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Date: Wed, 25 Nov 2015 01:54:16 +0900
From: Masahiro Yamada <yamada.masahiro@...ionext.com>
To: Mark Rutland <mark.rutland@....com>
Cc: devicetree@...r.kernel.org, Pawel Moll <pawel.moll@....com>,
Ian Campbell <ijc+devicetree@...lion.org.uk>,
Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
Rob Herring <robh+dt@...nel.org>, arm@...nel.org,
Kumar Gala <galak@...eaurora.org>,
linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH 1/4] bus: uniphier-system-bus: add UniPhier System Bus
Controller driver
Hi Mark,
2015-11-24 20:50 GMT+09:00 Mark Rutland <mark.rutland@....com>:
> On Tue, Nov 24, 2015 at 06:39:19PM +0900, Masahiro Yamada wrote:
>> The UniPhier System Bus is an external bus where on-board devices are
>> connected to the UniPhier SoC. This driver parses the "ranges"
>> property of the System Bus and set up the registers of the System Bus
>> Controller for the correct bus routing.
>
> Could you elaborate on why you need to do that?
In order to have access to the System Bus (external bus),
the System Bus Controller must be set up.
> What needs to be configured specifically?
The base address and the size of each bank (each chip select)
must be set to the registers of the controller.
> [...]
>
>> +The UniPhier System Bus is an external bus where on-board devices are connected
>> +to the UniPhier SoC. It it a simple parallel bus with address, data, and some
>> +control signals. It supports up to 8 banks (chip selects).
>> +
>> +Required properties for System Bus:
>> +- compatible: should be "socionext,uniphier-system-bus", "simple-bus".
>
> If the kernel has to perform setup of the bus, then it is not a
> "simple-bus".
>
> Configure the bus, then probe children. Don't use simple-bus jsut to get
> probing.
OK, I will fix in v2.
>> +- #address-cells: should be equal to or grater than 2. The first cell is the
>
> s/grater/greater/
OK, thanks.
>> + bank number (chip select). The rest is the base address within the bank that
>> + should be mapped onto the parent bus (usually AMBA).
>> +
>> +Optional properties for System Bus:
>> +- #size-cells: should be the same as that of the parent bus, if exists. The
>> + value of the parent bus is assumed, if not specified.
>
> This should be just as required as #address-cells, for consistency.
Will fix.
>> +
>> +
>> +UniPhier System Bus Controller
>> +------------------------------
>> +
>> +The UniPhier System Bus Controller is a hardware block with registers that
>> +controls the System Bus accessing; how each bank is mapped onto the parent bus,
>> +various timing parameters of the bus access, etc.
>> +
>> +Required properties for System Bus Controller:
>> +- compatible: should be "socionext,uniphier-system-bus-controller".
>> +- reg: offsets and lengths of the register sets for the device. It should
>> + contain 2 regions: base & control register, misc register, in this order.
>
> The example also has a system-bus phandle.
Actually, I was wondering which is better to describe the relation between
the bus and the controller, phandle or compatible string..
> Is the "misc register" part of the bus controller, or is it a shared
> system controller?
It is a part of the bus controller, but used for another purpose.
(i.e. partly this is syscon. I know this is strange, but it is
what the hardware developers designed.)
>> +Example
>> +-------
>> + system_bus: system-bus {
>> + compatible = "socionext,uniphier-system-bus", "simple-bus";
>> + #address-cells = <2>;
>> + #size-cells = <1>;
>> + ranges = <1 0x00000000 0x42000000 0x02000000
>> + 5 0x00000000 0x48000000 0x01000000>;
>> +
>> + eth: ethernet@1,01f00000 {
>> + compatible = "smsc,lan9115";
>> + reg = <1 0x01f00000 0x1000>;
>> + phy-mode = "mii";
>> + reg-io-width = <4>;
>> + };
>> +
>> + serial: uart@5,00200000 {
>> + compatible = "ns16550a";
>> + reg = <5 0x00200000 0x20>;
>> + clock-frequency = <12288000>;
>> + reg-shift = <1>;
>> + };
>> + };
>> +
>> + system-bus-controller@...00000 {
>> + compatible = "socionext,uniphier-system-bus-controller";
>> + reg = <0x58c00000 0x400>, <0x59800000 0x2000>;
>> + system-bus = <&system_bus>;
>> + };
>
> Assuming that the controller and bus are 1-1 related, make this a single
> node. e.g.
>
> system-bus {
> compatible = "socionext,uniphier-system-bus";
> reg = <0x58c00000 0x400>, <0x59800000 0x2000>;
> #address-cells = <2>;
> #size-cells = <1>;
> ranges = <1 0x00000000 0x42000000 0x02000000>,
> <5 0x00000000 0x48000000 0x01000000>;
>
> ...
> child nodes here
> ...
>
> };
Hmm, make sense. But, I prefer to reflect the hardware structure.
The range of System Bus is <0x40000000 0x10000000>.
The register of the System Bus Controller is
<0x58c00000 0x400> (and <0x59800000 0x2000>)
The bus and its controller is different.
> [...]
>
>> +static int uniphier_sbc_probe(struct platform_device *pdev)
>> +{
>> + struct device *dev = &pdev->dev;
>> + struct uniphier_sbc_priv *priv;
>> + struct resource *regs;
>> + struct device_node *bus_np;
>> + int child_addrc, addrc, sizec, bank;
>> + u64 child_addr, addr, size;
>> + const __be32 *ranges;
>> + int rlen, rone, ret;
>> +
>> + bus_np = of_find_compatible_node(NULL, NULL,
>> + "socionext,uniphier-system-bus");
>
> This is broken if you ever have multiple instances.
>
> Either use a single node, or if there is a more complex relationship
> between busses and their controllers, describe that explicitly with
> phandles.
Probably, I will stick to phandle in v2.
Thanks,
--
Best Regards
Masahiro Yamada
--
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