linux-kernel - Re: [PATCH 3/8] mikrobus: Add mikrobus driver

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Message-ID: <ecd1fff8-9c15-496a-982f-36e6c58e906a@gmail.com>
Date: Wed, 11 Sep 2024 21:32:21 +0530
From: Ayush Singh <ayushdevel1325@...il.com>
To: Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
 Ayush Singh <ayush@...gleboard.org>
Cc: fabien.parent@...aro.org, d-gole@...com, lorforlinux@...gleboard.org,
 jkridner@...gleboard.org, robertcnelson@...gleboard.org,
 Andrew Davis <afd@...com>, Miguel Ojeda <ojeda@...nel.org>,
 Alex Gaynor <alex.gaynor@...il.com>, Boqun Feng <boqun.feng@...il.com>,
 Gary Guo <gary@...yguo.net>, Björn Roy Baron
 <bjorn3_gh@...tonmail.com>, Benno Lossin <benno.lossin@...ton.me>,
 Andreas Hindborg <a.hindborg@...nel.org>, Alice Ryhl <aliceryhl@...gle.com>,
 Trevor Gross <tmgross@...ch.edu>, Rob Herring <robh@...nel.org>,
 Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor Dooley
 <conor+dt@...nel.org>, Derek Kiernan <derek.kiernan@....com>,
 Dragan Cvetic <dragan.cvetic@....com>, Arnd Bergmann <arnd@...db.de>,
 Nishanth Menon <nm@...com>, Vignesh Raghavendra <vigneshr@...com>,
 Tero Kristo <kristo@...nel.org>, linux-kernel@...r.kernel.org,
 rust-for-linux@...r.kernel.org, devicetree@...r.kernel.org,
 linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH 3/8] mikrobus: Add mikrobus driver

On 9/11/24 20:27, Greg Kroah-Hartman wrote:

> On Wed, Sep 11, 2024 at 07:57:20PM +0530, Ayush Singh wrote:
>> A simple platform driver for now that does nothing. This is required
>> because without a platform driver, the mikrobus_gpio0 nexus node cannot
>> be used.
>>
>> In future, this driver will also allow for dynamic board detection using
>> 1-wire eeprom in new mikrobus boards.
>>
>> Signed-off-by: Ayush Singh <ayush@...gleboard.org>
>> ---
>>   MAINTAINERS              |  1 +
>>   drivers/misc/Kconfig     | 17 +++++++++++++++++
>>   drivers/misc/Makefile    |  1 +
>>   drivers/misc/mikrobus.rs | 32 ++++++++++++++++++++++++++++++++
>>   4 files changed, 51 insertions(+)
>>
>> diff --git a/MAINTAINERS b/MAINTAINERS
>> index 0cc27446b18a..d0c18bd7b558 100644
>> --- a/MAINTAINERS
>> +++ b/MAINTAINERS
>> @@ -15433,6 +15433,7 @@ MIKROBUS CONNECTOR
>>   M:	Ayush Singh <ayush@...gleboard.org>
>>   S:	Maintained
>>   F:	Documentation/devicetree/bindings/connector/mikrobus-connector.yaml
>> +F:	drivers/misc/mikrobus.rs
>>   
>>   MIKROTIK CRS3XX 98DX3236 BOARD SUPPORT
>>   M:	Luka Kovacic <luka.kovacic@...tura.hr>
>> diff --git a/drivers/misc/Kconfig b/drivers/misc/Kconfig
>> index 3fe7e2a9bd29..30defb522e98 100644
>> --- a/drivers/misc/Kconfig
>> +++ b/drivers/misc/Kconfig
>> @@ -610,6 +610,23 @@ config MARVELL_CN10K_DPI
>>   	  To compile this driver as a module, choose M here: the module
>>   	  will be called mrvl_cn10k_dpi.
>>   
>> +menuconfig MIKROBUS
>> +	tristate "Module for instantiating devices on mikroBUS ports"
>> +	help
>> +	  This option enables the mikroBUS driver. mikroBUS is an add-on
>> +	  board socket standard that offers maximum expandability with
>> +	  the smallest number of pins. The mikroBUS driver instantiates
>> +	  devices on a mikroBUS port described by identifying data present
>> +	  in an add-on board resident EEPROM, more details on the mikroBUS
>> +	  driver support and discussion can be found in this eLinux wiki :
>> +	  elinux.org/Mikrobus
> So you want to be a bus?  Or just a single driver?  I'm confused, what
> exactly is this supposed to do?
>
> If a bus, great, let's tie into the proper driver core bus code, don't
> "open code" all of that, as that's just going to make things messier and
> harder to work overall in the end.
>
> If a single driver, why is it called "bus"?  :)
>
> thanks,
>
> greg k-h


Well, mikroBUS [0] is the name of the socket standard. It is basically a 
group of following pins:

Analog - AN
Reset - RST
SPI Chip Select - CS
SPI Clock - SCK
SPI Master Input Slave Output - MISO
SPI Master Output Slave Input - MOSI
VCC-3.3V power - +3.3V
Reference Ground - GND
PWM - PWM output
INT - Hardware Interrupt
RX - UART Receive
TX - UART Transmit
SCL - I2C Clock
SDA - I2C Data
+5V - VCC-5V power
GND - Reference Ground


I do not think it would qualify as as a "bus" in the Linux driver sense. 
Especially with the devicetree based approach here which applies overlay 
directly to the actual uart/i2c/spi controllers and basically not 
interact with the mikroBUS node much.


The driver is here to enable the following:

1. Enable dynamic board detection using 1-wire eeprom on some addon boards.

2. Provide sysfs entry for runtime board adding/removal

3. Enable using mikrobus connector node as nexus node for GPIO (not 
having a platform driver makes any driver trying to use the connector as 
nexus node go into deffered probing state).


For this patch series, the driver is mostly here due to point 3. 
Basically a stub.


[0]: https://www.mikroe.com/mikrobus

Ayush Singh