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Date:   Wed, 23 Nov 2016 15:12:21 +0000
From:   Hayes Wang <hayeswang@...ltek.com>
To:     Mark Lord <mlord@...ox.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>
CC:     nic_swsd <nic_swsd@...ltek.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>
Subject: RE: [PATCH net 1/2] r8152: fix the sw rx checksum is unavailable

Mark Lord [mlord@...ox.com]
[...]
> What does this code do:

> >static void r8153_set_rx_early_size(struct r8152 *tp)
> >{
> >        u32 mtu = tp->netdev->mtu;
> >        u32 ocp_data = (agg_buf_sz - mtu - VLAN_ETH_HLEN - VLAN_HLEN) / 4;
> >
> >        ocp_write_word(tp, MCU_TYPE_USB, USB_RX_EARLY_SIZE, ocp_data);
> >}

This only works for RTL8153. However, what you use is RTL8152.
It is like delay completion. It is used to reduce the loading of CPU
by letting a transfer contain more data to reduce the number of
transfers.

> How is ocp_data used by the hardware?
> Shouldn't the calculation also include sizeof(rx_desc) in there somewhere?

The algorithm is from our hw engineers, and it should be 

   (agg_buf_sz - packet size) / 8

You could refer to commit a59e6d815226 ("r8152: correct the rx early size").

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