Re: [PATCH v3 2/3] PCI: pciehp: Wait for PDS if in-band presence is disabled

Stuart Hayes
2019-10-21T18:08:05Z

On 10/21/19 8:41 AM, Mika Westerberg wrote:
> On Thu, Oct 17, 2019 at 03:32:55PM -0400, Stuart Hayes wrote:
>> From: Alexandru Gagniuc <mr.nuke.me@gmail.com>
>>
>> When inband presence is disabled, PDS may come up at any time, or not
>> at all. PDS being low may indicate that the card is still mating, and
>> we could expect contact bounce to bring down the link as well.
>>
>> It is reasonable to assume that most cards will mate in a hotplug slot
>> in about a second. Thus, when we know PDS only reflects out-of-band
>> presence, it's worthwhile to wait the extra second or so to make sure
>> the card is properly mated before loading the driver, and to prevent
>> the hotplug code from disabling a device if the presence detect change
>> goes active after the device is enabled.
>>
>> Signed-off-by: Alexandru Gagniuc <mr.nuke.me@gmail.com>
>> Signed-off-by: Stuart Hayes <stuart.w.hayes@gmail.com>
>
> Reviewed-by: Mika Westerberg <mika.westerberg@linux.intel.com>
>
> One nit below.
>
>> ---
>> v2:
>> replace while(true) loop with do...while
>> v3
>> remove unused variable declaration (pds)
>> modify text of warning message
>>
>> drivers/pci/hotplug/pciehp_hpc.c | 19 +++++++++++++++++++
>> 1 file changed, 19 insertions(+)
>>
>> diff --git a/drivers/pci/hotplug/pciehp_hpc.c b/drivers/pci/hotplug/pciehp_hpc.c
>> index dc109d521f30..02eb811a014f 100644
>> --- a/drivers/pci/hotplug/pciehp_hpc.c
>> +++ b/drivers/pci/hotplug/pciehp_hpc.c
>> @@ -242,6 +242,22 @@ static bool pci_bus_check_dev(struct pci_bus *bus, int devfn)
>> return found;
>> }
>>
>> +static void pcie_wait_for_presence(struct pci_dev *pdev)
>> +{
>> + int timeout = 1250;
>> + u16 slot_status;
>> +
>> + do {
>> + pcie_capability_read_word(pdev, PCI_EXP_SLTSTA, &slot_status);
>> + if (!!(slot_status & PCI_EXP_SLTSTA_PDS))
>
> It is more readable if you write it like:
>
> if (slot_status & PCI_EXP_SLTSTA_PDS)
>

I agree, it is more readable, and the double bang shouldn't be needed for an
"if" condition. Thanks.

>> + return;
>> + msleep(10);
>> + timeout -= 10;
>> + } while (timeout > 0);
>> +
>> + pci_info(pdev, "Timeout waiting for Presence Detect state to be set\n");
>> +}
>> +
>> int pciehp_check_link_status(struct controller *ctrl)
>> {
>> struct pci_dev *pdev = ctrl_dev(ctrl);
>> @@ -251,6 +267,9 @@ int pciehp_check_link_status(struct controller *ctrl)
>> if (!pcie_wait_for_link(pdev, true))
>> return -1;
>>
>> + if (ctrl->inband_presence_disabled)
>> + pcie_wait_for_presence(pdev);
>> +
>> found = pci_bus_check_dev(ctrl->pcie->port->subordinate,
>> PCI_DEVFN(0, 0));
>>
>> --
>> 2.18.1