The GCE in MT8196 is placed in MMINFRA and requires all addresses
in GCE instructions for DRAM transactions to be IOVA.
Due to MMIO, if the GCE needs to access a hardware register at
0x1000_0000, but the SMMU is also mapping a DRAM block at 0x1000_0000,
the MMINFRA will not know whether to write to the hardware register or
the DRAM.
To solve this, MMINFRA treats addresses greater than 2G as data paths
and those less than 2G as config paths because the DRAM start address
is currently at 2G (0x8000_0000). On the data path, MMINFRA remaps
DRAM addresses by subtracting 2G, allowing SMMU to map DRAM addresses
less than 2G.
For example, if the DRAM start address 0x8000_0000 is mapped to
IOVA=0x0, when GCE accesses IOVA=0x0, it must add a 2G offset to
the address in the GCE instruction. MMINFRA will then see it as a
data path (IOVA >= 2G) and subtract 2G, allowing GCE to access IOVA=0x0.
Since the MMINFRA remap subtracting 2G is done in hardware and cannot
be configured by software, the address of DRAM in GCE instruction must
always add 2G to ensure proper access. After that, the shift functions
do more than just shift addresses, so the APIs were renamed to
cmdq_convert_gce_addr() and cmdq_revert_gce_addr().
This 2G adjustment is referred to as mminfra_offset in the CMDQ driver.
CMDQ helper can get the mminfra_offset from the cmdq_mbox_priv of
cmdq_pkt and add the mminfra_offset to the DRAM address in GCE
instructions.
Signed-off-by: Jason-JH Lin <jason-jh.lin@mediatek.com>
Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Signed-off-by: Jassi Brar <jassisinghbrar@gmail.com>
