From: Lukas Wunner <lukas@wunner.de>
To: Sanjay R Mehta <Sanju.Mehta@amd.com>
Cc: bhelgaas@google.com, andriy.shevchenko@linux.intel.com,
stuart.w.hayes@gmail.com, mr.nuke.me@gmail.com,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH] PCI: pciehp: Add check for DL_ACTIVE bit in pciehp_check_link_status()
Date: Tue, 6 Oct 2020 21:38:30 +0200 [thread overview]
Message-ID: <20201006193830.GA32510@wunner.de> (raw)
In-Reply-To: <1602008668-43646-1-git-send-email-Sanju.Mehta@amd.com>
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?
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
next prev parent reply other threads:[~2020-10-06 19:38 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-10-06 18:24 [PATCH] PCI: pciehp: Add check for DL_ACTIVE bit in pciehp_check_link_status() Sanjay R Mehta
2020-10-06 19:38 ` Lukas Wunner [this message]
2020-10-08 7:13 ` Sanjay R Mehta
2020-10-08 11:29 ` Andy Shevchenko
2020-10-09 10:34 ` Lukas Wunner
2020-10-07 9:30 ` [kbuild] " Dan Carpenter
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