net: stmmac: dwmac-loongson: Add Loongson Multi-channels GMAC support

net: stmmac: dwmac-loongson: Add Loongson Multi-channels GMAC support

The Loongson DWMAC driver currently supports the Loongson GMAC
devices (based on the DW GMAC v3.50a/v3.73a IP-core) installed to the
LS2K1000 SoC and LS7A1000 chipset. But recently a new generation
LS2K2000 SoC was released with the new version of the Loongson GMAC
synthesized in. The new controller is based on the DW GMAC v3.73a
IP-core with the AV-feature enabled, which implies the multi
DMA-channels support. The multi DMA-channels feature has the next
vendor-specific peculiarities:

1. Split up Tx and Rx DMA IRQ status/mask bits:
       Name              Tx          Rx
  DMA_INTR_ENA_NIE = 0x00040000 | 0x00020000;
  DMA_INTR_ENA_AIE = 0x00010000 | 0x00008000;
  DMA_STATUS_NIS   = 0x00040000 | 0x00020000;
  DMA_STATUS_AIS   = 0x00010000 | 0x00008000;
  DMA_STATUS_FBI   = 0x00002000 | 0x00001000;
2. Custom Synopsys ID hardwired into the GMAC_VERSION.SNPSVER register
field. It's 0x10 while it should have been 0x37 in accordance with
the actual DW GMAC IP-core version.
3. There are eight DMA-channels available meanwhile the Synopsys DW
GMAC IP-core supports up to three DMA-channels.
4. It's possible to have each DMA-channel IRQ independently delivered.
The MSI IRQs must be utilized for that.

Thus in order to have the multi-channels Loongson GMAC controllers
supported let's modify the Loongson DWMAC driver in accordance with
all the peculiarities described above:

1. Create the multi-channels Loongson GMAC-specific
   stmmac_dma_ops::dma_interrupt()
   stmmac_dma_ops::init_chan()
   callbacks due to the non-standard DMA IRQ CSR flags layout.
2. Create the Loongson DWMAC-specific platform setup() method
which gets to initialize the DMA-ops with the dwmac1000_dma_ops
instance and overrides the callbacks described in 1. The method also
overrides the custom Synopsys ID with the real one in order to have
the rest of the HW-specific callbacks correctly detected by the driver
core.
3. Make sure the platform setup() method enables the flow control and
duplex modes supported by the controller.

Signed-off-by: Feiyang Chen <chenfeiyang@loongson.cn>
Signed-off-by: Yinggang Gu <guyinggang@loongson.cn>
Acked-by: Huacai Chen <chenhuacai@loongson.cn>
Signed-off-by: Yanteng Si <siyanteng@loongson.cn>
Reviewed-by: Serge Semin <fancer.lancer@gmail.com>
Tested-by: Serge Semin <fancer.lancer@gmail.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>