netdev - Re: [PATCH 3/6] bus: fsl-mc: return -EPROBE_DEFER when a device is not yet discovered

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Date:   Thu, 7 Jan 2021 19:15:51 +0200
From:   Laurentiu Tudor <laurentiu.tudor@....com>
To:     Ioana Ciornei <ciorneiioana@...il.com>, davem@...emloft.net,
        kuba@...nel.org, netdev@...r.kernel.org
Cc:     Ioana Ciornei <ioana.ciornei@....com>
Subject: Re: [PATCH 3/6] bus: fsl-mc: return -EPROBE_DEFER when a device is
 not yet discovered


On 1/7/2021 5:36 PM, Ioana Ciornei wrote:
> From: Ioana Ciornei <ioana.ciornei@....com>
> 
> The fsl_mc_get_endpoint() should return a pointer to the connected
> fsl_mc device, if there is one. By interrogating the MC firmware, we
> know if there is an endpoint or not so when the endpoint device is
> actually searched on the fsl-mc bus and not found we are hitting the
> case in which the device has not been yet discovered by the bus.
> 
> Return -EPROBE_DEFER so that callers can differentiate this case.
> 
> Signed-off-by: Ioana Ciornei <ioana.ciornei@....com>

Acked-by: Laurentiu Tudor <laurentiu.tudor@....com>

---
Best Regards, Laurentiu

> ---
>  drivers/bus/fsl-mc/fsl-mc-bus.c | 9 +++++++++
>  1 file changed, 9 insertions(+)
> 
> diff --git a/drivers/bus/fsl-mc/fsl-mc-bus.c b/drivers/bus/fsl-mc/fsl-mc-bus.c
> index 34811db074b7..28d5da1c011c 100644
> --- a/drivers/bus/fsl-mc/fsl-mc-bus.c
> +++ b/drivers/bus/fsl-mc/fsl-mc-bus.c
> @@ -936,6 +936,15 @@ struct fsl_mc_device *fsl_mc_get_endpoint(struct fsl_mc_device *mc_dev)
>  	endpoint_desc.id = endpoint2.id;
>  	endpoint = fsl_mc_device_lookup(&endpoint_desc, mc_bus_dev);
>  
> +	/*
> +	 * We know that the device has an endpoint because we verified by
> +	 * interrogating the firmware. This is the case when the device was not
> +	 * yet discovered by the fsl-mc bus, thus the lookup returned NULL.
> +	 * Differentiate this case by returning EPROBE_DEFER.
> +	 */
> +	if (!endpoint)
> +		return ERR_PTR(-EPROBE_DEFER);
> +
>  	return endpoint;
>  }
>  EXPORT_SYMBOL_GPL(fsl_mc_get_endpoint);
>