RE: [PATCH v3 0/9] add the imx8m pcie phy driver and imx8mm pcie support

[Richard Zhu <hongxing.zhu@nxp.com>]

> -----Original Message-----
> From: Tim Harvey <tharvey@gateworks.com>
> Sent: Tuesday, October 26, 2021 1:15 AM
> To: Richard Zhu <hongxing.zhu@nxp.com>
> Cc: Lucas Stach <l.stach@pengutronix.de>; Kishon Vijay Abraham I
> <kishon@ti.com>; vkoul@kernel.org; Rob Herring <robh@kernel.org>;
> galak@kernel.crashing.org; Shawn Guo <shawnguo@kernel.org>;
> linux-phy@lists.infradead.org; Device Tree Mailing List
> <devicetree@vger.kernel.org>; Linux ARM Mailing List
> <linux-arm-kernel@lists.infradead.org>; open list
> <linux-kernel@vger.kernel.org>; Sascha Hauer <kernel@pengutronix.de>;
> dl-linux-imx <linux-imx@nxp.com>
> Subject: Re: [PATCH v3 0/9] add the imx8m pcie phy driver and imx8mm pcie
> support
> 
> On Mon, Oct 25, 2021 at 12:23 AM Richard Zhu <hongxing.zhu@nxp.com>
> wrote:
> >
> > Snipped...
> >
> > > > > > > > > My boards do not use CLKREQ# so I do not have that
> > > > > > > > > defined in pinmux and I found that if I add
> > > > > > > > > MX8MM_IOMUXC_I2C4_SCL_PCIE1_CLKREQ_B
> > > > > > > PCIe
> > > > > > > > > works on my board but this isn't a solution just a
> > > > > > > > > work-around (I have boards that use the only two
> > > > > > > > > possible pins for CLKREQ as other
> > > > > > > features).
> > > > > > > > >
> > > > > > > > > Similarly you will find on the imx8mm-evk if you comment
> > > > > > > > > out the CLKREQ (which isn't required) the imx8mmevk will
> > > > > > > > > end up hanging like my
> > > > > > > boards:
> > > > > > > > [Richard Zhu] Hi Tim:
> > > > > > > > Regarding the SPEC, the CLKREQ# is mandatory required, and
> > > > > > > > should be
> > > > > > > configured as an open drain, active low signal.
> > > > > > > > And this signal should be driven low by the PCIe M.2
> > > > > > > > device to request the
> > > > > > > REF clock be available(active low).
> > > > > > > > So, there is such kind of CLKREQ# pin definition on
> > > > > > > > i.MX8MM EVK
> > > > board.
> > > > > > > >
> > > > > > > > Anyway, I think the external OSC circuit should be always
> > > > > > > > running if there is
> > > > > > > no CLKREQ# on your HW board design.
> > > > > > > >
> > > > > > >
> > > > > > > The way I understand it is CLKREQ# allows the host to
> > > > > > > disable the REFCLK when not needed for power savings so it
> > > > > > > would seem optional to implement that and if not implemented
> > > > > > > should be left unconnected on
> > > > the card.
> > > > > > >
> > > > > > [Richard Zhu] No, not that way. Regarding the SPEC, this
> > > > > > signal is
> > > > mandatory required.
> > > > > > Especially for the L1ss usages. This signal would be OD(open
> > > > > > drain), bi-directional, and might be driven low/high by RC or
> > > > > > EP automatically if
> > > > L1ss modes are enabled.
> > > > > > You can make reference to the
> > > > > > "ECN_L1_PM_Substates_with_CLKREQ_31_May_2013_Rev10a", or
> the
> > > > chapter 5.5 L1 PM Substates of "PCI Express Base Specification, Rev.
> > > > 4.0 Version 1.0".
> > > > > >
> > > > >
> > > > > CLKREQ is only mandatory if you wish to support clock power
> > > > > management. Many boards with a PCI host controller do not
> > > > > support this.
> > > [Richard Zhu] Okay, understood.
> > >
> > > > >
> > > > > > > > > diff --git
> > > > > > > > > a/arch/arm64/boot/dts/freescale/imx8mm-evk.dtsi
> > > > > > > > > b/arch/arm64/boot/dts/freescale/imx8mm-evk.dtsi
> > > > > > > > > index 5ce43daa0c8b..f0023b48f475 100644
> > > > > > > > > --- a/arch/arm64/boot/dts/freescale/imx8mm-evk.dtsi
> > > > > > > > > +++ b/arch/arm64/boot/dts/freescale/imx8mm-evk.dtsi
> > > > > > > > > @@ -448,7 +448,9 @@
> > > > > > > > >
> > > > > > > > >         pinctrl_pcie0: pcie0grp {
> > > > > > > > >                 fsl,pins = <
> > > > > > > > > +/*
> > > > > > > > >
> > > > > > > > > MX8MM_IOMUXC_I2C4_SCL_PCIE1_CLKREQ_B    0x61
> > > > > > > > > +*/
> > > > > > > > >
> > > > > > > MX8MM_IOMUXC_SAI2_RXFS_GPIO4_IO21
> > > > > > > > > 0x41
> > > > > > > > >                 >;
> > > > > > > > >         };
> > > > > > > > >
> > > > > > > > > I have PCIe working with a driver that I ported from
> > > > > > > > > NXP's kernel which differs from your driver in that the
> > > > > > > > > PCIe PHY is not abstracted to its own driver so I think
> > > > > > > > > this has something to do with the order in which the phy
> > > > > > > > > is reset or
> > > initialized?
> > > > > > > > > The configuration of
> > > > > > > gpr14 bits looks correct to me.
> > > > > > > > [Richard Zhu] The CLKREQ# PIN definition shouldn't be masked.
> > > > > > > > In the NXP's local BSP kernel, I just force CLKREQ# low to
> > > > > > > > level up the HW
> > > > > > > compatibility.
> > > > > > > > That's might the reason why the PCIe works on your HW
> > > > > > > > board although the
> > > > > > > CLKREQ# PIN is not defined.
> > > > > > > > This method is a little rude and violate the SPEC, and not
> > > > > > > > recommended
> > > > > > > although it levels up the HW compatibility.
> > > > > > > > So I drop this method in this series.
> > > > > > > >
> > > > > > >
> > > > > > > Sorry, I don't understand what you are saying here. Is there
> > > > > > > a change you are going to make to v4 that will make this
> > > > > > > work for the evk and my boards? What is that change exactly?
> > > > > > [Richard Zhu] No. What I said above is that the CLKREQ# is
> > > > > > forced to be low in NXP local BSP kernel. I guess this might
> > > > > > be the reason why your
> > > > board works.
> > > > > >
> > > > > > BIT11 and BIT10 of IOMUXC_GPR14 can be used to force the
> > > > > > CLKREQ# to
> > > > be low.
> > > > > > Set CLKREQ_OVERRIDE_EN(bit10) 1b1, then write one zero to
> > > > CLKREQ_OVERRIDE(bit11).
> > > > > >
> > > > >
> > > > > Ok, that makes sense. Those bits are not explained well in the
> > > > > IMX8MMRM. As my board's external REFCLK is always enabled that
> > > > > must gate the clock internally to the host controller block.
> > > > >
> > > > > I can confirm that asserting those GPR14 bits does resolve my issue:
> > > > >
> > > > > #define IMX8MM_GPR_PCIE_CLKREQ_OVERRIDE_VAL    BIT(11)
> > > > > #define IMX8MM_GPR_PCIE_CLKREQ_OVERRIDE_EN     BIT(10)
> > > > >
> > > > >        /*
> > > > >         * for boards that do not connect CLKREQ#,
> > > > >         * override CLKREQ# and drive it low internally
> > > > >         */
> > > > >        regmap_update_bits(imx8_phy->iomuxc_gpr,
> IOMUXC_GPR14,
> > > > >
> > > > IMX8MM_GPR_PCIE_CLKREQ_OVERRIDE_VAL, 0);
> > > > >        regmap_update_bits(imx8_phy->iomuxc_gpr,
> IOMUXC_GPR14,
> > > > >
> > > > IMX8MM_GPR_PCIE_CLKREQ_OVERRIDE_EN, 1);
> > > [Richard Zhu] regmap bits operations should manipulate according bits.
> > > The BIT(10) and BIT(11) should be touched actually.
> > >
> > > > >
> > > > > Should this be added as a 'fsl,clkreq-unsupported' flag that
> > > > > needs to be set true to implement the above code?
> > > > >
> > > >
> > > > Richard,
> > > >
> > > > Sorry - spoke too soon. My test was flawed as I still was
> > > > pinmuxing CLKREQ in my dt to work around the issue and after
> > > > removed the above did not resolve my issue. The setting of
> > > > OVERRIDE_EN was wrong above (should not be set to '1' but BIT(10)
> > > > instead) but this code already exists in imx6_pcie_enable_ref_clk
> > > > and is used for IMX8MM per your patch so this is not the issue.
> > > >
> > > > What makes my board work is to clear GPR14 bit9 (like the NXP
> > > > kernel
> > > > does) so I don't think this bit does what we think it does (select
> > > > between internal and ext clk). I think setting it enables clock
> > > > gating via
> > > CLKREQ#.
> > > >
> > > > This also points out that perhaps the CLKREQ_OVERRIDE logic should
> > > > be moved to the new phy driver for IMX8MM.
> > > [Richard Zhu] It sounds reasonable to consider to force the CLKREQ#
> > > to be low.
> > > I will think about that and add this in later v5 patch-set if nobody
> > > has different concerns.
> > > Thanks.
> > [Richard Zhu] Hi Tim:
> > As you mentioned above, the CLKREQ# GPIO PIN is not used for PCIe on
> your board, right?
> > " (I have boards that use the only two possible pins for CLKREQ as other
> features)"
> >
> > Did the override configuration of the clkreq# will bring unexpected results
> for other features on your board?
> >
> 
> What I mean is that imx8mm-venice-gw7901.dts uses both I2C4 and UART4
> and because I2C4_SCL and UART4_RXD are the only two pads that could be
> pinmuxed for CLKREQ# I can't use the workaround of pin muxing it.
> 
> Currently your driver only works on my imx8mm-venice-* boards if I add one
> of the following on boards that don't connect those pads (or if I clear
> IMX8MM_GPR_PCIE_REF_USE_PAD):
> MX8MM_IOMUXC_I2C4_SCL_PCIE1_CLKREQ_B
> MX8MM_IOMUXC_UART4_RXD_PCIE1_CLKREQ_B
> 
> Note your 'PCI: imx: add the imx8mm pcie support' patch [1] does enable this
> code already in the imx6_pcie_enable_ref_clk function to override REF_CLK
> and drive it low:
> 
> offset = imx6_pcie_grp_offset(imx6_pcie);
> /*
> * Set the over ride low and enabled
> * make sure that REF_CLK is turned on.
> */
> regmap_update_bits(imx6_pcie->iomuxc_gpr, offset,
>    IMX8MQ_GPR_PCIE_CLK_REQ_OVERRIDE,
>    0);
> regmap_update_bits(imx6_pcie->iomuxc_gpr, offset,
>    IMX8MQ_GPR_PCIE_CLK_REQ_OVERRIDE_EN,
>    IMX8MQ_GPR_PCIE_CLK_REQ_OVERRIDE_EN);
> 
> So this is already being run and yet my boards still do not work unless I clr
> IMX8MM_GPR_PCIE_REF_USE_PAD like this which is what the NXP
> downstream driver does:
> regmap_update_bits(imx8_phy->iomuxc_gpr, IOMUXC_GPR14,
> IMX8MM_GPR_PCIE_REF_USE_PAD, 0);
> 
> This is why I'm not sure that bit does what you think it does... I feel like that
> bit enables 'Use CLKREQ# to enable CLK'.
> 
> You tell me the descriptions for GPR14 are wrong in the reference manual.
> Please provide correct descriptions for us so we can sort this out.
> 
[Richard Zhu] Hi Tim:
The BIT9 of GPR14 is used as "GPR_PCIE1_PHY_I_AUX_EN_OVERRIDE_EN"
and BIT19 is used as "GPR_PCIE1_PHY_FUNC_I_AUX_EN" on i.MX8MM.
I think the two bits descriptions are used to describe the BIT19 and BIT9 together refer to my guess.
{GPR_PCIE1_PHY_I_AUX_EN_OVERRIDE_EN(BIT9), GPR_PCIE1_PHY_FUNC_I_AUX_EN(BIT19) }
2'b00: External Reference Clock I/O (for PLL) Disable
2'b01: External Reference Clock I/O (for PLL) Enable
2'b10: External Reference Clock I/O (for PLL) Disable
2'b11: External Reference Clock I/O (for PLL) output is controlled by CLKREQ#

The option1&3 should be forbidden, since the external REF CLK I/O should be enabled on your board and EVK board.
In the option2&4, the BIT19 should be set to be 1'b1.

So, regarding my understand, if the CLKREQ# is not pinmuxed in your use case, the IMX8MM_GPR_PCIE_REF_USE_PAD (BIT9) should be 1'b0.

BR
Richard
> Best regards,
> 
> Tim
> [1]
> https://eur01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fpatch
> work.kernel.org%2Fproject%2Flinux-arm-kernel%2Fpatch%2F1634028078-23
> 87-10-git-send-email-hongxing.zhu%40nxp.com%2F&amp;data=04%7C01%7
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> 7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJ
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> I7GE62hy64Bumxr8WdCD1oh59w%3D&amp;reserved=0