linux-kernel - Re: [PATCH V14 3/7] PCI/DOE: Add DOE mailbox support functions

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Date:   Tue, 19 Jul 2022 12:50:56 -0700
From:   Ira Weiny <ira.weiny@...el.com>
To:     Jonathan Cameron <Jonathan.Cameron@...wei.com>
CC:     Dan Williams <dan.j.williams@...el.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        "Li, Ming" <ming4.li@...el.com>,
        Bjorn Helgaas <helgaas@...nel.org>,
        Matthew Wilcox <willy@...radead.org>,
        Lukas Wunner <lukas@...ner.de>,
        Alison Schofield <alison.schofield@...el.com>,
        "Vishal Verma" <vishal.l.verma@...el.com>,
        Dave Jiang <dave.jiang@...el.com>,
        "Ben Widawsky" <bwidawsk@...nel.org>,
        <linux-kernel@...r.kernel.org>, <linux-cxl@...r.kernel.org>,
        <linux-pci@...r.kernel.org>
Subject: Re: [PATCH V14 3/7] PCI/DOE: Add DOE mailbox support functions

On Tue, Jul 19, 2022 at 12:16:06PM -0700, Ira wrote:
> On Tue, Jul 19, 2022 at 05:35:53PM +0100, Jonathan Cameron wrote:
[snip]

> > Hi Ira,
> > 
> > Thanks for persisting with this!
> > 
> > So, I think this works, but there is at least one 'sleep' I can't
> > see a purpose for.  I think it's just a left over from refactoring.
> > 
> > A few other more trivial things inline.

[snip]

> > > +
> > > +#define PCI_DOE_BUSY_MAX_RETRIES 16
> > Left over from removed code.
> 
> I think Dan may have taken these.  If so I'll send a clean up.  If not I can
> spin.  Let me check.

I'm spinning a v15 of this patch.

[snip]

> 
> > 
> > > +	if (rc) {
> > > +		/*
> > > +		 * The specification does not provide any guidance on how to
> > > +		 * resolve conflicting requests from other entities.
> > > +		 * Furthermore, it is likely that busy will not be detected
> > > +		 * most of the time.  Flag any detection of status busy with an
> > > +		 * error.
> > > +		 */
> > > +		if (rc == -EBUSY)
> > > +			dev_err_ratelimited(&pdev->dev, "[%x] busy detected; another entity is sending conflicting requests\n",
> > > +					    offset);
> > > +		signal_task_abort(task, rc);
> > > +		return;
> > > +	}
> > > +
> > > +	timeout_jiffies = jiffies + PCI_DOE_TIMEOUT;
> > > +	rc = pci_doe_wait(doe_mb, PCI_DOE_POLL_INTERVAL);
> > 
> > What's this particular wait for?  I think you can just move directly to checking
> > if the response is ready.
> 
> We could but I assume it will take at least some time to process the request.
> So it seemed best to wait and then check.
> 
> But of course we all know that also used to wait for an IRQ as an option.  :-/
> 
> I'm really on the fence here because I don't think it really matters.  We are
> sleeping so it does not really affect the system much and this is not a
> performance path.  If we were spinning I would agree with you.

I've deferred to your expertise here and removed the extra wait.

Ira