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SubjectRe: [PATCH v3 3/3] PCI: imx6: Add support for i.MX8MQ
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On 12/20/2018 3:22 AM, Trent Piepho wrote:
> On Wed, 2018-12-19 at 16:47 -0800, Andrey Smirnov wrote:

>>>> This series initially added explicit offsets but I suggested a single
>>>> "controller-id" because:
>>>> * There are multiple bit and byte offsets
>>>> * Other imx8 SOCs also have 2x pcie with other bit/byte offsets
>>>>
>>>> Hiding this behind a compatible string and single "controller-id" seem
>>>> preferable to elaborating register maps in dt bindings. It also makes
>>>> upgrades simpler: if features are added which use other bits there is no
>>>> need to describe them in DT and deal with compatibility headaches.
>>>
>>> You already have an id for the controllers: the address. Use that if
>>> you don't want to put the register offsets in DT.
>>
>> Lucas, are you on board with this?
>
> Does address here mean the address from the controller's reg property?
>
> How do you map that address to the controller's index?

I guess you could have a constant for the address of the first
controller and then substract. But hardcoding any sort of physical
address feels wrong with DT.
> The situation here is that some registers for these controllers are
> interleaved, right? I.e., there's one register somewhere where bit 0
> means enable controller 0 and bit 1 means enable controller 1 and so
> on.
>
> Isn't cell-index already the standard device tree property for this
> kind of setup?

Look at how this cell-index property is documented in other bindings it
seems to be an excellent fit: just rename controller-id to cell-index.

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