Messages in this thread | | | Date | Thu, 01 Aug 2013 17:29:28 -0400 | From | Don Dutile <> | Subject | Re: [PATCH v3 8/9] pci: Tune secondary bus reset timing |
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On 08/01/2013 12:55 PM, Alex Williamson wrote: > The PCI spec indicates that with stable power, reset needs to be > asserted for a minimum of 1ms (Trst). Seems like we should be able > to assume power is stable for a runtime secondary bus reset. The > current code has always used 100ms with no explanation where that > came from. The aer_do_secondary_bus_reset() function uses 2ms, but > that seems to be a misinterpretation of the PCIe spec, where hot > reset is implemented by TS1 ordered sets containing the hot reset > command. After a 2ms delay the state machine enters the detect state, > but to generate a link down, only two consecutive TS1 hot reset > ordered sets are requred. 1ms should be plenty for that. > > After reset is de-asserted we must wait for devices to complete > initialization. The specs refer to this as "recovery time" (Trhfa). > For PCI this is 2^25 clock cycles or 2^26 for PCI-X. For minimum > bus speeds, both of those come to 1s. PCIe "softens" this > requirement with the Configuration Request Retry Status (CRS) > completion status. Theoretically we could use CRS to shorten the > wait time. We don't make use of that here, using a fixed 1s delay > to allow devices to re-initialize. Unfortunately, I don't think CRS is widely supported to make it worth the additional checking & use, atm.
> > Signed-off-by: Alex Williamson<alex.williamson@redhat.com> > --- > drivers/pci/pci.c | 15 +++++++++++++-- > 1 file changed, 13 insertions(+), 2 deletions(-) > > diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c > index 3e71887..a5c6a9b 100644 > --- a/drivers/pci/pci.c > +++ b/drivers/pci/pci.c > @@ -3291,11 +3291,22 @@ void pci_reset_bridge_secondary_bus(struct pci_dev *dev) > pci_read_config_word(dev, PCI_BRIDGE_CONTROL,&ctrl); > ctrl |= PCI_BRIDGE_CTL_BUS_RESET; > pci_write_config_word(dev, PCI_BRIDGE_CONTROL, ctrl); > - msleep(100); > + /* > + * PCI spec v3.0 7.6.4.2 requires minimum Trst of 1ms. > + */ > + msleep(1); > > ctrl&= ~PCI_BRIDGE_CTL_BUS_RESET; > pci_write_config_word(dev, PCI_BRIDGE_CONTROL, ctrl); > - msleep(100); > + > + /* > + * Trhfa for conventional PCI is 2^25 clock cycles. > + * Assuming a minimum 33MHz clock this results in a 1s > + * delay before we can consider subordinate devices to > + * be re-initialized. PCIe has some ways to shorten this, > + * but we don't make use of them yet. > + */ > + ssleep(1); Can't bus speed be determined from (config space) status bits, so this time can be minimized, esp. on modern, PCIe busses/links ? Not too many 33Mhz, legacy PCI busses that this type of timing is desired, or will be done to (for device assignment/vfio). :-/
> } > EXPORT_SYMBOL_GPL(pci_reset_bridge_secondary_bus); > > > -- > To unsubscribe from this list: send the line "unsubscribe linux-pci" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html
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