Re: [PATCH v5 2/8] dt-bindings: phy: Add bindings for HiKey 970 PCIe PHY

[Manivannan Sadhasivam <mani@kernel.org>]

Hi Mauro,

On Wed, Jul 14, 2021 at 09:14:35AM +0200, Mauro Carvalho Chehab wrote:
> Em Tue, 13 Jul 2021 20:26:49 -0600
> Rob Herring <robh@kernel.org> escreveu:
> 
> > On Tue, Jul 13, 2021 at 08:28:35AM +0200, Mauro Carvalho Chehab wrote:
> 
> > > +  reset-gpios:
> > > +    description: PCI PERST reset GPIOs
> > > +    maxItems: 4  
> > 
> > Hiding the 4 ports in the phy?
> 
> Rob,
> 
> I'm not trying to hide anything.
> 
> There are several differences with regards to how PERST# is handled between
> HiKey 960 and HiKey 970.
> 
> From hardware perspective, you can see the schematics of both boards:
> 
> 	https://github.com/96boards/documentation/raw/master/consumer/hikey/hikey960/hardware-docs/HiKey960_SoC_Reference_Manual.pdf
> 	https://www.96boards.org/documentation/consumer/hikey/hikey970/hardware-docs/files/hikey970-schematics.pdf
> 
> The 960 PHY has the SoC directly connected to a PCIE M.2 slot 
> (model 10130616) without any external bridge chipset. It uses a single 
> GPIO (GPIO 089) for the PERST# signal, connected via a voltage converter
> (from 1.8V to 3.3V).
> 
> 	$ lspci
> 	00:00.0 PCI bridge: Huawei Technologies Co., Ltd. Device 3660 (rev 01)
> 
> The 970 PHY has an external PCI bridge chipset (PLX Technology PEX 8606).
> Besides the bridge, the hardware comes with an Ethernet PCI adapter, a
> M.2 slot and a mini-PCIe connector. Each one with its own PERST# signal,
> mapped to different GPIO pins, and each one using its own voltage
> converter.
> 
> 	$ lspci
> 	00:00.0 PCI bridge: Huawei Technologies Co., Ltd. Device 3670 (rev 01)
> 	01:00.0 PCI bridge: PLX Technology, Inc. PEX 8606 6 Lane, 6 Port PCI Express Gen 2 (5.0 GT/s) Switch (rev ba)
> 	02:01.0 PCI bridge: PLX Technology, Inc. PEX 8606 6 Lane, 6 Port PCI Express Gen 2 (5.0 GT/s) Switch (rev ba)
> 	02:04.0 PCI bridge: PLX Technology, Inc. PEX 8606 6 Lane, 6 Port PCI Express Gen 2 (5.0 GT/s) Switch (rev ba)
> 	02:05.0 PCI bridge: PLX Technology, Inc. PEX 8606 6 Lane, 6 Port PCI Express Gen 2 (5.0 GT/s) Switch (rev ba)
> 	02:07.0 PCI bridge: PLX Technology, Inc. PEX 8606 6 Lane, 6 Port PCI Express Gen 2 (5.0 GT/s) Switch (rev ba)
> 	02:09.0 PCI bridge: PLX Technology, Inc. PEX 8606 6 Lane, 6 Port PCI Express Gen 2 (5.0 GT/s) Switch (rev ba)
> 	06:00.0 Ethernet controller: Realtek Semiconductor Co., Ltd. RTL8111/8168/8411 PCI Express Gigabit Ethernet Controller (rev 07)
> 
> On other words, there are 4 GPIOs mapped to different PERST# pins in
> the hardware:
> 
> - GPIO 56 is connected to the PERST# pin at PEX 8606;
> - GPIO 25 is connected to the PERST# pin at the M.2 slot;
> - GPIO 220 is connected to the PERST# pin at the PCIe mini slot;
> - GPIO 203 is connected to the PERST# pin at the Ethernet chipset.
> 
> Maybe due to different electrical requirements, the hardware design
> use different GPIOs instead of feeding them altogether.
> 
> Anyway, the fact is that the PHY on 970 has 4 different GPIOs that are
> need in order for the hardware to work. and this is specific to this
> particular PHY.
> 

I'm not sure about this. That fact that the PCIe device's PERST# signal
wired to different GPIOs doesn't mean that those GPIOs belong to the PHY.
Those GPIOs should be independent of the PCIe core controlled manually
by the driver.

I think this issue is somewhat similar to the one we are dealing on the
Qcom platforms [1] where each PCIe device uses a different GPIO and voltage
config to operate. And those need to be active for the link training to
succeed.

So perhaps we should aim for a common solution? The GPIO and voltage
layout should be described in DT for each port exposed by the SoC/board.

Thanks,
Mani

[1] https://lkml.org/lkml/2021/6/21/1524