On Monday 30 November 2020 10:52:00 Lorenzo Pieralisi wrote: > On Mon, Nov 30, 2020 at 12:17:41AM +0100, Pali Rohár wrote: > > On Sunday 11 October 2020 19:21:49 Pali Rohár wrote: > > > On Thursday 24 September 2020 17:22:32 Pali Rohár wrote: > > > > On Thursday 24 September 2020 10:11:06 Bjorn Helgaas wrote: > > > > > On Thu, Sep 24, 2020 at 10:46:18AM +0200, Pali Rohár wrote: > > > > > > It is not HW bug or workaround for some cards but it is requirement by PCI > > > > > > Express spec. After fundamental reset is needed 100ms delay prior enabling > > > > > > link training. So update comment in code to reflect this requirement. > > > > > > > > > > > > Signed-off-by: Pali Rohár <pali@xxxxxxxxxx> > > > > > > --- > > > > > > drivers/pci/controller/pci-aardvark.c | 7 ++++++- > > > > > > 1 file changed, 6 insertions(+), 1 deletion(-) > > > > > > > > > > > > diff --git a/drivers/pci/controller/pci-aardvark.c b/drivers/pci/controller/pci-aardvark.c > > > > > > index 50ab6d7519ae..19b9b79226e5 100644 > > > > > > --- a/drivers/pci/controller/pci-aardvark.c > > > > > > +++ b/drivers/pci/controller/pci-aardvark.c > > > > > > @@ -259,7 +259,12 @@ static void advk_pcie_issue_perst(struct advk_pcie *pcie) > > > > > > if (!pcie->reset_gpio) > > > > > > return; > > > > > > > > > > > > - /* PERST does not work for some cards when link training is enabled */ > > > > > > + /* > > > > > > + * As required by PCI Express spec a delay for at least 100ms after > > > > > > + * de-asserting PERST# signal is needed before link training is enabled. > > > > > > + * So ensure that link training is disabled prior de-asserting PERST# > > > > > > + * signal to fulfill that PCI Express spec requirement. > > > > > > > > > > Can you please include the spec citation here? In the PCIe base spec, > > > > > PERST# is only mentioned in PCIe r5.0, sec 6.6.1, and I don't see the > > > > > connection there to 100ms between de-assert of PERST# and enabling > > > > > link training. > > > > > > > > Hello! I copied this "comment" from other place in pci-aardvark.c where > > > > that timeout 100ms is already applied. Timeout with explanation comment > > > > was introduced in following commit: > > > > > > > > https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=f4c7d053d7f7 > > > > > > > > Here are links to discussions about that patch: > > > > > > > > https://lore.kernel.org/linux-pci/20190313213752.1246-1-repk@xxxxxxxxxxxx/T/#u > > > > https://lore.kernel.org/linux-pci/20190522213351.21366-2-repk@xxxxxxxxxxxx/T/#u > > > > > > Bjorn or Lorenzo, do you need something else for this patch? It just > > > updates comment and basically clarify why PERST does not work for some > > > cards when link training is enabled. > > > > PING? > > Apologies, I marked it as "changes requested" following Bjorn's reply. > Would you mind please adding a link to the relevant PCI specs in the > comment ? Of course, no problem. I will copy reference to PCI spec as Remi wrote it in linked email, to the comment in source code. > I understood you copied the comment, it is worth adding that link to all > of them if you don't mind, it can be a preparation patch if you wish. > > Thanks, > Lorenzo > > > > > > Sec 6.1.1 does talk about 100ms before sending config requests (for > > > > > ports that support <= 5 GT/s), and 100ms after link training completes > > > > > (for ports that support > 5 GT/s). > > > > > > > > > > Maybe there's more language in a form-factor spec or something? > > > > > > > > > > > + */ > > > > > > reg = advk_readl(pcie, PCIE_CORE_CTRL0_REG); > > > > > > reg &= ~LINK_TRAINING_EN; > > > > > > advk_writel(pcie, reg, PCIE_CORE_CTRL0_REG); > > > > > > -- > > > > > > 2.20.1 > > > > > >
