Re: pci-exynos.c phy_init() usage

Krzysztof Kozlowski
2022-06-28T08:28:56Z

On 28/06/2022 10:13, Marek Szyprowski wrote:
> Hi Krzysztof,
>
> On 27.06.2022 12:47, Krzysztof Kozlowski wrote:
>> On 27/06/2022 12:30, Marek Szyprowski wrote:
>>> On 24.06.2022 20:07, Krzysztof Kozlowski wrote:
>>>> On 24/06/2022 19:35, Bjorn Helgaas wrote:
>>>>> In exynos_pcie_host_init() [1], we call:
>>>>>
>>>>> phy_reset(ep->phy);
>>>>> phy_power_on(ep->phy);
>>>>> phy_init(ep->phy);
>>>>>
>>>>> The phy_init() function comment [2] says it must be called before
>>>>> phy_power_on(). Is exynos doing this backwards?
>>>> Looks like. I don't have Exynos hardware with a PCI, so cannot
>>>> test/fix/verify.
>>>>
>>>> Luckily for Exynos ;-) it's not alone in this pattern:
>>>> drivers/net/ethernet/marvell/sky2.c
>>>> drivers/usb/dwc2/platform.c
>>> I've checked that on the real hardware. Swapping the order of
>>> phy_power_on and phy_init breaks driver operation.
>>>
>>> However pci-exynos is the only driver that uses the phy-exynos-pcie, so
>>> we can simply swap the content of the init and power_on in the phy
>>> driver to adjust the code to the right order. power_on/init and
>>> exit/power_off are also called one after the other in pci-exynos,
>>> without any activity between them, so we can also simply move all
>>> operation to one pair of the callback, like power_on/off.
>>>
>>> Krzysztof, which solution would you prefer?
>> I think the real problem is that the Exynos PCIe phy init
>> (exynos5433_pcie_phy_init) performs parts of power on procedure, so the
>> code is mixed. Probably also the phy init could not happen earlier due
>> to gated clocks (ungated in exynos5433_pcie_phy_power_on).
>>
>> I would prefer to clean it up while ordering init+power_on, so figure
>> out more or less correct procedure.
>>
>> You can also look at Artpec-8 PHY - it seems using correct order
>> (init+reset):
>> https://lore.kernel.org/all/20220614011616epcms2p7dcaa67c53b7df5802dd7a697e2d472d7@epcms2p7/
>
> I've played a bit with those register writes in exynos_pcie_phy and
> frankly speaking the currenly used (power_on + init) is the only
> sequence that works properly. I'm leaning to move everything to
> phy_init/exit. I really don't see how to split it into init + power_on
> callbacks.

I was afraid it will be like this. I imagine that certain (not
explicitly documented) init operations cannot even happen before power
on, so this would be a lot of tries.

I am fine with it. Thanks for doing it.

>
> While touching this - I would also remove the phy_reset() call in the
> exynos-pcie driver. It is a left over from the old, obsoleted exynos5440
> pcie code, not implemented in the current phy driver, also only a few
> drivers use or implement it. IMHO it doesn't make sense to keep such
> dead code.

Sure, looks ok.

Best regards,
Krzysztof