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Date:   Mon, 3 Aug 2020 10:16:04 +0200
From:   Greg KH <gregkh@...uxfoundation.org>
To:     yzc666@...ease.com
Cc:     bjorn@...k.no, davem@...emloft.net, kuba@...nel.org,
        netdev@...r.kernel.org, linux-usb@...r.kernel.org,
        carl <carl.yin@...ctel.com>
Subject: Re: [PATCH]     qmi_wwan: support modify usbnet's rx_urb_size

On Mon, Aug 03, 2020 at 02:51:05PM +0800, yzc666@...ease.com wrote:
> From: carl <carl.yin@...ctel.com>
> 
>     When QMUX enabled, the 'dl-datagram-max-size' can be 4KB/16KB/31KB depend on QUALCOMM's chipsets.
>     User can set 'dl-datagram-max-size' by 'QMI_WDA_SET_DATA_FORMAT'.
>     The usbnet's rx_urb_size must lager than or equal to the 'dl-datagram-max-size'.
>     This patch allow user to modify usbnet's rx_urb_size by next command.
> 
> 		echo 4096 > /sys/class/net/wwan0/qmi/rx_urb_size
> 
> 		Next commnds show how to set and query 'dl-datagram-max-size' by qmicli
> 		# qmicli -d /dev/cdc-wdm1 --wda-set-data-format="link-layer-protocol=raw-ip, ul-protocol=qmap,
> 				dl-protocol=qmap, dl-max-datagrams=32, dl-datagram-max-size=31744, ep-type=hsusb, ep-iface-number=4"
> 		[/dev/cdc-wdm1] Successfully set data format
> 		                        QoS flow header: no
> 		                    Link layer protocol: 'raw-ip'
> 		       Uplink data aggregation protocol: 'qmap'
> 		     Downlink data aggregation protocol: 'qmap'
> 		                          NDP signature: '0'
> 		Downlink data aggregation max datagrams: '10'
> 		     Downlink data aggregation max size: '4096'
> 
> 	    # qmicli -d /dev/cdc-wdm1 --wda-get-data-format
> 		[/dev/cdc-wdm1] Successfully got data format
> 		                   QoS flow header: no
> 		               Link layer protocol: 'raw-ip'
> 		  Uplink data aggregation protocol: 'qmap'
> 		Downlink data aggregation protocol: 'qmap'
> 		                     NDP signature: '0'
> 		Downlink data aggregation max datagrams: '10'
> 		Downlink data aggregation max size: '4096'
> 
> Signed-off-by: carl <carl.yin@...ctel.com>
> ---
>  drivers/net/usb/qmi_wwan.c | 39 ++++++++++++++++++++++++++++++++++++++
>  1 file changed, 39 insertions(+)
> 
> diff --git a/drivers/net/usb/qmi_wwan.c b/drivers/net/usb/qmi_wwan.c
> index 07c42c0719f5b..8ea57fd99ae43 100644
> --- a/drivers/net/usb/qmi_wwan.c
> +++ b/drivers/net/usb/qmi_wwan.c
> @@ -400,6 +400,44 @@ static ssize_t raw_ip_store(struct device *d,  struct device_attribute *attr, co
>  	return ret;
>  }
>  
> +static ssize_t rx_urb_size_show(struct device *d, struct device_attribute *attr, char *buf)
> +{
> +	struct usbnet *dev = netdev_priv(to_net_dev(d));
> +
> +	return sprintf(buf, "%zd\n", dev->rx_urb_size);

Why do you care about this?

> +}
> +
> +static ssize_t rx_urb_size_store(struct device *d,  struct device_attribute *attr,
> +				 const char *buf, size_t len)
> +{
> +	struct usbnet *dev = netdev_priv(to_net_dev(d));
> +	u32 rx_urb_size;
> +	int ret;
> +
> +	if (kstrtou32(buf, 0, &rx_urb_size))
> +		return -EINVAL;
> +
> +	/* no change? */
> +	if (rx_urb_size == dev->rx_urb_size)
> +		return len;
> +
> +	if (!rtnl_trylock())
> +		return restart_syscall();
> +
> +	/* we don't want to modify a running netdev */
> +	if (netif_running(dev->net)) {
> +		netdev_err(dev->net, "Cannot change a running device\n");
> +		ret = -EBUSY;
> +		goto err;
> +	}
> +
> +	dev->rx_urb_size = rx_urb_size;
> +	ret = len;
> +err:
> +	rtnl_unlock();
> +	return ret;
> +}
> +
>  static ssize_t add_mux_show(struct device *d, struct device_attribute *attr, char *buf)
>  {
>  	struct net_device *dev = to_net_dev(d);
> @@ -505,6 +543,7 @@ static DEVICE_ATTR_RW(add_mux);
>  static DEVICE_ATTR_RW(del_mux);
>  
>  static struct attribute *qmi_wwan_sysfs_attrs[] = {
> +	&dev_attr_rx_urb_size.attr,

You added a driver-specific sysfs file and did not document in in
Documentation/ABI?  That's not ok, sorry, please fix up.

Actually, no, this all should be done "automatically", do not change the
urb size on the fly.  Change it at probe time based on the device you
are using, do not force userspace to "know" what to do here, as it will
not know that at all.

thanks,

greg k-h

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