[PATCH v2] PCI: imx6: Fix PERST# start-up sequence

[PATCH v2] PCI: imx6: Fix PERST# start-up sequence

[Francesco Dolcini]

According to the PCIe standard the PERST# signal (reset-gpio in
fsl,imx* compatible dts) should be kept asserted for at least 100 usec
before the PCIe refclock is stable, should be kept asserted for at
least 100 msec after the power rails are stable and the host should wait
at least 100 msec after it is de-asserted before accessing the
configuration space of any attached device.

From PCIe CEM r2.0, sec 2.6.2

  T-PVPERL: Power stable to PERST# inactive - 100 msec
  T-PERST-CLK: REFCLK stable before PERST# inactive - 100 usec.

From PCIe r5.0, sec 6.6.1

  With a Downstream Port that does not support Link speeds greater than
  5.0 GT/s, software must wait a minimum of 100 ms before sending a
  Configuration Request to the device immediately below that Port.

Failure to do so could prevent PCIe devices to be working correctly,
and this was experienced with real devices.

Move reset assert to imx6_pcie_assert_core_reset(), this way we ensure
that PERST# is asserted before enabling any clock, move de-assert to the
end of imx6_pcie_deassert_core_reset() after the clock is enabled and
deemed stable and add a new delay of 100 msec just afterward.

Link: https://lore.kernel.org/all/20220211152550.286821-1-francesco.dolcini@toradex.com
Fixes: bb38919ec56e ("PCI: imx6: Add support for i.MX6 PCIe controller")
Signed-off-by: Francesco Dolcini <francesco.dolcini@toradex.com>
---
v2: Add complete reference to the PCIe standards, s/PCI-E/PCIe/g
---
 drivers/pci/controller/dwc/pci-imx6.c | 23 ++++++++++++++---------
 1 file changed, 14 insertions(+), 9 deletions(-)

diff --git a/drivers/pci/controller/dwc/pci-imx6.c b/drivers/pci/controller/dwc/pci-imx6.c
index 7b200b66114a..73baa2044ccf 100644
--- a/drivers/pci/controller/dwc/pci-imx6.c
+++ b/drivers/pci/controller/dwc/pci-imx6.c
@@ -408,6 +408,11 @@ static void imx6_pcie_assert_core_reset(struct imx6_pcie *imx6_pcie)
 			dev_err(dev, "failed to disable vpcie regulator: %d\n",
 				ret);
 	}
+
+	/* Some boards don't have PCIe reset GPIO. */
+	if (gpio_is_valid(imx6_pcie->reset_gpio))
+		gpio_set_value_cansleep(imx6_pcie->reset_gpio,
+					imx6_pcie->gpio_active_high);
 }
 
 static unsigned int imx6_pcie_grp_offset(const struct imx6_pcie *imx6_pcie)
@@ -544,15 +549,6 @@ static void imx6_pcie_deassert_core_reset(struct imx6_pcie *imx6_pcie)
 	/* allow the clocks to stabilize */
 	usleep_range(200, 500);
 
-	/* Some boards don't have PCIe reset GPIO. */
-	if (gpio_is_valid(imx6_pcie->reset_gpio)) {
-		gpio_set_value_cansleep(imx6_pcie->reset_gpio,
-					imx6_pcie->gpio_active_high);
-		msleep(100);
-		gpio_set_value_cansleep(imx6_pcie->reset_gpio,
-					!imx6_pcie->gpio_active_high);
-	}
-
 	switch (imx6_pcie->drvdata->variant) {
 	case IMX8MQ:
 		reset_control_deassert(imx6_pcie->pciephy_reset);
@@ -599,6 +595,15 @@ static void imx6_pcie_deassert_core_reset(struct imx6_pcie *imx6_pcie)
 		break;
 	}
 
+	/* Some boards don't have PCIe reset GPIO. */
+	if (gpio_is_valid(imx6_pcie->reset_gpio)) {
+		msleep(100);
+		gpio_set_value_cansleep(imx6_pcie->reset_gpio,
+					!imx6_pcie->gpio_active_high);
+		/* Wait for 100ms after PERST# deassertion (PCIe r5.0, 6.6.1) */
+		msleep(100);
+	}
+
 	return;
 
 err_ref_clk:
-- 
2.25.1

RE: [PATCH v2] PCI: imx6: Fix PERST# start-up sequence

[Hongxing Zhu]

[-- Warning: decoded text below may be mangled, UTF-8 assumed --]
[-- Attachment #1: Type: text/plain; charset="gb2312", Size: 4708 bytes --]

> -----Original Message-----
> From: Francesco Dolcini <francesco.dolcini@toradex.com>
> Sent: 2022Äê2ÔÂ15ÈÕ 0:15
> To: Hongxing Zhu <hongxing.zhu@nxp.com>; Lucas Stach
> <l.stach@pengutronix.de>; Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>; Rob
> Herring <robh@kernel.org>; Krzysztof Wilczy¨½ski <kw@linux.com>;
> Pengutronix Kernel Team <kernel@pengutronix.de>; Fabio Estevam
> <festevam@gmail.com>; dl-linux-imx <linux-imx@nxp.com>; Bjorn Helgaas
> <helgaas@kernel.org>
> Cc: Francesco Dolcini <francesco.dolcini@toradex.com>; Shawn Guo
> <shawnguo@kernel.org>; Sascha Hauer <s.hauer@pengutronix.de>;
> linux-pci@vger.kernel.org; linux-arm-kernel@lists.infradead.org
> Subject: [PATCH v2] PCI: imx6: Fix PERST# start-up sequence
> 
> According to the PCIe standard the PERST# signal (reset-gpio in
> fsl,imx* compatible dts) should be kept asserted for at least 100 usec before
> the PCIe refclock is stable, should be kept asserted for at least 100 msec after
> the power rails are stable and the host should wait at least 100 msec after it is
> de-asserted before accessing the configuration space of any attached device.
> 
> From PCIe CEM r2.0, sec 2.6.2
> 
>   T-PVPERL: Power stable to PERST# inactive - 100 msec
>   T-PERST-CLK: REFCLK stable before PERST# inactive - 100 usec.
> 
> From PCIe r5.0, sec 6.6.1
> 
>   With a Downstream Port that does not support Link speeds greater than
>   5.0 GT/s, software must wait a minimum of 100 ms before sending a
>   Configuration Request to the device immediately below that Port.
> 
> Failure to do so could prevent PCIe devices to be working correctly, and this
> was experienced with real devices.
> 
> Move reset assert to imx6_pcie_assert_core_reset(), this way we ensure that
> PERST# is asserted before enabling any clock, move de-assert to the end of
> imx6_pcie_deassert_core_reset() after the clock is enabled and deemed stable
> and add a new delay of 100 msec just afterward.
> 
> Link:
> https://eur01.safelinks.protection.outlook.com/?url=https%3A%2F%2Flore.ker
> nel.org%2Fall%2F20220211152550.286821-1-francesco.dolcini%40toradex.co
> m&amp;data=04%7C01%7Chongxing.zhu%40nxp.com%7C28939dcb78a8460f
> c3db08d9efd538cb%7C686ea1d3bc2b4c6fa92cd99c5c301635%7C0%7C0%7C
> 637804521335664249%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAw
> MDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000&amp;sda
> ta=l7vjiJ3KuERmaWYMy09svELcUcI1ekLJPVKpt0AViTo%3D&amp;reserved=0
> Fixes: bb38919ec56e ("PCI: imx6: Add support for i.MX6 PCIe controller")
> Signed-off-by: Francesco Dolcini <francesco.dolcini@toradex.com>
Thanks.
Acked-by: Richard Zhu <hongxing.zhu@nxp.com>

Best Regards
Richard Zhu
> ---
> v2: Add complete reference to the PCIe standards, s/PCI-E/PCIe/g
> ---
>  drivers/pci/controller/dwc/pci-imx6.c | 23 ++++++++++++++---------
>  1 file changed, 14 insertions(+), 9 deletions(-)
> 
> diff --git a/drivers/pci/controller/dwc/pci-imx6.c
> b/drivers/pci/controller/dwc/pci-imx6.c
> index 7b200b66114a..73baa2044ccf 100644
> --- a/drivers/pci/controller/dwc/pci-imx6.c
> +++ b/drivers/pci/controller/dwc/pci-imx6.c
> @@ -408,6 +408,11 @@ static void imx6_pcie_assert_core_reset(struct
> imx6_pcie *imx6_pcie)
>  			dev_err(dev, "failed to disable vpcie regulator: %d\n",
>  				ret);
>  	}
> +
> +	/* Some boards don't have PCIe reset GPIO. */
> +	if (gpio_is_valid(imx6_pcie->reset_gpio))
> +		gpio_set_value_cansleep(imx6_pcie->reset_gpio,
> +					imx6_pcie->gpio_active_high);
>  }
> 
>  static unsigned int imx6_pcie_grp_offset(const struct imx6_pcie *imx6_pcie)
> @@ -544,15 +549,6 @@ static void imx6_pcie_deassert_core_reset(struct
> imx6_pcie *imx6_pcie)
>  	/* allow the clocks to stabilize */
>  	usleep_range(200, 500);
> 
> -	/* Some boards don't have PCIe reset GPIO. */
> -	if (gpio_is_valid(imx6_pcie->reset_gpio)) {
> -		gpio_set_value_cansleep(imx6_pcie->reset_gpio,
> -					imx6_pcie->gpio_active_high);
> -		msleep(100);
> -		gpio_set_value_cansleep(imx6_pcie->reset_gpio,
> -					!imx6_pcie->gpio_active_high);
> -	}
> -
>  	switch (imx6_pcie->drvdata->variant) {
>  	case IMX8MQ:
>  		reset_control_deassert(imx6_pcie->pciephy_reset);
> @@ -599,6 +595,15 @@ static void imx6_pcie_deassert_core_reset(struct
> imx6_pcie *imx6_pcie)
>  		break;
>  	}
> 
> +	/* Some boards don't have PCIe reset GPIO. */
> +	if (gpio_is_valid(imx6_pcie->reset_gpio)) {
> +		msleep(100);
> +		gpio_set_value_cansleep(imx6_pcie->reset_gpio,
> +					!imx6_pcie->gpio_active_high);
> +		/* Wait for 100ms after PERST# deassertion (PCIe r5.0, 6.6.1) */
> +		msleep(100);
> +	}
> +
>  	return;
> 
>  err_ref_clk:
> --
> 2.25.1

Re: [PATCH v2] PCI: imx6: Fix PERST# start-up sequence

[Francesco Dolcini]

Just a gently ping. Should I resend adding the acked-by Richard Zhu?

Francesco

On Mon, Feb 14, 2022 at 05:15:22PM +0100, Francesco Dolcini wrote:
> According to the PCIe standard the PERST# signal (reset-gpio in
> fsl,imx* compatible dts) should be kept asserted for at least 100 usec
> before the PCIe refclock is stable, should be kept asserted for at
> least 100 msec after the power rails are stable and the host should wait
> at least 100 msec after it is de-asserted before accessing the
> configuration space of any attached device.
> 
> From PCIe CEM r2.0, sec 2.6.2
> 
>   T-PVPERL: Power stable to PERST# inactive - 100 msec
>   T-PERST-CLK: REFCLK stable before PERST# inactive - 100 usec.
> 
> From PCIe r5.0, sec 6.6.1
> 
>   With a Downstream Port that does not support Link speeds greater than
>   5.0 GT/s, software must wait a minimum of 100 ms before sending a
>   Configuration Request to the device immediately below that Port.
> 
> Failure to do so could prevent PCIe devices to be working correctly,
> and this was experienced with real devices.
> 
> Move reset assert to imx6_pcie_assert_core_reset(), this way we ensure
> that PERST# is asserted before enabling any clock, move de-assert to the
> end of imx6_pcie_deassert_core_reset() after the clock is enabled and
> deemed stable and add a new delay of 100 msec just afterward.
> 
> Link: https://lore.kernel.org/all/20220211152550.286821-1-francesco.dolcini@toradex.com
> Fixes: bb38919ec56e ("PCI: imx6: Add support for i.MX6 PCIe controller")
> Signed-off-by: Francesco Dolcini <francesco.dolcini@toradex.com>
> ---
> v2: Add complete reference to the PCIe standards, s/PCI-E/PCIe/g
> ---
>  drivers/pci/controller/dwc/pci-imx6.c | 23 ++++++++++++++---------
>  1 file changed, 14 insertions(+), 9 deletions(-)
> 
> diff --git a/drivers/pci/controller/dwc/pci-imx6.c b/drivers/pci/controller/dwc/pci-imx6.c
> index 7b200b66114a..73baa2044ccf 100644
> --- a/drivers/pci/controller/dwc/pci-imx6.c
> +++ b/drivers/pci/controller/dwc/pci-imx6.c
> @@ -408,6 +408,11 @@ static void imx6_pcie_assert_core_reset(struct imx6_pcie *imx6_pcie)
>  			dev_err(dev, "failed to disable vpcie regulator: %d\n",
>  				ret);
>  	}
> +
> +	/* Some boards don't have PCIe reset GPIO. */
> +	if (gpio_is_valid(imx6_pcie->reset_gpio))
> +		gpio_set_value_cansleep(imx6_pcie->reset_gpio,
> +					imx6_pcie->gpio_active_high);
>  }
>  
>  static unsigned int imx6_pcie_grp_offset(const struct imx6_pcie *imx6_pcie)
> @@ -544,15 +549,6 @@ static void imx6_pcie_deassert_core_reset(struct imx6_pcie *imx6_pcie)
>  	/* allow the clocks to stabilize */
>  	usleep_range(200, 500);
>  
> -	/* Some boards don't have PCIe reset GPIO. */
> -	if (gpio_is_valid(imx6_pcie->reset_gpio)) {
> -		gpio_set_value_cansleep(imx6_pcie->reset_gpio,
> -					imx6_pcie->gpio_active_high);
> -		msleep(100);
> -		gpio_set_value_cansleep(imx6_pcie->reset_gpio,
> -					!imx6_pcie->gpio_active_high);
> -	}
> -
>  	switch (imx6_pcie->drvdata->variant) {
>  	case IMX8MQ:
>  		reset_control_deassert(imx6_pcie->pciephy_reset);
> @@ -599,6 +595,15 @@ static void imx6_pcie_deassert_core_reset(struct imx6_pcie *imx6_pcie)
>  		break;
>  	}
>  
> +	/* Some boards don't have PCIe reset GPIO. */
> +	if (gpio_is_valid(imx6_pcie->reset_gpio)) {
> +		msleep(100);
> +		gpio_set_value_cansleep(imx6_pcie->reset_gpio,
> +					!imx6_pcie->gpio_active_high);
> +		/* Wait for 100ms after PERST# deassertion (PCIe r5.0, 6.6.1) */
> +		msleep(100);
> +	}
> +
>  	return;
>  
>  err_ref_clk:
> -- 
> 2.25.1
>