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Date: Thu, 21 Mar 2024 17:25:09 +0530
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Subject: Re: [PATCH v4 1/5] dt-bindings: misc: Add mikrobus-connector
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To: Michael Walle <mwalle@kernel.org>, Andrew Lunn <andrew@lunn.ch>
CC: "Russell King (Oracle)" <linux@armlinux.org.uk>,
        Ayush Singh
	<ayushdevel1325@gmail.com>,
        open list <linux-kernel@vger.kernel.org>, <jkridner@beagleboard.org>,
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        Krzysztof
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        Vaishnav M A <vaishnav@beagleboard.org>
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From: Vaishnav Achath <vaishnav.a@ti.com>
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On 21/03/24 15:08, Michael Walle wrote:
> Hi,
> 
>>> Is that because the current software support is too limited? Are there
>>> manufactures who want to create more complex designed, but are limited
>>> by what can be described in the manifest?
>>>
>>
>> most mikroBUS add-on boards in production lies in the category of
>> sensors, displays, connectivity, mixed signal (ADC/DAC .etc) and if you
>> look at the existing bindings under bindings/iio/ , most devices need
>> only simple descriptions and the properties are mainly standard bus
>> properties (SPI/I2C properties), IRQ, named-gpios, named properties,
>> regulators, clocks the extension to manifest was made taking this into
>> account and the named property description interface just maps the
>> manifest entries to the unified device property interface under
>> include/linux/property.h
> 
> How will the ethernet boards ([1], [2]) work? Where do they get
> their MAC address from, for example. The DT has some nice properties
> for that, but I doubt that will be possible with the manifest files.
> I've looked at the manifest file for the w5500 board [3] and to me
> it looks like that board will come up with a random MAC address on
> each start. Thus, even today, you have some boards which require
> a more complex description.
> 

Agreed, this is a limitation, unless the corresponding 
drivers/subsystems use device_property_read_* helper to fetch 
properties, it will not work and net/core/of_net.c only implements 
of_get_* helpers even though the underlying functions can be implemented 
with equivalent device_property_read_* equivalent as well.

> Apart from the discussion whether the manifest is a suitable or
> sufficient mechanism to describe the hardware, I think the main
> problem with the proposed binding, is that it doesn't follow the
> binding Rob was proposing for a socket. If I want to use DT
> overlays, how would you describe an add-on board?
> 
> The proposal was that the base board has something like
> 
> mikrobus: socket {
> 	compatible = "mikrobus-socket";
> 	i2c-parent = <&i2c0>;
> 	spi-parent = <&spi0>;
> 
> 	i2c {};
> 	spi {};
> };
> 
> an add-on board can then have a DT snippet/overlay like the
> following:
> 
> &mikrobus {
> 	i2c {
> 		eeprom@52: {
> 			reg = <52>;
> 			compatible = <atmel,at24..>;
> 		}
> 	};
> 
> 	spi {
> 		sensor@0: {
> 			reg = <0>;
> 			compatible = <foobar>;
> 		};
> 	};
> };
> 
> That should be possible with a binding for the mikrobus, which
> in fact it is just a pin header with a standard pinout. Also as
> Russell pointed out in v3, the EEPROM/manifest is not part of the
> mikrobus standard. So maybe that deserves an own compatible, like
> 
>     compatible = "mikroe,click", "mikrobus-socket";
> 
> Or maybe click-eeprom? Although click seems to be the brand name of
> MikroElektronika.

Agreed, there is nothing preventing us to convert the binding and update 
the driver to follow the above proposed format and will be done in next 
revision. Click is brand name of MikroElektronika and they don't allow 
custom boards to use that branding, however clickid can be used in the 
case where EEPROM is present/enable the socket to be probeable.

Thanks and Regards,
Vaishnav

> 
> -michael
> 
> [1] https://www.mikroe.com/eth-3-click
> [2] https://www.mikroe.com/eth-wiz-click
> [3] https://github.com/MikroElektronika/click_id/blob/main/manifests/ETH-WIZ-CLICK.mnfs