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Unlike gmac100, gmac1000, gmac4 has 27 DMA registers and they are
located at DMA_CHAN_BASE_ADDR (0x1100). In order for ethtool to dump
gmac4 DMA registers correctly, this commit checks if a net_device has
gmac4 and uses different logic to dump its DMA registers.

This fixes the following KASAN warning, which can normally be triggered
by a command similar like "ethtool -d eth0":

BUG: KASAN: vmalloc-out-of-bounds in dwmac4_dump_dma_regs+0x6d4/0xb30
Write of size 4 at addr ffffffc010177100 by task ethtool/1839
 kasan_report+0x200/0x21c
 __asan_report_store4_noabort+0x34/0x60
 dwmac4_dump_dma_regs+0x6d4/0xb30
 stmmac_ethtool_gregs+0x110/0x204
 ethtool_get_regs+0x200/0x4b0
 dev_ethtool+0x1dac/0x3800
 dev_ioctl+0x7c0/0xb50
 sock_ioctl+0x298/0x6c4
 ...

Fixes: fbf68229

 ("net: stmmac: unify registers dumps methods")
Signed-off-by: Camel Guo <camelg@axis.com>
Link: https://lore.kernel.org/r/20220131083841.3346801-1-camel.guo@axis.com

Signed-off-by: Jakub Kicinski <kuba@kernel.org>