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From:   Rob Herring <robh@kernel.org>
Date:   Wed, 14 Jul 2021 08:17:05 -0600
Message-ID: <CAL_JsqJehoGakG1kXs8XC_c4UHfVE9oF2M3Ww9eizCa_Jn_TDQ@mail.gmail.com>
Subject: Re: [PATCH v5 2/8] dt-bindings: phy: Add bindings for HiKey 970 PCIe PHY
To:     Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Cc:     Bjorn Helgaas <helgaas@kernel.org>, Linuxarm <linuxarm@huawei.com>,
        mauro.chehab@huawei.com, Manivannan Sadhasivam <mani@kernel.org>,
        Kishon Vijay Abraham I <kishon@ti.com>,
        Vinod Koul <vkoul@kernel.org>, devicetree@vger.kernel.org,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        linux-phy@lists.infradead.org
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On Wed, Jul 14, 2021 at 1:14 AM Mauro Carvalho Chehab
<mchehab+huawei@kernel.org> 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.

This hierarchy could be done on any board. It has nothing to do with the PHY.

> Now, from software perspective, the power on sequence on Hikey 960
> finishes sending PERST# signal to the M.2 slot:
>
>         static int hi3660_pcie_phy_power_on(struct phy *generic_phy)
>         {
> ...
>                 /* perst assert Endpoint */
>                 if (!gpio_request(phy->gpio_id_reset, "pcie_perst")) {
>                         usleep_range(REF_2_PERST_MIN, REF_2_PERST_MAX);
>                         ret = gpio_direction_output(phy->gpio_id_reset, 1);
>                         if (ret)
>                                 goto disable_clks;
>                         usleep_range(PERST_2_ACCESS_MIN, PERST_2_ACCESS_MAX);
>                         return 0;
>                 }
>
>         disable_clks:
>                 kirin_pcie_clk_ctrl(phy, false);
>                 return ret;
>         }
>
> The 970 PHY, however, sends PERST# signal in the middle of the power
> on sequence, as, after sending reset, it needs to wait for the hardware
> to stabilize, in order to setup an eye diagram at the PHY:
>
>         static int hi3670_pcie_phy_power_on(struct phy *generic_phy)
>         {
> ...
>                 /* perst assert Endpoints */
>                 usleep_range(21000, 23000);
>                 for (i = 0; i < phy->n_gpio_resets; i++) {
>                         ret = gpio_direction_output(phy->gpio_id_reset[i], 1);
>                         if (ret)
>                                 return ret;
>                 }
>                 usleep_range(10000, 11000);
>
>                 ret = is_pipe_clk_stable(phy);
>                 if (!ret)
>                         goto disable_clks;
>
>                 hi3670_pcie_set_eyeparam(phy);
>
>                 ret = hi3670_pcie_noc_power(phy, false);
>                 if (ret)
>                         goto disable_clks;
>
>                 return 0;
>
>         disable_clks:
>                 kirin_pcie_clk_ctrl(phy, false);
>                 return ret;
>         }
>
> IMO, it makes a lot more sense to map this on DT as part of the
> PHY and not as part of the PCIe, but no matter how it is mapped,
> this PHY still requires 4 GPIOs for PERST#.

It does not because PERST# control is part of PCIe for every other driver.

Rob