Re: [PATCH 39/39] mtd: nand: denali_dt: add compatible strings for UniPhier SoC variants

[Marek Vasut <marek.vasut@gmail.com>]

On 12/05/2016 09:51 PM, Dinh Nguyen wrote:
> On Sun, Dec 4, 2016 at 10:22 PM, Marek Vasut <marek.vasut@gmail.com> wrote:
>> On 12/05/2016 05:10 AM, Masahiro Yamada wrote:
>>> Hi Marek,
>>>
>>>
>>> 2016-12-05 12:44 GMT+09:00 Marek Vasut <marek.vasut@gmail.com>:
>>>> On 12/05/2016 04:30 AM, Masahiro Yamada wrote:
>>>>> Hi Dinh,
>>>>>
>>>>>
>>>>> 2016-12-04 7:08 GMT+09:00 Dinh Nguyen <dinh.linux@gmail.com>:
>>>>>> Hi,
>>>>>>
>>>>>> On Fri, Dec 2, 2016 at 8:49 PM, Marek Vasut <marek.vasut@gmail.com> wrote:
>>>>>>> On 12/03/2016 03:41 AM, Masahiro Yamada wrote:
>>>>>>>> Hi Rob,
>>>>>>>
>>>>>>> Hi!
>>>>>>>
>>>>>>>> 2016-12-03 1:26 GMT+09:00 Rob Herring <robh@kernel.org>:
>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>> (Plan A)
>>>>>>>>>>   "denali,socfpga-nand"           (for Altera SOCFPGA variant)
>>>>>>>>>>   "denali,uniphier-nand-v1"       (for old Socionext UniPhier family variant)
>>>>>>>>>>   "denali,uniphier-nand-v2"       (for new Socionext UniPhier family variant)
>>>>>>>>>>
>>>>>>>>>> (Plan B)
>>>>>>>>>>   "altera,denali-nand"            (for Altera SOCFPGA variant)
>>>>>>>>>>   "socionext,denali-nand-v5a"     (for old Socionext UniPhier family variant)
>>>>>>>>>>   "socionext,denali-nand-v5b"     (for new Socionext UniPhier family variant)
>>>>>>>>
>>>>>>>>> Let the Altera folks worry about their stuff. At least for soft IP in
>>>>>>>>> FPGA, it's a bit of a special case. The old string can remain as bad
>>>>>>>>> as it is.
>>>>>>>>
>>>>>>>>
>>>>>>>> Hmm, I am not sure if this IP would fit in FPGA
>>>>>>>> (to use it along with NIOS-II?)
>>>>>>>>
>>>>>>>> (even if it happened, nothing of this IP would be customizable on users' side.
>>>>>>>> When buying the IP, SoC vendors submit a list of desired features.
>>>>>>>> Denali (now Cadence) generates the RTL according to the configuration sheet.
>>>>>>>> The function is fixed at this point. So, generic compatible would be
>>>>>>>> useless anyway.)
>>>>>>>>
>>>>>>>>
>>>>>>>> If we are talking about SOCFPGA,
>>>>>>>> SOCFPGA is not only FPGA. Rather "SOC" + "FPGA".
>>>>>>>> It consists of two parts:
>>>>>>>> [1] SOC part  (Cortex-A9 + various hard-wired peripherals such UART,
>>>>>>>> USB, SD, NAND, ...)
>>>>>>>> [2] FPGA part (User design logic)
>>>>>>>>
>>>>>>>> The Denali NAND controller is included in [1].
>>>>>>>> So, as far as we talk about the Denali on SOCFPGA,
>>>>>>>> it is as hard-wired as Intel, Socionext's ones.
>>>>>>>
>>>>>>> That's correct, the Denali NAND IP in altera socfpga is a hardware
>>>>>>> block. You can make it available to the fabric too, but by default
>>>>>>> it's used by the ARM part of the chip, so for this discussion, you
>>>>>>> can forget that the FPGA part exists altogether.
>>>>>>>
>>>>>>> I would be in favor of plan B, since it seems to be the more often
>>>>>>> taken approach. A nice example is ci-hdrc:
>>>>>>>
>>>>>>> $ git grep compatible drivers/usb/chipidea/
>>>>>>>
>>>>>>>>> I simply would do "socionext,uniphier-v5b-nand" (and v5a).
>>>>>>>>> The fact that it is denali is part of the documentation.
>>>>>>>>>
>>>>>>>>
>>>>>>>> Let me think about this.
>>>>>>>>
>>>>>>>> Socionext bought two version of Denali IP,
>>>>>>>> and we are now re-using the newer one (v5b) for several SoCs.
>>>>>>>> Socionext has some more product lines other than Uniphier SoC family,
>>>>>>>> perhaps wider re-use might happen in the future.
>>>>>>>>
>>>>>>>> At first, I included "uniphier" in compatible, but I am still wondering
>>>>>>>> if such a specific string is good or not.
>>>>>>>>
>>>>>>>> Also, comments from Altera engineers are appreciated.
>>>>>>
>>>>>> Sorry, it's taken me a while to add comments. My altera email is very spotty now
>>>>>> that the Intel merge is completed. Please use dinguyen@kernel.org for any future
>>>>>> communications.
>>>>>>
>>>>>> Yes, everything that is said so far for the NAND controller on the
>>>>>> SoCFPGA is correct. I added the binding for the controller a while
>>>>>> back, but unfortunately, we never added the NAND interface to the
>>>>>> devkit, so we did not do much in terms of enabling it.
>>>>>>
>>>>>> I think the only SoCFPGA board I know that has the NAND interface active is
>>>>>> the TRCom board, but I have never seen that board.
>>>>>>
>>>>>> I don't have any strong opinions on this matter, just as long as the
>>>>>> original binding
>>>>>> "denali,denali-nand-dt" is kept, and I think Rob was ok with keeping
>>>>>> that binding.
>>>>>>
>>>>>
>>>>> I am proposing to add "altera,denali-nand" for Altera.
>>>>> For what, do you need the generic compatible?
>>>>> This IP has no default for it to fallback to.
>>>>
>>>> IMO just for compatibility reasons with old DTs .
>>>
>>> We generally contribute for
>>> a "working driver" (at least, should be functional to some extent)
>>> and "DT binding" bundled together.
>>>
>>> However, Altera upstreamed the DT binding first
>>> (then some parts of the DT binding turned out wrong),
>>> but they did not upstream needed driver changes in the end.
>>>
>>> So, the mainline driver has never worked on SOCFPGA, right?
>>
>> Most likely it never worked, yes.
>>
> 
> Right, looking through our downstream support, we may need to upstream a
> few changes to make upstream driver work on SoCFPGA.
> 
>>> Removing "denali,denali-nand-dt" is not breakage at all,
>>> so I do not owe anything to them, right?
>>
>> I don't think I'm really qualified to answer this one. But, there is
>> drivers/mtd/nand/denali_dt.c , which handles this compatible string
>> and it's documented in
>> Documentation/devicetree/bindings/mtd/denali-nand.txt, so doesn't that
>> make it part of the ABI ? I think we should
>> at least keep it as a fallback, that should be pretty harmless.
>>
> 
> I would like to propose "altr,denali-nand" as the binding we use to support the
> driver going forward on SoCFPGA hardware. It's pretty much the same as
> "altera,denali-nand", just with the correct vendor prefix.

Ah right, altr is the right prefix, thanks for pointing that out.
Still, wouldn't altr,socfpga-denali-nand be better ? I know it's
long, but it encodes the chip type , like ie. fsl,imx6q-usb .

> If we can please keep, "denali,denali-nand-dt" only because SoCFPGA is using
> this binding downstream, but I know that is a weak argument.

-- 
Best regards,
Marek Vasut