linux-kernel - Re: [PATCH v2] PCI: dw-rockchip: Enable async probe by default

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Message-ID: <CANAwSgQ_gojVxvi_OyHTyTSdzRrno=Yymn0AdEXyTHTgDTyFcA@mail.gmail.com>
Date: Mon, 6 Jan 2025 13:28:27 +0530
From: Anand Moon <linux.amoon@...il.com>
To: Andrew Lunn <andrew@...n.ch>
Cc: Niklas Cassel <cassel@...nel.org>, 
	Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>, 
	Lorenzo Pieralisi <lpieralisi@...nel.org>, Krzysztof Wilczyński <kw@...ux.com>, 
	Rob Herring <robh@...nel.org>, Bjorn Helgaas <bhelgaas@...gle.com>, Heiko Stuebner <heiko@...ech.de>, 
	linux-pci@...r.kernel.org, linux-arm-kernel@...ts.infradead.org, 
	linux-rockchip@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] PCI: dw-rockchip: Enable async probe by default

Hi Andrew,

On Sun, 5 Jan 2025 at 23:27, Andrew Lunn <andrew@...n.ch> wrote:
>
> On Sun, Jan 05, 2025 at 11:16:21PM +0530, Anand Moon wrote:
> > Hi Andrew,
> >
> > On Fri, 3 Jan 2025 at 21:34, Andrew Lunn <andrew@...n.ch> wrote:
> > >
> > > > +&gmac1 {
> > > > +       clock_in_out = "output";
> > > > +       phy-handle = <&rgmii_phy1>;
> > > > +       phy-mode = "rgmii";
> > >
> > > rgmii is wrong. Please search the archives about this topic, it comes
> > > up every month. You need to remove the tx_delay and rx_delay
> > > properties, and use rgmii-id.
> > >
> > According to the RKRK3588 TRM-Part1 (section 25.6.11 Clock
> > Architecture), in RGMII mode,
> > the TX clock source is exclusively derived from the CRU (Clock Request Unit).
> > To dynamically adjust the timing alignment between TX/RX clocks and
> > data, delay lines are
> > integrated into both the TX and RX clock paths.
> >
> > Register SYS_GRF_SOC_CON7[5:2] enables these delay lines,
> > while registers SYS_GRF_SOC_CON8[15:0] and SYS_GRF_SOC_CON9[15:0]
> > are used to configure the delay length for each path respectively.
> > Each delay line comprises 200 individual delay elements.
> >
> > Therefore, it is necessary to configure both TX and RX delay values
> > appropriately
> > with phy-mode set as rgmii.
> >
> > [1[ https://github.com/torvalds/linux/blob/master/drivers/net/ethernet/stmicro/stmmac/dwmac-rk.c#L1889-L1914
> >
> > I have gone through a few of the archives about this topic
> >
> > [2] https://lore.kernel.org/linux-rockchip/4fdcb631-16cd-d5f1-e2be-19ecedb436eb@linaro.org/T/
>
> O.K, let me repeat what i have said a number of times over the last
> couple of years.
>
> phy-mode = "rgmii" means the PCB has extra long clock lines on the
> PCB, so the 2ns delay is provided by them.
>
> phy-mode = "rgmii-id" means the MAC/PHY pair need to arrange to add
> the 2ns delay. As far as the DT binding is concerned, it does not
> matter which of the two does the delay. However, there is a convention
> that the PHY adds the delay, if possible.
>
> So, does your PCB have extra long clock lines?
>
> Vendors often just hack until it works. But works does not mean
> correct. I try to review as many .dts files as i can, but some do get
> passed me, so there are plenty of bad examples in mainline.
>
>         Andrew

Thanks for this tip, I am no expert in hardware design.

Here is the schematic design of the board, it looks like RTL8125B page 24
is controlled by a PCIe 2.0 bus

[0] https://dl.radxa.com/rock5/5b/docs/hw/radxa_rock5b_v13_sch.pdf

PERSTB              ---<< PCIE_PERST_L (GPIO3_B0_u)
LANWAKER        --->> PCIE20_1_2_WAKEn_M1_L (GPIO3_D0_u)
LAN_CLKREQB  --->> PCIE20_1_2_CLKREQn_M1_L( GPIO3_C7_u)
IOLATEB             --->> +V3P3A

PCIE2.0 DATA Impedance 85 R

PCIE_WLAN_TX_C_DP  ----->PCIE20_0_TXP
PCIE_WLAN_TX_C_DN  ----->PCIE20_0_TXN

PCIE2.0 CLK Impedance 100 R

PCIE3_WLAN_REFCLK0_DP --> PCIE20_0_REFCLKP
PCIE3_WLAN_REFCLK0_DN--->PCIE20_0_REFCLKN

I have no idea about the grf clk and data path delay over here.

Thanks
-Anand