linux-kernel - Re: [PATCH 1/2] mfd: core: Support multiple OF child devices of the same type

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Date:   Thu, 6 Jun 2019 06:27:00 +0100
From:   Lee Jones <lee.jones@...aro.org>
To:     Robert Hancock <hancock@...systems.ca>
Cc:     linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] mfd: core: Support multiple OF child devices of the
 same type

On Wed, 05 Jun 2019, Robert Hancock wrote:

> On 2019-06-05 12:45 p.m., Lee Jones wrote:
> >>>> diff --git a/include/linux/mfd/core.h b/include/linux/mfd/core.h
> >>>> index 99c0395..470f6cb 100644
> >>>> --- a/include/linux/mfd/core.h
> >>>> +++ b/include/linux/mfd/core.h
> >>>> @@ -55,6 +55,9 @@ struct mfd_cell {
> >>>>  	 */
> >>>>  	const char		*of_compatible;
> >>>>  
> >>>> +	/* Optionally match against a specific device of a given type */
> >>>> +	const char		*of_full_name;
> >>>> +
> >>>
> >>> Can you give me an example for when this might be useful?
> >>
> >> This is an example of some device tree entries for our MFD device:
> >>
> >>             axi_iic_0: i2c@...00 {
> >>                 compatible = "xlnx,xps-iic-2.00.a";
> >>                 clocks = <&axi_clk>;
> >>                 clock-frequency = <100000>;
> >>                 interrupts = <7>;
> >>                 #size-cells = <0>;
> >>                 #address-cells = <1>;
> >>             };
> >>
> >>             axi_iic_1: i2c@...00 {
> >>                 compatible = "xlnx,xps-iic-2.00.a";
> >>                 clocks = <&axi_clk>;
> >>                 clock-frequency = <100000>;
> >>                 interrupts = <8>;
> >>                 #size-cells = <0>;
> >>                 #address-cells = <1>;
> >>             };
> >>
> >> and the corresponding MFD cells:
> >>
> >> {
> >> 	.name		= "axi_iic_0",
> >> 	.of_compatible	= "xlnx,xps-iic-2.00.a",
> >> 	.of_full_name	= "i2c@...00",
> >> 	.num_resources	= ARRAY_SIZE(dbe_i2c1_resources),
> >> 	.resources	= dbe_i2c1_resources
> >> },
> >> {
> >> 	.name		= "axi_iic_1",
> >> 	.of_compatible	= "xlnx,xps-iic-2.00.a",
> >> 	.of_full_name	= "i2c@...00",
> >> 	.num_resources	= ARRAY_SIZE(dbe_i2c2_resources),
> >> 	.resources	= dbe_i2c2_resources
> >> },
> >>
> >> Without having the .of_full_name support, both MFD cells ended up
> >> wrongly matching against the i2c@...00 device tree node since we just
> >> picked the first one where of_compatible matched.
> > 
> > What is contained in each of their resources?
> 
> These are the resource entries for those two devices:
> 
> static const struct resource dbe_i2c1_resources[] = {
> {
> 	.start		= 0xc0000,
> 	.end		= 0xcffff,
> 	.name		= "xi2c1_regs",
> 	.flags		= IORESOURCE_MEM,
> 	.desc		= IORES_DESC_NONE
> },
> };
> 
> static const struct resource dbe_i2c2_resources[] = {
> {
> 	.start		= 0xd0000,
> 	.end		= 0xdffff,
> 	.name		= "xi2c2_regs",
> 	.flags		= IORESOURCE_MEM,
> 	.desc		= IORES_DESC_NONE
> },
> };

This is your problem.  You are providing the memory resources through
*both* DT and MFD.  I don't believe I've seen your MFD driver, but it
looks like it's probably not required at all.  Just allow DT to probe
each of your child devices.  You can obtain the IO memory from there
directly using the usual platform_get_resource() calls.

> Ideally the IO memory resource entries would be picked up and mapped
> through the device tree as well, as they are with the interrupts, but I
> haven't yet found the device tree magic that would allow that to happen
> yet, if it's possible. The setup we have has a number of peripherals on
> an AXI bus which are behind a PCIe to AXI bridge, and we're using mfd to
> instantiate each of those AXI devices under the PCIe device.
> 

-- 
Lee Jones [李琼斯]
Linaro Services Technical Lead
Linaro.org │ Open source software for ARM SoCs
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