linux-kernel - Re: [PATCH V10 8/9] cxl/port: Retry reading CDAT on failure

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Date:   Wed, 8 Jun 2022 16:07:12 -0700
From:   Ira Weiny <ira.weiny@...el.com>
To:     Ben Widawsky <bwidawsk@...nel.org>
CC:     Dan Williams <dan.j.williams@...el.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Jonathan Cameron <Jonathan.Cameron@...wei.com>,
        Alison Schofield <alison.schofield@...el.com>,
        Davidlohr Bueso <dave@...olabs.net>,
        Vishal Verma <vishal.l.verma@...el.com>,
        Dave Jiang <dave.jiang@...el.com>,
        <linux-kernel@...r.kernel.org>, <linux-cxl@...r.kernel.org>,
        <linux-pci@...r.kernel.org>
Subject: Re: [PATCH V10 8/9] cxl/port: Retry reading CDAT on failure

On Mon, Jun 06, 2022 at 11:52:03AM -0700, Ben Widawsky wrote:
> On 22-06-04 17:50:48, ira.weiny@...el.com wrote:
> > From: Ira Weiny <ira.weiny@...el.com>
> > 
> > The CDAT read may fail for a number of reasons but mainly it is possible
> > to get different parts of a valid state.  The checksum in the CDAT table
> > protects against this.
> > 
> > Now that the cdat data is validated issue a retries if the CDAT read
> s/validated issue a retries/validated, issue a retry/

Thanks!

> > fails.  For now 5 retries are implemented.
> > 
> > Cc: Alison Schofield <alison.schofield@...el.com>
> > Cc: Davidlohr Bueso <dave@...olabs.net>
> > Signed-off-by: Ira Weiny <ira.weiny@...el.com>
> > 
> > ---
> > Changes from V9
> > 	Alison Schofield/Davidlohr Bueso
> > 		Print debug on each iteration and error only after failure
> > 
> > Changes from V8
> > 	Move code to cxl/core/pci.c
> > 
> > Changes from V6
> > 	Move to pci.c
> > 	Fix retries count
> > 	Change to 5 retries
> > 
> > Changes from V5:
> > 	New patch -- easy to push off or drop.
> > ---
> >  drivers/cxl/core/pci.c | 34 +++++++++++++++++++++++-----------
> >  1 file changed, 23 insertions(+), 11 deletions(-)
> > 
> > diff --git a/drivers/cxl/core/pci.c b/drivers/cxl/core/pci.c
> > index 73e28b82ffcf..e68f13e66fcf 100644
> > --- a/drivers/cxl/core/pci.c
> > +++ b/drivers/cxl/core/pci.c
> > @@ -631,20 +631,18 @@ static int cxl_cdat_read_table(struct cxl_port *port,
> >  	return rc;
> >  }
> >  
> > -void read_cdat_data(struct cxl_port *port)
> > +static int __read_cdat_data(struct cxl_port *port)
> >  {
> >  	struct device *dev = &port->dev;
> >  	size_t cdat_length;
> >  	int ret;
> >  
> >  	if (cxl_cdat_get_length(port, &cdat_length))
> > -		return;
> > +		return 0;
> >  
> >  	port->cdat.table = devm_kzalloc(dev, cdat_length, GFP_KERNEL);
> > -	if (!port->cdat.table) {
> > -		ret = -ENOMEM;
> > -		goto error;
> > -	}
> > +	if (!port->cdat.table)
> > +		return -ENOMEM;
> >  
> >  	port->cdat.length = cdat_length;
> >  	ret = cxl_cdat_read_table(port, &port->cdat);
> > @@ -652,12 +650,26 @@ void read_cdat_data(struct cxl_port *port)
> >  		devm_kfree(dev, port->cdat.table);
> >  		port->cdat.table = NULL;
> >  		port->cdat.length = 0;
> > -		ret = -EIO;
> > -		goto error;
> > +		return -EIO;
> >  	}
> >  
> > -	return;
> > -error:
> > -	dev_err(dev, "CDAT data read error (%d)\n", ret);
> > +	return 0;
> > +}
> > +
> > +void read_cdat_data(struct cxl_port *port)
> > +{
> > +	int retries = 5;
> > +	int rc;
> > +
> > +	while (retries--) {
> > +		rc = __read_cdat_data(port);
> > +		if (!rc)
> > +			return;
> > +		dev_dbg(&port->dev,
> > +			"CDAT data read error rc=%d (retries %d)\n",
> > +			rc, retries);
> 
> Out of curiousity, what is the purpose of the dev_dbg? To diagnose delays or
> something?

Yes

> 
> > +	}
> > +	dev_err(&port->dev, "CDAT data read failed after %d retries\n",
> > +		retries);
> 
> 
> Reviewed-by: Ben Widawsky <bwidawsk@...nel.org>

Thanks!
Ira

> 
> >  }
> >  EXPORT_SYMBOL_NS_GPL(read_cdat_data, CXL);
> > -- 
> > 2.35.1
> >