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Subject: Re: [PATCH v2 02/12] mfd: stm32-fmc2: add STM32 FMC2 controller
 driver
To:     Boris Brezillon <boris.brezillon@collabora.com>
CC:     Marek Vasut <marex@denx.de>, Lee Jones <lee.jones@linaro.org>,
        <mark.rutland@arm.com>, <devicetree@vger.kernel.org>,
        <vigneshr@ti.com>, <tony@atomide.com>, <richard@nod.at>,
        <linux-kernel@vger.kernel.org>, <robh+dt@kernel.org>,
        <linux-mtd@lists.infradead.org>, <miquel.raynal@bootlin.com>,
        Geert Uytterhoeven <geert@linux-m68k.org>,
        <linux-stm32@st-md-mailman.stormreply.com>
References: <1586966256-29548-1-git-send-email-christophe.kerello@st.com>
 <1586966256-29548-3-git-send-email-christophe.kerello@st.com>
 <20200424074517.GN3612@dell> <8b625f1c-9ded-c07a-a20e-8cd44c1ca46d@denx.de>
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 <20200424171412.5f65ff05@collabora.com>
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 <20200424192222.28efd55f@collabora.com>
From:   Christophe Kerello <christophe.kerello@st.com>
Message-ID: <cc02d1d2-08a8-1f72-f4eb-6eaa7e48e817@st.com>
Date:   Fri, 24 Apr 2020 19:34:07 +0200
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On 4/24/20 7:22 PM, Boris Brezillon wrote:
> On Fri, 24 Apr 2020 18:42:59 +0200
> Christophe Kerello <christophe.kerello@st.com> wrote:
> 
>> On 4/24/20 5:14 PM, Boris Brezillon wrote:
>>> On Fri, 24 Apr 2020 13:47:34 +0200
>>> Christophe Kerello <christophe.kerello@st.com> wrote:
>>>    
>>>> On 4/24/20 1:06 PM, Marek Vasut wrote:
>>>>> On 4/24/20 12:50 PM, Lee Jones wrote:
>>>>>> On Fri, 24 Apr 2020, Marek Vasut wrote:
>>>>>>      
>>>>>>> On 4/24/20 9:45 AM, Lee Jones wrote:
>>>>>>>> On Wed, 15 Apr 2020, Christophe Kerello wrote:
>>>>>>>>      
>>>>>>>>> The driver adds the support for the STMicroelectronics FMC2 controller
>>>>>>>>> found on STM32MP SOCs.
>>>>>>>>>
>>>>>>>>> The FMC2 functional block makes the interface with: synchronous and
>>>>>>>>> asynchronous static memories (such as PSNOR, PSRAM or other
>>>>>>>>> memory-mapped peripherals) and NAND flash memories.
>>>>>>>>>
>>>>>>>>> Signed-off-by: Christophe Kerello <christophe.kerello@st.com>
>>>>>>>>> ---
>>>>>>>>> Changes in v2:
>>>>>>>>>     - remove ops from stm32_fmc2 structure
>>>>>>>>>     - add 2 APIs to manage FMC2 enable/disable
>>>>>>>>>     - add 2 APIs to manage FMC2 NWAIT shared signal
>>>>>>>>>
>>>>>>>>>     drivers/mfd/Kconfig            |  12 +++
>>>>>>>>>     drivers/mfd/Makefile           |   1 +
>>>>>>>>>     drivers/mfd/stm32-fmc2.c       | 136 +++++++++++++++++++++++++
>>>>>>>>>     include/linux/mfd/stm32-fmc2.h | 225 +++++++++++++++++++++++++++++++++++++++++
>>>>>>>>>     4 files changed, 374 insertions(+)
>>>>>>>>>     create mode 100644 drivers/mfd/stm32-fmc2.c
>>>>>>>>>     create mode 100644 include/linux/mfd/stm32-fmc2.h
>>>>>>>>>
>>>>>>>>> diff --git a/drivers/mfd/Kconfig b/drivers/mfd/Kconfig
>>>>>>>>> index 2b20329..5260582 100644
>>>>>>>>> --- a/drivers/mfd/Kconfig
>>>>>>>>> +++ b/drivers/mfd/Kconfig
>>>>>>>>> @@ -1922,6 +1922,18 @@ config MFD_ROHM_BD71828
>>>>>>>>>     	  Also included is a Coulomb counter, a real-time clock (RTC), and
>>>>>>>>>     	  a 32.768 kHz clock gate.
>>>>>>>>>     
>>>>>>>>> +config MFD_STM32_FMC2
>>>>>>>>> +	tristate "Support for FMC2 controllers on STM32MP SoCs"
>>>>>>>>> +	depends on MACH_STM32MP157 || COMPILE_TEST
>>>>>>>>> +	select MFD_CORE
>>>>>>>>> +	select REGMAP
>>>>>>>>> +	select REGMAP_MMIO
>>>>>>>>> +	help
>>>>>>>>> +	  Select this option to enable STM32 FMC2 driver used for FMC2 External
>>>>>>>>> +	  Bus Interface controller and FMC2 NAND flash controller. This driver
>>>>>>>>> +	  provides core support for the STM32 FMC2 controllers, in order to use
>>>>>>>>> +	  the actual functionality of the device other drivers must be enabled.
>>>>>>>>
>>>>>>>> Not sure how many times I have to say this before people stop
>>>>>>>> attempting to pass these kinds of relationships off as MFDs:
>>>>>>>>
>>>>>>>> A memory device and its bus is not an MFD.  In a similar vain to the
>>>>>>>> thousands of USB, I2C, SPI, PCI and the like devices that aren't MFDs
>>>>>>>> either.
>>>>>>>>
>>>>>>>> Please find another way to associate your device with its bus.
>>>>>>>
>>>>>>> This FMC2 is however an IP which can either operate external devices
>>>>>>> (like ethernet chip on this parallel bus) or external flashes (like NOR
>>>>>>> and NAND chips).
>>>>>>
>>>>>> I'm sure that it *can*.  Although that's not its main purpose.
>>>>>
>>>>> I use it to operate KSZ8851-16MLL ethernet chip, which has async bus
>>>>> interface. Linux just didn't have support for that mode of operation
>>>>> thus far and the FMC was used to operate NANDs and NORs only. This
>>>>> series, or rather, the first three patches in this series, add support
>>>>> for operating other bus devices, like this ethernet controller.
>>>>>       
>>>>>> The
>>>>>> clue is in the nomenclature ("Flexible *Memory* Controller").  Nor is
>>>>>> it how the device is being used in this submission:
>>>>>>
>>>>>>      "The FMC2 functional block makes the interface with: synchronous and
>>>>>>       asynchronous static memories (such as PSNOR, PSRAM or other
>>>>>>       memory-mapped peripherals) and NAND flash memories."
>>>>>>
>>>>>> As I mentioned, this is just another memory device and its bus.
>>>>>
>>>>> I don't think it's _just_ a memory controller, it's more universal than
>>>>> that, see above. Note that SRAM interface basically boils down to
>>>>> anything which has external parallel bus, e.g. Davicom DM9000, that
>>>>> KSZ8851-16MLL etc.
>>>>>       
>>>>>>> Can you provide a suggestion how this should be handled, if not as MFD?
>>>>>>> It seems to me, that this is a Multi-Function Device .
>>>>>>
>>>>>> Simply move it into the MTD or Memory subsystems and set up the
>>>>>> dependencies via Kconfig.
>>>>>>      
>>>>>>> If this discussion is a recurring topic, is there some documentation
>>>>>>> which explains how such devices should be handled ?
>>>>>>
>>>>>> Not that I'm aware of.
>>>>>
>>>>> I see.
>>>>>      
>>>>
>>>> Hi Lee, Marek,
>>>>
>>>> I will move this source code in the FMC2 bus driver. I think that I
>>>> should be able to manage the 2 controllers with 2 drivers (the FMC2 bus
>>>> driver and the FMC2 raw NAND driver).
>>>
>>> FWIW, that's what I did for the Atmel EBI (External Bus Interface)
>>> controller (see [1]).
>>>
>>> [1]https://elixir.bootlin.com/linux/v5.6/source/drivers/memory/atmel-ebi.c
>>>    
>>
>> Hi Boris,
>>
>> Thanks for your help.
>>
>> I was thinking about the bindings and I think that the bindings below
>> are close to what has been done for Atmel EBI/Raw NAND bindings (in
>> terms of structure of bindings if I have well understood).
>> I think that these proposed bindings are very close to the first
>> proposed version (V1/V2).
> 
> Yep, makes sense to me, just one minor comment.
> 
>>
>>       fmc@58002000 {
>>         #address-cells = <2>;
>>         #size-cells = <1>;
>>         compatible = "st,stm32mp1-fmc2";
>>         reg = <0x58002000 0x1000>;
>>         clocks = <&rcc FMC_K>;
>>         resets = <&rcc FMC_R>;
>>
>>         ranges = <0 0 0x60000000 0x4000000>, /* EBI bank 1 */
>>                  <1 0 0x64000000 0x4000000>, /* EBI bank 2 */
>>                  <2 0 0x68000000 0x4000000>, /* EBI bank 3 */
>>                  <3 0 0x6c000000 0x4000000>, /* EBI bank 4 */
>>                  <4 0 0x80000000 0x4000000>, /* NAND common memory space */
>>                  <5 0 0x88000000 0x4000000>; /* NAND attribute memory
>> space */
>> 	
>>         psram@0 {
>>           compatible = "mtd-ram";
>>           reg = <0 0x00000000 0x100000>;
>>           bank-width = <2>;
>>
>>           st,fmc2_ebi_cs_transaction_type = <1>;
>>           st,fmc2_ebi_cs_address_setup = <60>;
>>           st,fmc2_ebi_cs_data_setup = <30>;
>>           st,fmc2_ebi_cs_bus_turnaround = <5>;
> 
> Not sure what the unit is for those timings, but I'd recommend using a
> time unit (nanoseconds?) and not clk-cycles here.
>

Hi Boris,

Yes, it is the case in the documentation. The time unit is nanoseconds:
       st,fmc2_ebi_cs_address_setup:
         description: This property defines the duration of the address
                      setup phase in ns used for asynchronous read/write 
transactions.
         $ref: /schemas/types.yaml#/definitions/uint32

Thanks to have review this proposal.

Regards,
Christophe Kerello.

>>         };
>>
>>         nand-controller@4 {
>>           #address-cells = <1>;
>>           #size-cells = <0>;
>>           compatible = "st,stm32mp15-fmc2";
>>           reg = <4 0x00000000 0x1000>,
>>                 <5 0x00010000 0x1000>,
>>                 <5 0x00020000 0x1000>,
>>                 <4 0x01000000 0x1000>,
>>                 <5 0x01010000 0x1000>,
>>                 <5 0x01020000 0x1000>;
>>           interrupts = <GIC_SPI 48 IRQ_TYPE_LEVEL_HIGH>;
>>           dmas = <&mdma1 20 0x2 0x12000a02 0x0 0x0>,
>>                  <&mdma1 20 0x2 0x12000a08 0x0 0x0>,
>>                  <&mdma1 21 0x2 0x12000a0a 0x0 0x0>;
>>           dma-names = "tx", "rx", "ecc";
>>
>>           nand@0 {
>>             reg = <0>;
>>             nand-on-flash-bbt;
>>             #address-cells = <1>;
>>             #size-cells = <1>;
>>           };
>>         };
>>       };
>>
>> Regards,
>> Christophe Kerello.
>>
>