Hello,
kept exploring the sources of rtl8139 NIC and stuck with the weird spot in
'rtl8139_hw_start()' (same both in a 2.4.x and 2.6.x). I don't post here
very detailed code, as I assume everybody here has access to linux source
tree:
...
/* init Tx buffer DMA addresses */
for (i = 0; i < NUM_TX_DESC; i++)
RTL_W32_F (TxAddr0 + (i * 4), tp->tx_bufs_dma + (tp->tx_buf[i] -
tp->tx_bufs));
RTL_W32_F is a macro exposing into:
'writel(tp->tx_bufs_dma + (tp->tx_buf[i] - tp->tx_bufs), ...)'
By the time of this call 'tx_buf' has been properly initialised and contains
addresses of 4 TX descriptors.
As I understand 'tx_bufs_dma' holds the physical address of DMA memory,
while 'tx_bufs' - kernel virtual address. What I can't figure out is the
point of this calculations: tp->tx_bufs_dma + (tp->tx_buf[i] - tp->tx_bufs)
Why can't we simply have 'tp->tx_bufs_dma + (i * 4)', providing that we know
the size of TX descriptors is 32 bits ?
Thanks in advance.
--
Roman Mashak
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