* [PATCH v1] PCI: imx6: Fix PERST# start-up sequence
@ 2022-02-11 15:25 Francesco Dolcini
2022-02-11 18:18 ` Bjorn Helgaas
0 siblings, 1 reply; 3+ messages in thread
From: Francesco Dolcini @ 2022-02-11 15:25 UTC (permalink / raw)
To: Richard Zhu, Lucas Stach, Lorenzo Pieralisi, Rob Herring,
Krzysztof Wilczyński, Pengutronix Kernel Team,
Fabio Estevam, NXP Linux Team
Cc: Francesco Dolcini, Shawn Guo, Sascha Hauer, linux-pci, linux-arm-kernel
According to the PCI-E standard the PERST# signal (reset-gpio in
fsl,imx6* compatible dts) should be kept asserted for at least 100 usec
before the PCI-E refclock is stable, should be kept asserted for at
least 100ms 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 PCI Express Card Electromechanical Specification
T-PVPERL: Power stable to PERST# inactive - 100 msec
T-PERST-CLK: REFCLK stable before PERST# inactive 100 usec.
From PCI Express Base Specification:
To allow components to perform internal initialization, system
software must wait for at least 100 ms from the end of a Conventional
Reset of one or more devices before it is permitted to issue
Configuration Requests to those devices
Failure to do so could prevent PCI-E 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.
Fixes: bb38919ec56e ("PCI: imx6: Add support for i.MX6 PCIe controller")
Signed-off-by: Francesco Dolcini <francesco.dolcini@toradex.com>
---
drivers/pci/controller/dwc/pci-imx6.c | 27 ++++++++++++++++++---------
1 file changed, 18 insertions(+), 9 deletions(-)
diff --git a/drivers/pci/controller/dwc/pci-imx6.c b/drivers/pci/controller/dwc/pci-imx6.c
index 7b200b66114a..392803544364 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 +595,19 @@ 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);
+ /*
+ * PCI Express Base Specification:
+ * A delay of at least 100ms is required after PERST# is
+ * de-asserted before issuing any Configuration Requests
+ */
+ msleep(100);
+ }
+
return;
err_ref_clk:
--
2.25.1
^ permalink raw reply related [flat|nested] 3+ messages in thread
* Re: [PATCH v1] PCI: imx6: Fix PERST# start-up sequence
2022-02-11 15:25 [PATCH v1] PCI: imx6: Fix PERST# start-up sequence Francesco Dolcini
@ 2022-02-11 18:18 ` Bjorn Helgaas
2022-02-14 13:20 ` Francesco Dolcini
0 siblings, 1 reply; 3+ messages in thread
From: Bjorn Helgaas @ 2022-02-11 18:18 UTC (permalink / raw)
To: Francesco Dolcini
Cc: Richard Zhu, Lucas Stach, Lorenzo Pieralisi, Rob Herring,
Krzysztof Wilczyński, Pengutronix Kernel Team,
Fabio Estevam, NXP Linux Team, Shawn Guo, Sascha Hauer,
linux-pci, linux-arm-kernel
On Fri, Feb 11, 2022 at 04:25:50PM +0100, Francesco Dolcini wrote:
> According to the PCI-E standard the PERST# signal (reset-gpio in
s/PCI-E/PCIe/ everywhere, to match conventional usage.
> fsl,imx6* compatible dts) should be kept asserted for at least 100 usec
> before the PCI-E refclock is stable, should be kept asserted for at
> least 100ms 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 PCI Express Card Electromechanical Specification
Please include spec revision and section number. I think this would
probably be "PCIe CEM r5.0, sec 2.9.2".
> T-PVPERL: Power stable to PERST# inactive - 100 msec
> T-PERST-CLK: REFCLK stable before PERST# inactive 100 usec.
>
> From PCI Express Base Specification:
Similarly, "PCIe r6.0, sec xxx". I don't see the text below in r6.0,
so I think it must have evolved a bit. Probably something in sec
6.6.1.
> To allow components to perform internal initialization, system
> software must wait for at least 100 ms from the end of a Conventional
> Reset of one or more devices before it is permitted to issue
> Configuration Requests to those devices
>
> Failure to do so could prevent PCI-E 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.
>
> Fixes: bb38919ec56e ("PCI: imx6: Add support for i.MX6 PCIe controller")
> Signed-off-by: Francesco Dolcini <francesco.dolcini@toradex.com>
> ---
> drivers/pci/controller/dwc/pci-imx6.c | 27 ++++++++++++++++++---------
> 1 file changed, 18 insertions(+), 9 deletions(-)
>
> diff --git a/drivers/pci/controller/dwc/pci-imx6.c b/drivers/pci/controller/dwc/pci-imx6.c
> index 7b200b66114a..392803544364 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 +595,19 @@ 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);
> + /*
> + * PCI Express Base Specification:
Mention spec rev & section here, too. Someday we'll consolidate these
with #defines and identifying all the delays related to sec 6.6.1 (or
whatever it is) will be important.
> + * A delay of at least 100ms is required after PERST# is
> + * de-asserted before issuing any Configuration Requests
> + */
> + msleep(100);
> + }
> +
> return;
>
> err_ref_clk:
> --
> 2.25.1
>
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [PATCH v1] PCI: imx6: Fix PERST# start-up sequence
2022-02-11 18:18 ` Bjorn Helgaas
@ 2022-02-14 13:20 ` Francesco Dolcini
0 siblings, 0 replies; 3+ messages in thread
From: Francesco Dolcini @ 2022-02-14 13:20 UTC (permalink / raw)
To: Bjorn Helgaas
Cc: Francesco Dolcini, Richard Zhu, Lucas Stach, Lorenzo Pieralisi,
Rob Herring, Krzysztof Wilczyński, Pengutronix Kernel Team,
Fabio Estevam, NXP Linux Team, Shawn Guo, Sascha Hauer,
linux-pci, linux-arm-kernel
Hello Bjorn,
thanks for the review.
On Fri, Feb 11, 2022 at 12:18:24PM -0600, Bjorn Helgaas wrote:
> Mention spec rev & section here, too. Someday we'll consolidate these
> with #defines and identifying all the delays related to sec 6.6.1 (or
> whatever it is) will be important.
I added all the references and will send the v2 later today, however I
do not have access to the PCI-SIG specifications anymore, therefore I'll
mention the one I currently have access to (I did not copy the sections
you mentioned just because you wrote "probably" and I had no way to
double check).
I guess that this should not be a big deal, since we already have
different version of the standard mentioned thought the code with
reference to this topic.
Francesco
^ permalink raw reply [flat|nested] 3+ messages in thread
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2022-02-11 15:25 [PATCH v1] PCI: imx6: Fix PERST# start-up sequence Francesco Dolcini
2022-02-11 18:18 ` Bjorn Helgaas
2022-02-14 13:20 ` Francesco Dolcini
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