mailbox: mtk-cmdq: Refine DMA address handling for the command buffer

[ Upstream commit a195c7ccfb7a21b8118139835e25936ec8722596 ]

GCE can only fetch the command buffer address from a 32-bit register.
Some SoCs support a 35-bit command buffer address for GCE, which
requires a right shift of 3 bits before setting the address into
the 32-bit register. A comment has been added to the header of
cmdq_get_shift_pa() to explain this requirement.

To prevent the GCE command buffer address from being DMA mapped beyond
its supported bit range, the DMA bit mask for the device is set during
initialization.

Additionally, to ensure the correct shift is applied when setting or
reading the register that stores the GCE command buffer address,
new APIs, cmdq_convert_gce_addr() and cmdq_revert_gce_addr(), have
been introduced for consistent operations on this register.

The variable type for the command buffer address has been standardized
to dma_addr_t to prevent handling issues caused by type mismatches.

Fixes: 0858fde496f8 ("mailbox: cmdq: variablize address shift in platform")
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>
Signed-off-by: Sasha Levin <sashal@kernel.org>

1 files changed, 10 insertions, 0 deletions

diff --git a/include/linux/mailbox/mtk-cmdq-mailbox.h b/include/linux/mailbox/mtk-cmdq-mailbox.h
index a8f0070c7aa9..9914dcd33e2d 100644
--- a/include/linux/mailbox/mtk-cmdq-mailbox.h
+++ b/include/linux/mailbox/mtk-cmdq-mailbox.h
@@ -78,6 +78,16 @@ struct cmdq_pkt {
 	void			*cl;
 };
 
+/**
+ * cmdq_get_shift_pa() - get the shift bits of physical address
+ * @chan: mailbox channel
+ *
+ * GCE can only fetch the command buffer address from a 32-bit register.
+ * Some SOCs support more than 32-bit command buffer address for GCE, which
+ * requires some shift bits to make the address fit into the 32-bit register.
+ *
+ * Return: the shift bits of physical address
+ */
 u8 cmdq_get_shift_pa(struct mbox_chan *chan);
 
 #endif /* __MTK_CMDQ_MAILBOX_H__ */