[PATCH v7 06/16] firmware: arm_scmi: Add configurable polling mode for transports

Cristian Marussi
2021-11-29T19:16:34Z

SCMI communications along TX channels can optionally be provided of a
completion interrupt; when such interrupt is not available, command
transactions should rely on polling, where the SCMI core takes care to
repeatedly evaluate the transport-specific .poll_done() function, if
available, to determine if and when a request was fully completed or
timed out.

Such mechanism is already present and working on a single transfer base:
SCMI protocols can indeed enable hdr.poll_completion on specific commands
ahead of each transfer and cause that transaction to be handled with
polling.

Introduce a couple of flags to be able to enforce such polling behaviour
globally at will:

- scmi_desc.force_polling: to statically switch the whole transport to
polling mode.

- scmi_chan_info.no_completion_irq: to switch a single channel dynamically
to polling mode if, at runtime, is determined that no completion
interrupt was available for such channel.

Signed-off-by: Cristian Marussi <cristian.marussi@arm.com>
---
v5 --> v6
- removed check on replies received by IRQs when xfer was requested
as poll_completion (not all transport can suppress IRQs on an xfer basis)
v4 --> v5
- make force_polling const
- introduce polling_enabled flag to simplify checks on do_xfer
v3 --> v4:
- renamed .needs_polling flag to .no_completion_irq
- refactored error path when polling needed but not supported
---
drivers/firmware/arm_scmi/common.h | 11 +++++++++++
drivers/firmware/arm_scmi/driver.c | 17 +++++++++++++++++
2 files changed, 28 insertions(+)

diff --git a/drivers/firmware/arm_scmi/common.h b/drivers/firmware/arm_scmi/common.h
index 6438b5248c24..99b74f4d39b6 100644
--- a/drivers/firmware/arm_scmi/common.h
+++ b/drivers/firmware/arm_scmi/common.h
@@ -339,11 +339,19 @@ void scmi_protocol_release(const struct scmi_handle *handle, u8 protocol_id);
* @dev: Reference to device in the SCMI hierarchy corresponding to this
* channel
* @handle: Pointer to SCMI entity handle
+ * @no_completion_irq: Flag to indicate that this channel has no completion
+ * interrupt mechanism for synchronous commands.
+ * This can be dynamically set by transports at run-time
+ * inside their provided .chan_setup().
+ * @polling_enabled: Flag used to annotate if polling mode is currently enabled
+ * on this channel.
* @transport_info: Transport layer related information
*/
struct scmi_chan_info {
struct device *dev;
struct scmi_handle *handle;
+ bool no_completion_irq;
+ bool polling_enabled;
void *transport_info;
};

@@ -402,6 +410,8 @@ struct scmi_device *scmi_child_dev_find(struct device *parent,
* be pending simultaneously in the system. May be overridden by the
* get_max_msg op.
* @max_msg_size: Maximum size of data per message that can be handled.
+ * @force_polling: Flag to force this whole transport to use SCMI core polling
+ * mechanism instead of completion interrupts even if available.
*/
struct scmi_desc {
int (*transport_init)(void);
@@ -410,6 +420,7 @@ struct scmi_desc {
int max_rx_timeout_ms;
int max_msg;
int max_msg_size;
+ const bool force_polling;
};

#ifdef CONFIG_ARM_SCMI_TRANSPORT_MAILBOX
diff --git a/drivers/firmware/arm_scmi/driver.c b/drivers/firmware/arm_scmi/driver.c
index 476b91845e40..8a30b832899c 100644
--- a/drivers/firmware/arm_scmi/driver.c
+++ b/drivers/firmware/arm_scmi/driver.c
@@ -817,6 +817,7 @@ static int do_xfer(const struct scmi_protocol_handle *ph,
struct device *dev = info->dev;
struct scmi_chan_info *cinfo;

+ /* Check for polling request on custom command xfers at first */
if (xfer->hdr.poll_completion && !info->desc->ops->poll_done) {
dev_warn_once(dev,
"Polling mode is not supported by transport.\n");
@@ -827,6 +828,10 @@ static int do_xfer(const struct scmi_protocol_handle *ph,
if (unlikely(!cinfo))
return -EINVAL;

+ /* Initialized to true ONLY if also supported by transport. */
+ if (cinfo->polling_enabled)
+ xfer->hdr.poll_completion = true;
+
/*
* Initialise protocol id now from protocol handle to avoid it being
* overridden by mistake (or malice) by the protocol code mangling with
@@ -1527,6 +1532,18 @@ static int scmi_chan_setup(struct scmi_info *info, struct device *dev,
if (ret)
return ret;

+ if (tx && (cinfo->no_completion_irq || info->desc->force_polling)) {
+ if (info->desc->ops->poll_done) {
+ dev_info(dev,
+ "Enabled polling mode TX channel - prot_id:%d\n",
+ prot_id);
+ cinfo->polling_enabled = true;
+ } else {
+ dev_warn(dev,
+ "Polling mode NOT supported by transport.\n");
+ }
+ }
+
idr_alloc:
ret = idr_alloc(idr, cinfo, prot_id, prot_id + 1, GFP_KERNEL);
if (ret != prot_id) {
--
2.17.1