linux-kernel - Re: [PATCH v2 03/12] bus: stm32-fmc2-ebi: add STM32 FMC2 EBI controller driver

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Date:   Fri, 17 Apr 2020 17:31:49 +0200
From:   Marek Vasut <marex@...x.de>
To:     Christophe Kerello <christophe.kerello@...com>,
        Boris Brezillon <boris.brezillon@...labora.com>
Cc:     miquel.raynal@...tlin.com, richard@....at, vigneshr@...com,
        lee.jones@...aro.org, robh+dt@...nel.org, mark.rutland@....com,
        tony@...mide.com, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-mtd@...ts.infradead.org,
        linux-stm32@...md-mailman.stormreply.com
Subject: Re: [PATCH v2 03/12] bus: stm32-fmc2-ebi: add STM32 FMC2 EBI
 controller driver

On 4/17/20 5:29 PM, Christophe Kerello wrote:
> 
> 
> On 4/16/20 9:53 PM, Boris Brezillon wrote:
>> On Wed, 15 Apr 2020 17:57:27 +0200
>> Christophe Kerello <christophe.kerello@...com> wrote:
>>
>>> The driver adds the support for the STMicroelectronics FMC2 EBI
>>> controller
>>> found on STM32MP SOCs.
>>>
>>> Signed-off-by: Christophe Kerello <christophe.kerello@...com>
>>> Tested-by: Marek Vasut <marex@...x.de>
>>> ---
>>> Changes in v2:
>>>   - call 2 APIs to manage FMC2 enable/disable instead of ops
>>>   - call 2 APIs to manage FMC2 NWAIT shared signal instead of ops
>>>
>>>   drivers/bus/Kconfig          |   11 +
>>>   drivers/bus/Makefile         |    1 +
>>>   drivers/bus/stm32-fmc2-ebi.c | 1091
>>> ++++++++++++++++++++++++++++++++++++++++++
>>
>> Hm, I see that other memory bus controller drivers are placed under
>> drivers/memory/, any reason for choosing drivers/bus/? If that's where
>> we want to have all generic memory bus controllers to live it might be
>> worth moving existing drivers to the drivers/bus/ directory at some
>> point.
>>
> 
> Hi Boris,
> 
> I see this controller as an external bus interface as we are able to
> attach different devices on it, like a PSRAM, an ethernet controller, a
> FPGA, a LCD display, ...
> 
> When I had a look at bus/Kconfig file, I have found similar drivers
> (like IMX_WEIM or QCOM_EBI2 drivers). These drivers are able to connect
> devices like NAND Flash, SRAM, ethernet adapters, FPGAs and LCD displays
> as it is written in the Kconfig file.
> 
> But, after checking memory/Kconfig file, it is also possible to find
> similar drivers (like ATMEL_EBI driver that is inspired by the WEIM bus
> driver).
> 
> So, I will follow the recommendation and I will move it to
> drivers/memory folder if it is the place where this driver should be.

The EBI isn't a memory bus, you can very well have a non-memory device,
like an external parallel bus memory controller on it. So why should it
be in drivers/memory ?