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

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Date:   Mon, 6 Jun 2022 11:52:03 -0700
From:   Ben Widawsky <bwidawsk@...nel.org>
To:     ira.weiny@...el.com
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 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/
> 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?

> +	}
> +	dev_err(&port->dev, "CDAT data read failed after %d retries\n",
> +		retries);


Reviewed-by: Ben Widawsky <bwidawsk@...nel.org>

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