Re: [PATCH v3] PCI: mediatek-gen3: Avoid PCIe resetting via PCIE_RSTB for Airoha EN7581 SoC

[Lorenzo Bianconi <lorenzo@kernel.org>]

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> On Wed, Nov 13, 2024 at 02:58:08PM +0100, Lorenzo Bianconi wrote:
> > Airoha EN7581 has a hw bug asserting/releasing PCIE_PE_RSTB signal
> > causing occasional PCIe link down issues. In order to overcome the
> > problem, PCIE_RSTB signals are not asserted/released during device probe or
> > suspend/resume phase and the PCIe block is reset using REG_PCI_CONTROL
> > (0x88) and REG_RESET_CONTROL (0x834) registers available in the clock
> > module running clk_bulk_prepare_enable in mtk_pcie_en7581_power_up().
> > 
> > Introduce flags field in the mtk_gen3_pcie_pdata struct in order to
> > specify per-SoC capabilities.

Hi Bjorn,

similar to the other series, this patch is already in Krzysztof's branch.
Do you prefer to resend it or just incremental changes?

> 
> Is there a URL or some other way to cite erratum documentation for
> this?
> 
> > Tested-by: Hui Ma <hui.ma@airoha.com>
> > Signed-off-by: Lorenzo Bianconi <lorenzo@kernel.org>
> > ---
> > Changes in v3:
> > - cosmetics
> > - Link to v2: https://lore.kernel.org/r/20241104-pcie-en7581-rst-fix-v2-1-ffe5839c76d8@kernel.org
> > 
> > Changes in v2:
> > - introduce flags field in mtk_gen3_pcie_flags struct instead of adding
> >   reset callback
> > - fix the leftover case in mtk_pcie_suspend_noirq routine
> > - add more comments
> > - Link to v1: https://lore.kernel.org/r/20240920-pcie-en7581-rst-fix-v1-1-1043fb63ffc9@kernel.org
> > ---
> >  drivers/pci/controller/pcie-mediatek-gen3.c | 60 ++++++++++++++++++++---------
> >  1 file changed, 42 insertions(+), 18 deletions(-)
> > 
> > diff --git a/drivers/pci/controller/pcie-mediatek-gen3.c b/drivers/pci/controller/pcie-mediatek-gen3.c
> > index 16a55711a7f3bdc8d6620029e3d2cfdd40b537b7..443072adb9b52a6934a5d1e38eb6fca5f86a1e13 100644
> > --- a/drivers/pci/controller/pcie-mediatek-gen3.c
> > +++ b/drivers/pci/controller/pcie-mediatek-gen3.c
> > @@ -128,10 +128,18 @@
> >  
> >  struct mtk_gen3_pcie;
> >  
> > +enum mtk_gen3_pcie_flags {
> > +	SKIP_PCIE_RSTB	= BIT(0), /* skip PCIE_RSTB signals configuration
> > +				   * during device probing or suspend/resume
> > +				   * phase in order to avoid hw bugs/issues.
> 
> Maybe "Skip PERST# assertion"?
> 
> s/in order to/to/

ack, I will fix it.

> 
> > +				   */
> > +};
> > +
> >  /**
> >   * struct mtk_gen3_pcie_pdata - differentiate between host generations
> >   * @power_up: pcie power_up callback
> >   * @phy_resets: phy reset lines SoC data.
> > + * @flags: pcie device flags.
> >   */
> >  struct mtk_gen3_pcie_pdata {
> >  	int (*power_up)(struct mtk_gen3_pcie *pcie);
> > @@ -139,6 +147,7 @@ struct mtk_gen3_pcie_pdata {
> >  		const char *id[MAX_NUM_PHY_RESETS];
> >  		int num_resets;
> >  	} phy_resets;
> > +	u32 flags;
> >  };
> >  
> >  /**
> > @@ -405,22 +414,34 @@ static int mtk_pcie_startup_port(struct mtk_gen3_pcie *pcie)
> >  	val |= PCIE_DISABLE_DVFSRC_VLT_REQ;
> >  	writel_relaxed(val, pcie->base + PCIE_MISC_CTRL_REG);
> >  
> > -	/* Assert all reset signals */
> > -	val = readl_relaxed(pcie->base + PCIE_RST_CTRL_REG);
> > -	val |= PCIE_MAC_RSTB | PCIE_PHY_RSTB | PCIE_BRG_RSTB | PCIE_PE_RSTB;
> > -	writel_relaxed(val, pcie->base + PCIE_RST_CTRL_REG);
> > -
> >  	/*
> > -	 * Described in PCIe CEM specification sections 2.2 (PERST# Signal)
> > -	 * and 2.2.1 (Initial Power-Up (G3 to S0)).
> > -	 * The deassertion of PERST# should be delayed 100ms (TPVPERL)
> > -	 * for the power and clock to become stable.
> > +	 * Airoha EN7581 has a hw bug asserting/releasing PCIE_PE_RSTB signal
> > +	 * causing occasional PCIe link down. In order to overcome the issue,
> > +	 * PCIE_RSTB signals are not asserted/released at this stage and the
> > +	 * PCIe block is reset configuting REG_PCI_CONTROL (0x88) and
> 
> s/configuting/configuring/
> 
> "... is reset configuring ..." doesn't read smoothly.  Maybe "reset
> *using*" or similar?  (I guess "reset using" is what you wrote in the
> commit log.)
> 
> I think if you mention the name of the en7581 clk function, that would
> be enough, and we wouldn't need the register names, offsets, and
> "available in the clock module".

ack, I will fix it.

> 
> > +	 * REG_RESET_CONTROL (0x834) registers available in the clock module
> > +	 * running clk_bulk_prepare_enable in mtk_pcie_en7581_power_up().
> 
> Mention the en7581 clk function, not the generic
> clk_bulk_prepare_enable().  It's hard to get from generic to specific.

ack, I will fix it.

> 
> > -	msleep(100);
> > -
> > -	/* De-assert reset signals */
> > -	val &= ~(PCIE_MAC_RSTB | PCIE_PHY_RSTB | PCIE_BRG_RSTB | PCIE_PE_RSTB);
> > -	writel_relaxed(val, pcie->base + PCIE_RST_CTRL_REG);
> > +	if (!(pcie->soc->flags & SKIP_PCIE_RSTB)) {
> > +		/* Assert all reset signals */
> > +		val = readl_relaxed(pcie->base + PCIE_RST_CTRL_REG);
> > +		val |= PCIE_MAC_RSTB | PCIE_PHY_RSTB | PCIE_BRG_RSTB |
> > +		       PCIE_PE_RSTB;
> > +		writel_relaxed(val, pcie->base + PCIE_RST_CTRL_REG);
> > +
> > +		/*
> > +		 * Described in PCIe CEM specification sections 2.2 (PERST# Signal)
> > +		 * and 2.2.1 (Initial Power-Up (G3 to S0)).
> > +		 * The deassertion of PERST# should be delayed 100ms (TPVPERL)
> > +		 * for the power and clock to become stable.
> 
> Add PCIe CEM spec revision, since section numbers may change between
> revisions.  I know you're just moving it, but this is a good chance to
> fix this.

ack, I will fix it.
> 
> Add blank lines between paragraphs.

ack, I will fix it.
> 
> > +		msleep(PCIE_T_PVPERL_MS);
> > +
> > +		/* De-assert reset signals */
> > +		val &= ~(PCIE_MAC_RSTB | PCIE_PHY_RSTB | PCIE_BRG_RSTB |
> > +			 PCIE_PE_RSTB);
> > +		writel_relaxed(val, pcie->base + PCIE_RST_CTRL_REG);
> > +	}
> >  
> >  	/* Check if the link is up or not */
> >  	err = readl_poll_timeout(pcie->base + PCIE_LINK_STATUS_REG, val,
> > @@ -1179,10 +1200,12 @@ static int mtk_pcie_suspend_noirq(struct device *dev)
> >  		return err;
> >  	}
> >  
> > -	/* Pull down the PERST# pin */
> > -	val = readl_relaxed(pcie->base + PCIE_RST_CTRL_REG);
> > -	val |= PCIE_PE_RSTB;
> > -	writel_relaxed(val, pcie->base + PCIE_RST_CTRL_REG);
> > +	if (!(pcie->soc->flags & SKIP_PCIE_RSTB)) {
> > +		/* Pull down the PERST# pin */
> 
> s/Pull down .../Assert PERST#/ to match other comments above

ack, I will fix it.

Regards,
Lorenzo

> 
> > +		val = readl_relaxed(pcie->base + PCIE_RST_CTRL_REG);
> > +		val |= PCIE_PE_RSTB;
> > +		writel_relaxed(val, pcie->base + PCIE_RST_CTRL_REG);
> > +	}
> >  
> >  	dev_dbg(pcie->dev, "entered L2 states successfully");
> >  
> > @@ -1233,6 +1256,7 @@ static const struct mtk_gen3_pcie_pdata mtk_pcie_soc_en7581 = {
> >  		.id[2] = "phy-lane2",
> >  		.num_resets = 3,
> >  	},
> > +	.flags = SKIP_PCIE_RSTB,
> >  };
> >  
> >  static const struct of_device_id mtk_pcie_of_match[] = {
> > 
> > ---
> > base-commit: ff80d707f3cb5e8d9ec0739e0e5ed42dea179125
> > change-id: 20240920-pcie-en7581-rst-fix-8161658c13c4
> > 
> > Best regards,
> > -- 
> > Lorenzo Bianconi <lorenzo@kernel.org>
> > 

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