Re: [PATCH] pinctrl: msm: Add support for MSM TLMM pinmux

From: Stephen Warren
Date: Wed Aug 07 2013 - 12:00:24 EST

On 08/06/2013 05:45 PM, Hanumant Singh wrote:
> On 7/31/2013 5:17 PM, Hanumant Singh wrote:
>> On 7/31/2013 2:06 PM, Stephen Warren wrote:
>>> On 07/31/2013 01:46 PM, Hanumant Singh wrote:
>>>> On 7/30/2013 8:59 PM, Stephen Warren wrote:
>>>>> On 07/30/2013 06:13 PM, Hanumant Singh wrote:
>>>>>> On 7/30/2013 5:08 PM, Stephen Warren wrote:
>>>>>>> On 07/30/2013 06:01 PM, Hanumant Singh wrote:
>>>>>>>> On 7/30/2013 2:22 PM, Stephen Warren wrote:
>>>>>>>>> On 07/30/2013 03:10 PM, hanumant wrote:
>>>>>>>>> ...
>>>>>>>>>> We actually have the same TLMM pinmux used by several socs of a
>>>>>>>>>> family.
>>>>>>>>>> The number of pins on each soc may vary.
>>>>>>>>>> Also a given soc gets used in a number of boards.
>>>>>>>>>> The device tree for a given soc is split into the different
>>>>>>>>>> boards
>>>>>>>>>> that
>>>>>>>>>> its in ie the boards inherit a common soc.dtsi but have separate
>>>>>>>>>> dts.
>>>>>>>>>> The boards for the same soc may use different pin groups for
>>>>>>>>>> accomplishing a function, since we have multiple i2c, spi uart
>>>>>>>>>> etc
>>>>>>>>>> peripheral instances on a soc. A different instance of each of
>>>>>>>>>> the
>>>>>>>>>> above
>>>>>>>>>> peripherals, can be used in different boards, utilizing different
>>>>>>>>>> or subset of same pin groups.
>>>>>>>>>> Thus I would need to have multiple C files for one soc, based
>>>>>>>>>> on the
>>>>>>>>>> boards that it goes into.
>>>>>>>>> The pinctrl driver should be exposing the raw capabilities of
>>>>>>>>> the HW.
>>>>>>>>> All the board-specific configuration should be expressed in DT.
>>>>>>>>> So, the
>>>>>>>>> driver shouldn't have to know anything about different boards at
>>>>>>>>> compile-time.
>>>>>>>> I agree, so I wanted to keep the pin grouping information in DT, we
>>>>>>>> already have a board based differentiation of dts files in DT,
>>>>>>>> for the
>>>>>>>> same soc.
>>>>>>> That's the opposite of what I was saying. Pin groups are a
>>>>>>> feature of
>>>>>>> the SoC design, not the board.
>>>>>> Sorry I guess I wasn't clear.
>>>>>> Right now I have a soc-pinctrl.dtsi containing pin groupings.
>>>>>> This will be "inherited" by soc-boardtype.dts.
>>>>>> The pinctrl client device nodes in soc-boardtype.dts will point to
>>>>>> pin
>>>>>> groupings in soc-pinctrl.dtsi that are valid for that particular
>>>>>> boardtype.
>>>>>> Is this a valid design?
>>>>> OK, so you have two types of child node inside the pinctrl DT node;
>>>>> some
>>>>> define the pin groups the SoC has (in soc.dtsi) and some define
>>>>> pinctrl
>>>>> states that reference the pin group nodes and are referenced by the
>>>>> client nodes.
>>>>> That's probably fine. However, I'd still question putting the pin
>>>>> group
>>>>> nodes in DT at all; I'm not convinced it's better than just putting
>>>>> those into the driver itself. You end up with the same data tables
>>>>> after
>>>>> parsing the DT anyway.
>>>> Any feedback for the rest of the patch?
>>> I'm certainly waiting for this aspect of the patch to be resolved; I
>>> think it will impact the rest of the patch so much that it's not worth
>>> reviewing until we decide on where to represent the pin groups (some DT
>>> parsing could would be removed if we put the pin group definitions into
>>> the driver, hence wouldn't need to be reviewed, and likewise there's be
>>> some new tables to review).
>> I am trying to look at examples of what you are suggesting.
>> I was looking at the exynos implementation, and just from a brief glance
>> it seems like there too the pin grouping is being specified in the
>> device tree, using what looks like labels of the pins.
>> The labels are matched to group structures in soc specific files?
>> By having the pin groupings in DT I am able to reuse the driver without
>> any SOC based code bloat.
>> As I mentioned earlier, we have entire families of SOCs using the same
>> TLMM hardware.
>> Its not a guarantee that for a given TLMM version,
>> the pin groupings on that hardware are the same for every SOC that its
>> in. Its infact most likely that I wont be able to use the pin groupings
>> from one SOC to the next even if they both use the same TLMM.
>> It will very quickly lead to a bloat of
>> pinctrl-<msm_soc>.c (containing the pin groupings replicated for each
>> soc)
>> which use TLMM version specific register programming implementation
>> pinctrl-tlmm-<version>.c
>> and the DT parsing and interface to framework (which remains unchanged).
>> pinctrl-msm.c.
>> Thanks
>> Hanumant
> Any comments on this?

No. As I said, I personally want to see all the pingroups defined in the
pinctrl driver. But, if someone else acks/... the patches without it, I
probably won't nack it.
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