firmware: imx-dsp: Export functions to request/free channels

In order to save power, we only need to request a channel
when the communication with the DSP active.

For this we export the following functions:
	- imx_dsp_request_channel, gets a channel with a given index
	- imx_dsp_free_channel, frees a channel with a given index

Notice that we still request channels at probe to support devices
that do not have PM callbacks implemented.

More explanations about why requesting a channel has an effect
on power savings:
 - requesting an mailbox channel will call mailbox's startup
   function.
 - startup function calls pm_runtime_get_sync which increments device
   usage count and will keep the device active. Specifically, mailbox
   clock will be always ON when a mailbox channel is requested.

Signed-off-by: Daniel Baluta <daniel.baluta@nxp.com>
Reviewed-by: Paul Olaru <paul.olaru@nxp.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>

1 files changed, 10 insertions, 0 deletions

diff --git a/include/linux/firmware/imx/dsp.h b/include/linux/firmware/imx/dsp.h
index 7562099c9e46..4f7895a3b73c 100644
--- a/include/linux/firmware/imx/dsp.h
+++ b/include/linux/firmware/imx/dsp.h
@@ -55,6 +55,9 @@ static inline void *imx_dsp_get_data(struct imx_dsp_ipc *ipc)
 
 int imx_dsp_ring_doorbell(struct imx_dsp_ipc *dsp, unsigned int chan_idx);
 
+struct mbox_chan *imx_dsp_request_channel(struct imx_dsp_ipc *ipc, int idx);
+void imx_dsp_free_channel(struct imx_dsp_ipc *ipc, int idx);
+
 #else
 
 static inline int imx_dsp_ring_doorbell(struct imx_dsp_ipc *ipc,
@@ -63,5 +66,12 @@ static inline int imx_dsp_ring_doorbell(struct imx_dsp_ipc *ipc,
 	return -ENOTSUPP;
 }
 
+struct mbox_chan *imx_dsp_request_channel(struct imx_dsp_ipc *ipc, int idx)
+{
+	return ERR_PTR(-EOPNOTSUPP);
+}
+
+void imx_dsp_free_channel(struct imx_dsp_ipc *ipc, int idx) { }
+
 #endif
 #endif /* _IMX_DSP_IPC_H */