linux-kernel - Re: [PATCH] PCI: pciehp: Add check for DL_ACTIVE bit in pciehp_check_link

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Message-ID: <20201008112904.GH4077@smile.fi.intel.com>
Date:   Thu, 8 Oct 2020 14:29:04 +0300
From:   Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:     Sanjay R Mehta <sanmehta@....com>
Cc:     Lukas Wunner <lukas@...ner.de>,
        Sanjay R Mehta <Sanju.Mehta@....com>, bhelgaas@...gle.com,
        stuart.w.hayes@...il.com, mr.nuke.me@...il.com,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] PCI: pciehp: Add check for DL_ACTIVE bit in
 pciehp_check_link_status()

On Thu, Oct 08, 2020 at 12:43:17PM +0530, Sanjay R Mehta wrote:
> On 10/7/2020 1:08 AM, Lukas Wunner wrote:
> > 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.

At least you are ignoring LKP valid warning...

-- 
With Best Regards,
Andy Shevchenko