this is a bus
> bridge, so this indeed matches what the hardware does, and that's ok.

Thank-you.

>
> Does the bus bridge actually translate the entire 64-bit CPU MMIO space,
> or is it possible that it only handles one device (or a couple of
> them) with a fairly limited space?

This uctl is just for SATA devices.

>
> Maybe it's better to represent it as a #address-cells=<1> in the
> example, and have the child device appear at address 0 in there.

Possible in the example.

I'll update the example to

	uctl@...006c000000 {
		compatible = "cavium,octeon-7130-sata-uctl";
		reg = <0x11800 0x6c000000 0x0 0x100>;
		ranges; /* Direct mapping */
		dma-ranges;
		#address-cells = <1>;
		#size-cells = <2>;

		sata: sata@0 {
			compatible = "cavium,octeon-7130-ahci";
			reg = <0x16c00 0x00000000 0x0 0x200>;
			interrupt-parent = <&cibsata>;
			interrupts = <2 4>; /* Bit: 2, level */
		};
	};

>
> For the machines that already ship a DT, that would not matter though,
> it works either way.
>
> 	Arnd
>