| Message ID | 20220211152550.286821-1-francesco.dolcini@toradex.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | [v1] PCI: imx6: Fix PERST# start-up sequence | expand |
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 >
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
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:
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(-)