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

[Masahiro Yamada]

Hi Marek,


2016-12-05 12:44 GMT+09:00 Marek Vasut <marek.vasut@xxxxxxxxx>:
> On 12/05/2016 04:30 AM, Masahiro Yamada wrote:
>> Hi Dinh,
>>
>>
>> 2016-12-04 7:08 GMT+09:00 Dinh Nguyen <dinh.linux@xxxxxxxxx>:
>>> Hi,
>>>
>>> On Fri, Dec 2, 2016 at 8:49 PM, Marek Vasut <marek.vasut@xxxxxxxxx> 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@xxxxxxxxxx>:
>>>>>
>>>>>>>
>>>>>>>
>>>>>>> (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@xxxxxxxxxx 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?
Removing "denali,denali-nand-dt" is not breakage at all,
so I do not owe anything to them, right?



-- 
Best Regards
Masahiro Yamada