Re: [PATCH] PCI: pciehp: Add check for DL_ACTIVE bit in pciehp_check_link_status()

Sanjay R Mehta
2020-10-08T07:13:31Z

On 10/7/2020 1:08 AM, Lukas Wunner wrote:
> [CAUTION: External Email]
>
> On Tue, Oct 06, 2020 at 01:24:28PM -0500, Sanjay R Mehta wrote:
>> if DL_ACTIVE bit is set it means that there is no need to check
>> PCI_EXP_LNKSTA_LT bit, as DL_ACTIVE would have set only if the link
>> is already trained. Hence adding a check which takes care of this
>> scenario.
>
> Sorry for being dense but I don't understand this at all:
>
> The PCI_EXP_DPC_CAP_DL_ACTIVE bit which you check here indicates
> that the port is capable of sending an ERR_COR interrupt whenever
> the link transitions from inactive to active.
>
> What is the connection to the PCI_EXP_LNKSTA_LT bit (which indicates
> that the link is still being trained)?
>
> Also, the negation of a bitwise AND is always either 0 or 1
> (!(lnk_status & PCI_EXP_DPC_CAP_DL_ACTIVE)), so bit 0 is set or not set.
> However PCI_EXP_LNKSTA_LT is bit 11. A bitwise AND of bit 11 and 0 is
> always 0, so the expression can never be 1.
>
> Am I missing something?
>
Please accept my sincere apologies for sending the wrong patch.

I am supposed to use PCI_EXP_LNKSTA_DLLLA bit in my patch but have used PCI_EXP_DPC_CAP_DL_ACTIVE.

The correct code should be as below,

- if ((lnk_status & PCI_EXP_LNKSTA_LT) ||
+ if (((lnk_status & PCI_EXP_LNKSTA_LT) &
+ !(lnk_status & PCI_EXP_LNKSTA_DLLLA )) ||

Is it right? please share your feedback, if I am wrong. Will send out V2 patch, once you confirm on this.

> Thanks,
>
> Lukas
>
>> Signed-off-by: Sanjay R Mehta <sanju.mehta@amd.com>
>> ---
>> drivers/pci/hotplug/pciehp_hpc.c | 3 ++-
>> 1 file changed, 2 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/pci/hotplug/pciehp_hpc.c b/drivers/pci/hotplug/pciehp_hpc.c
>> index 53433b3..81d1348 100644
>> --- a/drivers/pci/hotplug/pciehp_hpc.c
>> +++ b/drivers/pci/hotplug/pciehp_hpc.c
>> @@ -309,7 +309,8 @@ int pciehp_check_link_status(struct controller *ctrl)
>>
>> pcie_capability_read_word(pdev, PCI_EXP_LNKSTA, &lnk_status);
>> ctrl_dbg(ctrl, "%s: lnk_status = %x\n", __func__, lnk_status);
>> - if ((lnk_status & PCI_EXP_LNKSTA_LT) ||
>> + if (((lnk_status & PCI_EXP_LNKSTA_LT) &
>> + !(lnk_status & PCI_EXP_DPC_CAP_DL_ACTIVE)) ||
>> !(lnk_status & PCI_EXP_LNKSTA_NLW)) {
>> ctrl_err(ctrl, "link training error: status %#06x\n",
>> lnk_status);
>> --
>> 2.7.4